diff --git a/dictionaries/cs_wordlist.combined.gz b/dictionaries/cs_wordlist.combined.gz
index d69ef64..7829d65 100644
--- a/dictionaries/cs_wordlist.combined.gz
+++ b/dictionaries/cs_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/da_wordlist.combined.gz b/dictionaries/da_wordlist.combined.gz
index 919d28e..e714019 100644
--- a/dictionaries/da_wordlist.combined.gz
+++ b/dictionaries/da_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/de_wordlist.combined.gz b/dictionaries/de_wordlist.combined.gz
index f5cce9d..6a4bd44 100644
--- a/dictionaries/de_wordlist.combined.gz
+++ b/dictionaries/de_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/en_GB_wordlist.combined.gz b/dictionaries/en_GB_wordlist.combined.gz
index afef676..839f3ef 100644
--- a/dictionaries/en_GB_wordlist.combined.gz
+++ b/dictionaries/en_GB_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/en_US_wordlist.combined.gz b/dictionaries/en_US_wordlist.combined.gz
index eafbc9d..5595c75 100644
--- a/dictionaries/en_US_wordlist.combined.gz
+++ b/dictionaries/en_US_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/en_wordlist.combined.gz b/dictionaries/en_wordlist.combined.gz
index 9cbca0b..69c39d5 100644
--- a/dictionaries/en_wordlist.combined.gz
+++ b/dictionaries/en_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/es_wordlist.combined.gz b/dictionaries/es_wordlist.combined.gz
index 53b8607..0a48b6d 100644
--- a/dictionaries/es_wordlist.combined.gz
+++ b/dictionaries/es_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/fi_wordlist.combined.gz b/dictionaries/fi_wordlist.combined.gz
index 2720116..eefbfe5 100644
--- a/dictionaries/fi_wordlist.combined.gz
+++ b/dictionaries/fi_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/fr_wordlist.combined.gz b/dictionaries/fr_wordlist.combined.gz
index 1815e47..1a18320 100644
--- a/dictionaries/fr_wordlist.combined.gz
+++ b/dictionaries/fr_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/hr_wordlist.combined.gz b/dictionaries/hr_wordlist.combined.gz
index 7694a2a..864f676 100644
--- a/dictionaries/hr_wordlist.combined.gz
+++ b/dictionaries/hr_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/it_wordlist.combined.gz b/dictionaries/it_wordlist.combined.gz
index 3b84cd7..dfb1752 100644
--- a/dictionaries/it_wordlist.combined.gz
+++ b/dictionaries/it_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/lt_wordlist.combined.gz b/dictionaries/lt_wordlist.combined.gz
index 316a5af..029722d 100644
--- a/dictionaries/lt_wordlist.combined.gz
+++ b/dictionaries/lt_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/lv_wordlist.combined.gz b/dictionaries/lv_wordlist.combined.gz
index b036ac2..41e1c28 100644
--- a/dictionaries/lv_wordlist.combined.gz
+++ b/dictionaries/lv_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/nb_wordlist.combined.gz b/dictionaries/nb_wordlist.combined.gz
index b6e0d42..b699912 100644
--- a/dictionaries/nb_wordlist.combined.gz
+++ b/dictionaries/nb_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/nl_wordlist.combined.gz b/dictionaries/nl_wordlist.combined.gz
index 48ab0f4..89c2388 100644
--- a/dictionaries/nl_wordlist.combined.gz
+++ b/dictionaries/nl_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/pl_wordlist.combined.gz b/dictionaries/pl_wordlist.combined.gz
index bf02298..2b53f69 100644
--- a/dictionaries/pl_wordlist.combined.gz
+++ b/dictionaries/pl_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/pt_BR_wordlist.combined.gz b/dictionaries/pt_BR_wordlist.combined.gz
index 876eb71..2d22447 100644
--- a/dictionaries/pt_BR_wordlist.combined.gz
+++ b/dictionaries/pt_BR_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/pt_PT_wordlist.combined.gz b/dictionaries/pt_PT_wordlist.combined.gz
index 4068690..1504165 100644
--- a/dictionaries/pt_PT_wordlist.combined.gz
+++ b/dictionaries/pt_PT_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/sl_wordlist.combined.gz b/dictionaries/sl_wordlist.combined.gz
index 41a576b..55e1bb1 100644
--- a/dictionaries/sl_wordlist.combined.gz
+++ b/dictionaries/sl_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/sr_wordlist.combined.gz b/dictionaries/sr_wordlist.combined.gz
index dec6ae8..8488a08 100644
--- a/dictionaries/sr_wordlist.combined.gz
+++ b/dictionaries/sr_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/sv_wordlist.combined.gz b/dictionaries/sv_wordlist.combined.gz
index 0471772..6342520 100644
--- a/dictionaries/sv_wordlist.combined.gz
+++ b/dictionaries/sv_wordlist.combined.gz
Binary files differ
diff --git a/dictionaries/tr_wordlist.combined.gz b/dictionaries/tr_wordlist.combined.gz
index fae79ca..0251778 100644
--- a/dictionaries/tr_wordlist.combined.gz
+++ b/dictionaries/tr_wordlist.combined.gz
Binary files differ
diff --git a/java/res/raw/main_de.dict b/java/res/raw/main_de.dict
index 5d35e64..69796bb 100644
--- a/java/res/raw/main_de.dict
+++ b/java/res/raw/main_de.dict
Binary files differ
diff --git a/java/res/raw/main_en.dict b/java/res/raw/main_en.dict
index 8660c28..bef6b10 100644
--- a/java/res/raw/main_en.dict
+++ b/java/res/raw/main_en.dict
Binary files differ
diff --git a/java/res/raw/main_es.dict b/java/res/raw/main_es.dict
index f5906c2..261ab8c 100644
--- a/java/res/raw/main_es.dict
+++ b/java/res/raw/main_es.dict
Binary files differ
diff --git a/java/res/raw/main_fr.dict b/java/res/raw/main_fr.dict
index 0d2e518..18f5298 100644
--- a/java/res/raw/main_fr.dict
+++ b/java/res/raw/main_fr.dict
Binary files differ
diff --git a/java/res/raw/main_it.dict b/java/res/raw/main_it.dict
index 523f645..e161c24 100644
--- a/java/res/raw/main_it.dict
+++ b/java/res/raw/main_it.dict
Binary files differ
diff --git a/java/res/raw/main_pt_br.dict b/java/res/raw/main_pt_br.dict
index 98a27c7..21bbe7c 100644
--- a/java/res/raw/main_pt_br.dict
+++ b/java/res/raw/main_pt_br.dict
Binary files differ
diff --git a/java/res/values/strings.xml b/java/res/values/strings.xml
index 69da1e8..06f4b47 100644
--- a/java/res/values/strings.xml
+++ b/java/res/values/strings.xml
@@ -174,6 +174,11 @@
     <!-- Spoken description when there is no text entered -->
     <string name="spoken_no_text_entered">No text entered</string>
 
+    <!-- Spoken description to let the user know what auto-correction will be performed when a key is pressed. -->
+    <string name="spoken_auto_correct"><xliff:g id="key" example="Space">%1$s</xliff:g> corrects <xliff:g id="original">%2$s</xliff:g> to <xliff:g id="corrected">%3$s</xliff:g></string>
+    <!-- Spoken description used during obscured (e.g. password) entry to let the user know that auto-correction will be performed when a key is pressed. -->
+    <string name="spoken_auto_correct_obscured"><xliff:g id="key" example="Space">%1$s</xliff:g> has auto-correction</string>
+
     <!-- Spoken description for unknown keyboard keys. -->
     <string name="spoken_description_unknown">Key code %d</string>
     <!-- Spoken description for the "Shift" keyboard key when "Shift" is off. -->
diff --git a/java/src/com/android/inputmethod/accessibility/AccessibilityEntityProvider.java b/java/src/com/android/inputmethod/accessibility/AccessibilityEntityProvider.java
index 7639432..c628c5b 100644
--- a/java/src/com/android/inputmethod/accessibility/AccessibilityEntityProvider.java
+++ b/java/src/com/android/inputmethod/accessibility/AccessibilityEntityProvider.java
@@ -35,6 +35,8 @@
 import com.android.inputmethod.keyboard.Key;
 import com.android.inputmethod.keyboard.Keyboard;
 import com.android.inputmethod.keyboard.KeyboardView;
+import com.android.inputmethod.latin.settings.Settings;
+import com.android.inputmethod.latin.settings.SettingsValues;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 import com.android.inputmethod.latin.utils.CoordinateUtils;
 
@@ -285,9 +287,15 @@
     private String getKeyDescription(final Key key) {
         final EditorInfo editorInfo = mInputMethodService.getCurrentInputEditorInfo();
         final boolean shouldObscure = mAccessibilityUtils.shouldObscureInput(editorInfo);
-        final String keyDescription = mKeyCodeDescriptionMapper.getDescriptionForKey(
+        final SettingsValues currentSettings = Settings.getInstance().getCurrent();
+        final String keyCodeDescription = mKeyCodeDescriptionMapper.getDescriptionForKey(
                 mKeyboardView.getContext(), mKeyboardView.getKeyboard(), key, shouldObscure);
-        return keyDescription;
+        if (currentSettings.isWordSeparator(key.getCode())) {
+            return mAccessibilityUtils.getAutoCorrectionDescription(
+                    keyCodeDescription, shouldObscure);
+        } else {
+            return keyCodeDescription;
+        }
     }
 
     /**
diff --git a/java/src/com/android/inputmethod/accessibility/AccessibilityUtils.java b/java/src/com/android/inputmethod/accessibility/AccessibilityUtils.java
index 8929dc7..10fb9fe 100644
--- a/java/src/com/android/inputmethod/accessibility/AccessibilityUtils.java
+++ b/java/src/com/android/inputmethod/accessibility/AccessibilityUtils.java
@@ -23,6 +23,7 @@
 import android.os.SystemClock;
 import android.provider.Settings;
 import android.support.v4.view.accessibility.AccessibilityEventCompat;
+import android.text.TextUtils;
 import android.util.Log;
 import android.view.MotionEvent;
 import android.view.View;
@@ -34,6 +35,7 @@
 
 import com.android.inputmethod.compat.SettingsSecureCompatUtils;
 import com.android.inputmethod.latin.R;
+import com.android.inputmethod.latin.SuggestedWords;
 import com.android.inputmethod.latin.utils.InputTypeUtils;
 
 public final class AccessibilityUtils {
@@ -48,6 +50,12 @@
     private AccessibilityManager mAccessibilityManager;
     private AudioManager mAudioManager;
 
+    /** The most recent auto-correction. */
+    private String mAutoCorrectionWord;
+
+    /** The most recent typed word for auto-correction. */
+    private String mTypedWord;
+
     /*
      * Setting this constant to {@code false} will disable all keyboard
      * accessibility code, regardless of whether Accessibility is turned on in
@@ -142,6 +150,51 @@
     }
 
     /**
+     * Sets the current auto-correction word and typed word. These may be used
+     * to provide the user with a spoken description of what auto-correction
+     * will occur when a key is typed.
+     *
+     * @param suggestedWords the list of suggested auto-correction words
+     * @param typedWord the currently typed word
+     */
+    public void setAutoCorrection(final SuggestedWords suggestedWords, final String typedWord) {
+        if (suggestedWords != null && suggestedWords.mWillAutoCorrect) {
+            mAutoCorrectionWord = suggestedWords.getWord(SuggestedWords.INDEX_OF_AUTO_CORRECTION);
+            mTypedWord = typedWord;
+        } else {
+            mAutoCorrectionWord = null;
+            mTypedWord = null;
+        }
+    }
+
+    /**
+     * Obtains a description for an auto-correction key, taking into account the
+     * currently typed word and auto-correction.
+     *
+     * @param keyCodeDescription spoken description of the key that will insert
+     *            an auto-correction
+     * @param shouldObscure whether the key should be obscured
+     * @return a description including a description of the auto-correction, if
+     *         needed
+     */
+    public String getAutoCorrectionDescription(
+            final String keyCodeDescription, final boolean shouldObscure) {
+        if (!TextUtils.isEmpty(mAutoCorrectionWord)) {
+            if (!TextUtils.equals(mAutoCorrectionWord, mTypedWord)) {
+                if (shouldObscure) {
+                    // This should never happen, but just in case...
+                    return mContext.getString(R.string.spoken_auto_correct_obscured,
+                            keyCodeDescription);
+                }
+                return mContext.getString(R.string.spoken_auto_correct, keyCodeDescription,
+                        mTypedWord, mAutoCorrectionWord);
+            }
+        }
+
+        return keyCodeDescription;
+    }
+
+    /**
      * Sends the specified text to the {@link AccessibilityManager} to be
      * spoken.
      *
diff --git a/java/src/com/android/inputmethod/keyboard/EmojiKeyboardView.java b/java/src/com/android/inputmethod/keyboard/EmojiKeyboardView.java
index 61dc56e..eb48d01 100644
--- a/java/src/com/android/inputmethod/keyboard/EmojiKeyboardView.java
+++ b/java/src/com/android/inputmethod/keyboard/EmojiKeyboardView.java
@@ -718,12 +718,14 @@
 
             @Override
             public void run() {
+                int repeatCount = 1;
                 int timeCount = 0;
                 while (timeCount < MAX_REPEAT_COUNT_TIME && !mAborted) {
                     if (timeCount > mKeyRepeatStartTimeout) {
-                        pressDelete();
+                        pressDelete(repeatCount);
                     }
                     timeCount += mKeyRepeatInterval;
+                    ++repeatCount;
                     try {
                         Thread.sleep(mKeyRepeatInterval);
                     } catch (InterruptedException e) {
@@ -736,9 +738,9 @@
             }
         }
 
-        public void pressDelete() {
+        public void pressDelete(int repeatCount) {
             mKeyboardActionListener.onPressKey(
-                    Constants.CODE_DELETE, 0 /* repeatCount */, true /* isSinglePointer */);
+                    Constants.CODE_DELETE, repeatCount, true /* isSinglePointer */);
             mKeyboardActionListener.onCodeInput(
                     Constants.CODE_DELETE, NOT_A_COORDINATE, NOT_A_COORDINATE);
             mKeyboardActionListener.onReleaseKey(
@@ -754,7 +756,7 @@
             switch(event.getAction()) {
                 case MotionEvent.ACTION_DOWN:
                     v.setBackgroundColor(mDeleteKeyPressedBackgroundColor);
-                    pressDelete();
+                    pressDelete(0 /* repeatCount */);
                     startRepeat();
                     return true;
                 case MotionEvent.ACTION_UP:
diff --git a/java/src/com/android/inputmethod/latin/AbstractDictionaryWriter.java b/java/src/com/android/inputmethod/latin/AbstractDictionaryWriter.java
index 845a9b9..4a0ce37 100644
--- a/java/src/com/android/inputmethod/latin/AbstractDictionaryWriter.java
+++ b/java/src/com/android/inputmethod/latin/AbstractDictionaryWriter.java
@@ -25,6 +25,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.util.Map;
 
 // TODO: Quit extending Dictionary after implementing dynamic binary dictionary.
 abstract public class AbstractDictionaryWriter extends Dictionary {
@@ -50,16 +51,16 @@
 
     abstract public void removeBigramWords(final String word0, final String word1);
 
-    abstract protected void writeDictionary(final DictEncoder dictEncoder)
-            throws IOException, UnsupportedFormatException;
+    abstract protected void writeDictionary(final DictEncoder dictEncoder,
+            final Map<String, String> attributeMap) throws IOException, UnsupportedFormatException;
 
-    public void write(final String fileName) {
+    public void write(final String fileName, final Map<String, String> attributeMap) {
         final String tempFileName = fileName + ".temp";
         final File file = new File(mContext.getFilesDir(), fileName);
         final File tempFile = new File(mContext.getFilesDir(), tempFileName);
         try {
             final DictEncoder dictEncoder = new Ver3DictEncoder(tempFile);
-            writeDictionary(dictEncoder);
+            writeDictionary(dictEncoder, attributeMap);
             tempFile.renameTo(file);
         } catch (IOException e) {
             Log.e(TAG, "IO exception while writing file", e);
diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionary.java b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
index 6ec7aee..29c6c04 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
@@ -115,7 +115,7 @@
     private static native long openNative(String sourceDir, long dictOffset, long dictSize,
             boolean isUpdatable);
     private static native void flushNative(long dict, String filePath);
-    private static native boolean needsToRunGCNative(long dict);
+    private static native boolean needsToRunGCNative(long dict, boolean mindsBlockByGC);
     private static native void flushWithGCNative(long dict, String filePath);
     private static native void closeNative(long dict);
     private static native int getProbabilityNative(long dict, int[] word);
@@ -270,7 +270,7 @@
     }
 
     private void runGCIfRequired() {
-        if (needsToRunGCNative(mNativeDict)) {
+        if (needsToRunGC(true /* mindsBlockByGC */)) {
             flushWithGC();
         }
     }
@@ -326,9 +326,15 @@
         reopen();
     }
 
-    public boolean needsToRunGC() {
+    /**
+     * Checks whether GC is needed to run or not.
+     * @param mindsBlockByGC Whether to mind operations blocked by GC. We don't need to care about
+     * the blocking in some situations such as in idle time or just before closing.
+     * @return whether GC is needed to run or not.
+     */
+    public boolean needsToRunGC(final boolean mindsBlockByGC) {
         if (!isValidDictionary()) return false;
-        return needsToRunGCNative(mNativeDict);
+        return needsToRunGCNative(mNativeDict, mindsBlockByGC);
     }
 
     @UsedForTesting
diff --git a/java/src/com/android/inputmethod/latin/DictionaryFactory.java b/java/src/com/android/inputmethod/latin/DictionaryFactory.java
index 3721132..828e54f 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryFactory.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryFactory.java
@@ -51,7 +51,7 @@
         if (null == locale) {
             Log.e(TAG, "No locale defined for dictionary");
             return new DictionaryCollection(Dictionary.TYPE_MAIN,
-                    createBinaryDictionary(context, locale));
+                    createReadOnlyBinaryDictionary(context, locale));
         }
 
         final LinkedList<Dictionary> dictList = CollectionUtils.newLinkedList();
@@ -59,11 +59,11 @@
                 BinaryDictionaryGetter.getDictionaryFiles(locale, context);
         if (null != assetFileList) {
             for (final AssetFileAddress f : assetFileList) {
-                final BinaryDictionary binaryDictionary = new BinaryDictionary(f.mFilename,
-                        f.mOffset, f.mLength, useFullEditDistance, locale, Dictionary.TYPE_MAIN,
-                        false /* isUpdatable */);
-                if (binaryDictionary.isValidDictionary()) {
-                    dictList.add(binaryDictionary);
+                final ReadOnlyBinaryDictionary readOnlyBinaryDictionary =
+                        new ReadOnlyBinaryDictionary(f.mFilename, f.mOffset, f.mLength,
+                                useFullEditDistance, locale, Dictionary.TYPE_MAIN);
+                if (readOnlyBinaryDictionary.isValidDictionary()) {
+                    dictList.add(readOnlyBinaryDictionary);
                 }
             }
         }
@@ -89,12 +89,12 @@
     }
 
     /**
-     * Initializes a dictionary from a raw resource file
+     * Initializes a read-only binary dictionary from a raw resource file
      * @param context application context for reading resources
      * @param locale the locale to use for the resource
-     * @return an initialized instance of BinaryDictionary
+     * @return an initialized instance of ReadOnlyBinaryDictionary
      */
-    protected static BinaryDictionary createBinaryDictionary(final Context context,
+    protected static ReadOnlyBinaryDictionary createReadOnlyBinaryDictionary(final Context context,
             final Locale locale) {
         AssetFileDescriptor afd = null;
         try {
@@ -113,9 +113,8 @@
                 Log.e(TAG, "sourceDir is not a file: " + sourceDir);
                 return null;
             }
-            return new BinaryDictionary(sourceDir, afd.getStartOffset(), afd.getLength(),
-                    false /* useFullEditDistance */, locale, Dictionary.TYPE_MAIN,
-                    false /* isUpdatable */);
+            return new ReadOnlyBinaryDictionary(sourceDir, afd.getStartOffset(), afd.getLength(),
+                    false /* useFullEditDistance */, locale, Dictionary.TYPE_MAIN);
         } catch (android.content.res.Resources.NotFoundException e) {
             Log.e(TAG, "Could not find the resource");
             return null;
@@ -142,10 +141,10 @@
         final DictionaryCollection dictionaryCollection =
                 new DictionaryCollection(Dictionary.TYPE_MAIN);
         for (final AssetFileAddress address : dictionaryList) {
-            final BinaryDictionary binaryDictionary = new BinaryDictionary(address.mFilename,
-                    address.mOffset, address.mLength, useFullEditDistance, locale,
-                    Dictionary.TYPE_MAIN, false /* isUpdatable */);
-            dictionaryCollection.addDictionary(binaryDictionary);
+            final ReadOnlyBinaryDictionary readOnlyBinaryDictionary = new ReadOnlyBinaryDictionary(
+                    address.mFilename, address.mOffset, address.mLength, useFullEditDistance,
+                    locale, Dictionary.TYPE_MAIN);
+            dictionaryCollection.addDictionary(readOnlyBinaryDictionary);
         }
         return dictionaryCollection;
     }
diff --git a/java/src/com/android/inputmethod/latin/DictionaryWriter.java b/java/src/com/android/inputmethod/latin/DictionaryWriter.java
index 5a453dd..84abfa6 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryWriter.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryWriter.java
@@ -31,6 +31,7 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.Map;
 
 /**
  * An in memory dictionary for memorizing entries and writing a binary dictionary.
@@ -84,8 +85,11 @@
     }
 
     @Override
-    protected void writeDictionary(final DictEncoder dictEncoder)
-            throws IOException, UnsupportedFormatException {
+    protected void writeDictionary(final DictEncoder dictEncoder,
+            final Map<String, String> attributeMap) throws IOException, UnsupportedFormatException {
+        for (final Map.Entry<String, String> entry : attributeMap.entrySet()) {
+            mFusionDictionary.addOptionAttribute(entry.getKey(), entry.getValue());
+        }
         dictEncoder.writeDictionary(mFusionDictionary, FORMAT_OPTIONS);
     }
 
diff --git a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
index d3da068..2d1ca51 100644
--- a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
@@ -236,6 +236,7 @@
         HashMap<String, String> attributeMap = new HashMap<String, String>();
         attributeMap.put(FormatSpec.FileHeader.SUPPORTS_DYNAMIC_UPDATE_ATTRIBUTE,
                 SUPPORTS_DYNAMIC_UPDATE);
+        attributeMap.put(FormatSpec.FileHeader.DICTIONARY_ID_ATTRIBUTE, mFilename);
         return attributeMap;
     }
 
@@ -496,7 +497,7 @@
         if (needsToReloadBeforeWriting()) {
             mDictionaryWriter.clear();
             loadDictionaryAsync();
-            mDictionaryWriter.write(mFilename);
+            mDictionaryWriter.write(mFilename, getHeaderAttributeMap());
         } else {
             if (ENABLE_BINARY_DICTIONARY_DYNAMIC_UPDATE) {
                 if (mBinaryDictionary == null || !mBinaryDictionary.isValidDictionary()) {
@@ -504,14 +505,14 @@
                     BinaryDictionary.createEmptyDictFile(file.getAbsolutePath(),
                             DICTIONARY_FORMAT_VERSION, getHeaderAttributeMap());
                 } else {
-                    if (mBinaryDictionary.needsToRunGC()) {
+                    if (mBinaryDictionary.needsToRunGC(false /* mindsBlockByGC */)) {
                         mBinaryDictionary.flushWithGC();
                     } else {
                         mBinaryDictionary.flush();
                     }
                 }
             } else {
-                mDictionaryWriter.write(mFilename);
+                mDictionaryWriter.write(mFilename, getHeaderAttributeMap());
             }
         }
     }
diff --git a/java/src/com/android/inputmethod/latin/LatinIME.java b/java/src/com/android/inputmethod/latin/LatinIME.java
index 5fbbc17..96e16de 100644
--- a/java/src/com/android/inputmethod/latin/LatinIME.java
+++ b/java/src/com/android/inputmethod/latin/LatinIME.java
@@ -81,7 +81,7 @@
 import com.android.inputmethod.latin.personalization.PersonalizationDictionarySessionRegister;
 import com.android.inputmethod.latin.personalization.PersonalizationHelper;
 import com.android.inputmethod.latin.personalization.PersonalizationPredictionDictionary;
-import com.android.inputmethod.latin.personalization.UserHistoryPredictionDictionary;
+import com.android.inputmethod.latin.personalization.UserHistoryDictionary;
 import com.android.inputmethod.latin.settings.Settings;
 import com.android.inputmethod.latin.settings.SettingsActivity;
 import com.android.inputmethod.latin.settings.SettingsValues;
@@ -179,7 +179,7 @@
 
     private boolean mIsMainDictionaryAvailable;
     private UserBinaryDictionary mUserDictionary;
-    private UserHistoryPredictionDictionary mUserHistoryPredictionDictionary;
+    private UserHistoryDictionary mUserHistoryDictionary;
     private PersonalizationPredictionDictionary mPersonalizationPredictionDictionary;
     private PersonalizationDictionary mPersonalizationDictionary;
     private boolean mIsUserDictionaryAvailable;
@@ -623,9 +623,9 @@
 
         final SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
 
-        mUserHistoryPredictionDictionary = PersonalizationHelper
-                .getUserHistoryPredictionDictionary(this, localeStr, prefs);
-        newSuggest.setUserHistoryPredictionDictionary(mUserHistoryPredictionDictionary);
+        mUserHistoryDictionary = PersonalizationHelper.getUserHistoryDictionary(
+                this, localeStr, prefs);
+        newSuggest.setUserHistoryDictionary(mUserHistoryDictionary);
         mPersonalizationDictionary = PersonalizationHelper
                 .getPersonalizationDictionary(this, localeStr, prefs);
         newSuggest.setPersonalizationDictionary(mPersonalizationDictionary);
@@ -2557,6 +2557,8 @@
     private void showSuggestionStripWithTypedWord(final SuggestedWords suggestedWords,
             final String typedWord) {
       if (suggestedWords.isEmpty()) {
+          // No auto-correction is available, clear the cached values.
+          AccessibilityUtils.getInstance().setAutoCorrection(null, null);
           clearSuggestionStrip();
           return;
       }
@@ -2565,6 +2567,9 @@
       setSuggestedWords(suggestedWords, isAutoCorrection);
       setAutoCorrectionIndicator(isAutoCorrection);
       setSuggestionStripShown(isSuggestionsStripVisible());
+      // An auto-correction is available, cache it in accessibility code so
+      // we can be speak it if the user touches a key that will insert it.
+      AccessibilityUtils.getInstance().setAutoCorrection(suggestedWords, typedWord);
     }
 
     private void showSuggestionStrip(final SuggestedWords suggestedWords) {
@@ -2750,9 +2755,8 @@
         final SettingsValues currentSettings = mSettings.getCurrent();
         if (!currentSettings.mCorrectionEnabled) return null;
 
-        final UserHistoryPredictionDictionary userHistoryPredictionDictionary =
-                mUserHistoryPredictionDictionary;
-        if (userHistoryPredictionDictionary == null) return null;
+        final UserHistoryDictionary userHistoryDictionary = mUserHistoryDictionary;
+        if (userHistoryDictionary == null) return null;
 
         final String prevWord = mConnection.getNthPreviousWord(currentSettings.mWordSeparators, 2);
         final String secondWord;
@@ -2766,8 +2770,7 @@
         final int maxFreq = AutoCorrectionUtils.getMaxFrequency(
                 suggest.getUnigramDictionaries(), suggestion);
         if (maxFreq == 0) return null;
-        userHistoryPredictionDictionary
-                .addToPersonalizationPredictionDictionary(prevWord, secondWord, maxFreq > 0);
+        userHistoryDictionary.addToDictionary(prevWord, secondWord, maxFreq > 0);
         return prevWord;
     }
 
@@ -2953,7 +2956,7 @@
         }
         mConnection.deleteSurroundingText(deleteLength, 0);
         if (!TextUtils.isEmpty(previousWord) && !TextUtils.isEmpty(committedWord)) {
-            mUserHistoryPredictionDictionary.cancelAddingUserHistory(previousWord, committedWord);
+            mUserHistoryDictionary.cancelAddingUserHistory(previousWord, committedWord);
         }
         final String stringToCommit = originallyTypedWord + mLastComposedWord.mSeparatorString;
         if (mSettings.getCurrent().mCurrentLanguageHasSpaces) {
diff --git a/java/src/com/android/inputmethod/latin/ReadOnlyBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ReadOnlyBinaryDictionary.java
new file mode 100644
index 0000000..68505ce
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/ReadOnlyBinaryDictionary.java
@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.inputmethod.latin;
+
+import com.android.inputmethod.keyboard.ProximityInfo;
+import com.android.inputmethod.latin.SuggestedWords.SuggestedWordInfo;
+
+import java.util.ArrayList;
+import java.util.Locale;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+/**
+ * This class provides binary dictionary reading operations with locking. An instance of this class
+ * can be used by multiple threads. Note that different session IDs must be used when multiple
+ * threads get suggestions using this class.
+ */
+public final class ReadOnlyBinaryDictionary extends Dictionary {
+    /**
+     * A lock for accessing binary dictionary. Only closing binary dictionary is the operation
+     * that change the state of dictionary.
+     */
+    private final ReentrantReadWriteLock mLock = new ReentrantReadWriteLock();
+
+    private final BinaryDictionary mBinaryDictionary;
+
+    public ReadOnlyBinaryDictionary(final String filename, final long offset, final long length,
+            final boolean useFullEditDistance, final Locale locale, final String dictType) {
+        super(dictType);
+        mBinaryDictionary = new BinaryDictionary(filename, offset, length, useFullEditDistance,
+                locale, dictType, false /* isUpdatable */);
+    }
+
+    public boolean isValidDictionary() {
+        return mBinaryDictionary.isValidDictionary();
+    }
+
+    @Override
+    public ArrayList<SuggestedWordInfo> getSuggestions(final WordComposer composer,
+            final String prevWord, final ProximityInfo proximityInfo,
+            final boolean blockOffensiveWords, final int[] additionalFeaturesOptions) {
+        return getSuggestionsWithSessionId(composer, prevWord, proximityInfo, blockOffensiveWords,
+                additionalFeaturesOptions, 0 /* sessionId */);
+    }
+
+    @Override
+    public ArrayList<SuggestedWordInfo> getSuggestionsWithSessionId(final WordComposer composer,
+            final String prevWord, final ProximityInfo proximityInfo,
+            final boolean blockOffensiveWords, final int[] additionalFeaturesOptions,
+            final int sessionId) {
+        if (mLock.readLock().tryLock()) {
+            try {
+                return mBinaryDictionary.getSuggestions(composer, prevWord, proximityInfo,
+                        blockOffensiveWords, additionalFeaturesOptions);
+            } finally {
+                mLock.readLock().unlock();
+            }
+        }
+        return null;
+    }
+
+    @Override
+    public boolean isValidWord(final String word) {
+        if (mLock.readLock().tryLock()) {
+            try {
+                return mBinaryDictionary.isValidWord(word);
+            } finally {
+                mLock.readLock().unlock();
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public boolean shouldAutoCommit(final SuggestedWordInfo candidate) {
+        if (mLock.readLock().tryLock()) {
+            try {
+                return mBinaryDictionary.shouldAutoCommit(candidate);
+            } finally {
+                mLock.readLock().unlock();
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public int getFrequency(final String word) {
+        if (mLock.readLock().tryLock()) {
+            try {
+                return mBinaryDictionary.getFrequency(word);
+            } finally {
+                mLock.readLock().unlock();
+            }
+        }
+        return NOT_A_PROBABILITY;
+    }
+
+    @Override
+    public void close() {
+        mLock.writeLock().lock();
+        try {
+            mBinaryDictionary.close();
+        } finally {
+            mLock.writeLock().unlock();
+        }
+    }
+}
diff --git a/java/src/com/android/inputmethod/latin/Suggest.java b/java/src/com/android/inputmethod/latin/Suggest.java
index 6c18c94..9fd1f53 100644
--- a/java/src/com/android/inputmethod/latin/Suggest.java
+++ b/java/src/com/android/inputmethod/latin/Suggest.java
@@ -26,7 +26,7 @@
 import com.android.inputmethod.latin.SuggestedWords.SuggestedWordInfo;
 import com.android.inputmethod.latin.personalization.PersonalizationDictionary;
 import com.android.inputmethod.latin.personalization.PersonalizationPredictionDictionary;
-import com.android.inputmethod.latin.personalization.UserHistoryPredictionDictionary;
+import com.android.inputmethod.latin.personalization.UserHistoryDictionary;
 import com.android.inputmethod.latin.settings.Settings;
 import com.android.inputmethod.latin.utils.AutoCorrectionUtils;
 import com.android.inputmethod.latin.utils.BoundedTreeSet;
@@ -190,10 +190,8 @@
         addOrReplaceDictionaryInternal(Dictionary.TYPE_CONTACTS, contactsDictionary);
     }
 
-    public void setUserHistoryPredictionDictionary(
-            final UserHistoryPredictionDictionary userHistoryPredictionDictionary) {
-        addOrReplaceDictionaryInternal(Dictionary.TYPE_USER_HISTORY,
-                userHistoryPredictionDictionary);
+    public void setUserHistoryDictionary(final UserHistoryDictionary userHistoryDictionary) {
+        addOrReplaceDictionaryInternal(Dictionary.TYPE_USER_HISTORY, userHistoryDictionary);
     }
 
     public void setPersonalizationPredictionDictionary(
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
index 6cc0bfb..af61f29 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
@@ -385,12 +385,14 @@
                         nodeSize + size, ptNode.mChildren));
             }
             nodeSize += getShortcutListSize(ptNode.mShortcutTargets);
-            if (null != ptNode.mBigrams) {
-                for (WeightedString bigram : ptNode.mBigrams) {
-                    final int offset = getOffsetToTargetPtNodeDuringUpdate(ptNodeArray,
-                            nodeSize + size + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE,
-                            FusionDictionary.findWordInTree(dict.mRootNodeArray, bigram.mWord));
-                    nodeSize += getByteSize(offset) + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE;
+            if (formatOptions.mVersion < FormatSpec.FIRST_VERSION_WITH_TERMINAL_ID) {
+                if (null != ptNode.mBigrams) {
+                    for (WeightedString bigram : ptNode.mBigrams) {
+                        final int offset = getOffsetToTargetPtNodeDuringUpdate(ptNodeArray,
+                                nodeSize + size + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE,
+                                FusionDictionary.findWordInTree(dict.mRootNodeArray, bigram.mWord));
+                        nodeSize += getByteSize(offset) + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE;
+                    }
                 }
             }
             ptNode.mCachedSize = nodeSize;
diff --git a/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java b/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
index bf3d191..411e265 100644
--- a/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
@@ -77,7 +77,7 @@
      * @param newParentAddress the absolute address of the parent.
      * @param formatOptions file format options.
      */
-    public static void updateParentAddress(final DictBuffer dictBuffer,
+    private static void updateParentAddress(final DictBuffer dictBuffer,
             final int ptNodeOriginAddress, final int newParentAddress,
             final FormatOptions formatOptions) {
         final int originalPosition = dictBuffer.position();
@@ -109,7 +109,7 @@
      * @param newParentAddress the address to be written.
      * @param formatOptions file format options.
      */
-    public static void updateParentAddresses(final DictBuffer dictBuffer,
+    private static void updateParentAddresses(final DictBuffer dictBuffer,
             final int ptNodeOriginAddress, final int newParentAddress,
             final FormatOptions formatOptions) {
         final int originalPosition = dictBuffer.position();
@@ -136,7 +136,7 @@
      * @param newChildrenAddress the absolute address of the child.
      * @param formatOptions file format options.
      */
-    public static void updateChildrenAddress(final DictBuffer dictBuffer,
+    private static void updateChildrenAddress(final DictBuffer dictBuffer,
             final int ptNodeOriginAddress, final int newChildrenAddress,
             final FormatOptions formatOptions) {
         final int originalPosition = dictBuffer.position();
diff --git a/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java b/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
index 849bff0..9481a8c 100644
--- a/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
+++ b/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
@@ -265,8 +265,12 @@
     static final String FREQ_FILE_EXTENSION = ".freq";
     // tat = Terminal Address Table
     static final String TERMINAL_ADDRESS_TABLE_FILE_EXTENSION = ".tat";
+    static final String BIGRAM_FILE_EXTENSION = ".bigram";
+    static final String BIGRAM_LOOKUP_TABLE_FILE_EXTENSION = ".bigram_lookup";
+    static final String BIGRAM_ADDRESS_TABLE_FILE_EXTENSION = ".bigram_index";
     static final int FREQUENCY_AND_FLAGS_SIZE = 2;
     static final int TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE = 3;
+    static final int BIGRAM_ADDRESS_TABLE_BLOCK_SIZE = 4;
 
     static final int NO_CHILDREN_ADDRESS = Integer.MIN_VALUE;
     static final int NO_PARENT_ADDRESS = 0;
@@ -331,9 +335,9 @@
         public static final String USES_FORGETTING_CURVE_ATTRIBUTE = "USES_FORGETTING_CURVE";
         public static final String ATTRIBUTE_VALUE_TRUE = "1";
 
-        private static final String DICTIONARY_VERSION_ATTRIBUTE = "version";
-        private static final String DICTIONARY_LOCALE_ATTRIBUTE = "locale";
-        private static final String DICTIONARY_ID_ATTRIBUTE = "dictionary";
+        public static final String DICTIONARY_VERSION_ATTRIBUTE = "version";
+        public static final String DICTIONARY_LOCALE_ATTRIBUTE = "locale";
+        public static final String DICTIONARY_ID_ATTRIBUTE = "dictionary";
         private static final String DICTIONARY_DESCRIPTION_ATTRIBUTE = "description";
         public FileHeader(final int headerSize, final DictionaryOptions dictionaryOptions,
                 final FormatOptions formatOptions) {
diff --git a/java/src/com/android/inputmethod/latin/makedict/SparseTable.java b/java/src/com/android/inputmethod/latin/makedict/SparseTable.java
index 0b9cf91..96d057a 100644
--- a/java/src/com/android/inputmethod/latin/makedict/SparseTable.java
+++ b/java/src/com/android/inputmethod/latin/makedict/SparseTable.java
@@ -18,6 +18,9 @@
 
 import com.android.inputmethod.annotations.UsedForTesting;
 
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.util.ArrayList;
@@ -147,4 +150,45 @@
             BinaryDictEncoderUtils.writeUIntToStream(contentOutStream, index, 4);
         }
     }
+
+    @UsedForTesting
+    public void writeToFiles(final File lookupTableFile, final File contentFile)
+            throws IOException {
+      FileOutputStream lookupTableOutStream = null;
+      FileOutputStream contentOutStream = null;
+        try {
+            lookupTableOutStream = new FileOutputStream(lookupTableFile);
+            contentOutStream = new FileOutputStream(contentFile);
+            write(lookupTableOutStream, contentOutStream);
+        } finally {
+            if (lookupTableOutStream != null) {
+                lookupTableOutStream.close();
+            }
+            if (contentOutStream != null) {
+                contentOutStream.close();
+            }
+        }
+    }
+
+    private static byte[] readFileToByteArray(final File file) throws IOException {
+        final byte[] contents = new byte[(int) file.length()];
+        FileInputStream inStream = null;
+        try {
+            inStream = new FileInputStream(file);
+            inStream.read(contents);
+        } finally {
+            if (inStream != null) {
+                inStream.close();
+            }
+        }
+        return contents;
+    }
+
+    @UsedForTesting
+    public static SparseTable readFromFiles(final File lookupTableFile, final File contentFile,
+            final int blockSize) throws IOException {
+        final byte[] lookupTable = readFileToByteArray(lookupTableFile);
+        final byte[] content = readFileToByteArray(contentFile);
+        return new SparseTable(lookupTable, content, blockSize);
+    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
index 4c8ff8e..0aa4319 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
@@ -42,12 +42,15 @@
     private static final int FILETYPE_TRIE = 1;
     private static final int FILETYPE_FREQUENCY = 2;
     private static final int FILETYPE_TERMINAL_ADDRESS_TABLE = 3;
+    private static final int FILETYPE_BIGRAM = 4;
 
     private final File mDictDirectory;
     private final DictionaryBufferFactory mBufferFactory;
     private DictBuffer mDictBuffer;
     private DictBuffer mFrequencyBuffer;
     private DictBuffer mTerminalAddressTableBuffer;
+    private DictBuffer mBigramBuffer;
+    private SparseTable mBigramAddressTable;
 
     @UsedForTesting
     /* package */ Ver4DictDecoder(final File dictDirectory, final int factoryFlag) {
@@ -82,6 +85,9 @@
         } else if (fileType == FILETYPE_TERMINAL_ADDRESS_TABLE) {
             return new File(mDictDirectory,
                     mDictDirectory.getName() + FormatSpec.TERMINAL_ADDRESS_TABLE_FILE_EXTENSION);
+        } else if (fileType == FILETYPE_BIGRAM) {
+            return new File(mDictDirectory,
+                    mDictDirectory.getName() + FormatSpec.BIGRAM_FILE_EXTENSION);
         } else {
             throw new RuntimeException("Unsupported kind of file : " + fileType);
         }
@@ -94,6 +100,8 @@
         mFrequencyBuffer = mBufferFactory.getDictionaryBuffer(getFile(FILETYPE_FREQUENCY));
         mTerminalAddressTableBuffer = mBufferFactory.getDictionaryBuffer(
                 getFile(FILETYPE_TERMINAL_ADDRESS_TABLE));
+        mBigramBuffer = mBufferFactory.getDictionaryBuffer(getFile(FILETYPE_BIGRAM));
+        loadBigramAddressSparseTable();
     }
 
     @Override
@@ -118,6 +126,15 @@
         return header;
     }
 
+    private void loadBigramAddressSparseTable() throws IOException {
+        final File lookupIndexFile = new File(mDictDirectory,
+                mDictDirectory.getName() + FormatSpec.BIGRAM_LOOKUP_TABLE_FILE_EXTENSION);
+        final File contentFile = new File(mDictDirectory,
+                mDictDirectory.getName() + FormatSpec.BIGRAM_ADDRESS_TABLE_FILE_EXTENSION);
+        mBigramAddressTable = SparseTable.readFromFiles(lookupIndexFile, contentFile,
+                FormatSpec.BIGRAM_ADDRESS_TABLE_BLOCK_SIZE);
+    }
+
     protected static class PtNodeReader extends DictDecoder.PtNodeReader {
         protected static int readFrequency(final DictBuffer frequencyBuffer, final int terminalId) {
             frequencyBuffer.position(terminalId * FormatSpec.FREQUENCY_AND_FLAGS_SIZE + 1);
@@ -191,8 +208,21 @@
         final ArrayList<PendingAttribute> bigrams;
         if (0 != (flags & FormatSpec.FLAG_HAS_BIGRAMS)) {
             bigrams = new ArrayList<PendingAttribute>();
-            addressPointer += PtNodeReader.readBigramAddresses(mDictBuffer, bigrams,
-                    addressPointer);
+            final int posOfBigrams = mBigramAddressTable.get(terminalId);
+            mBigramBuffer.position(posOfBigrams);
+            while (bigrams.size() < FormatSpec.MAX_BIGRAMS_IN_A_PTNODE) {
+                // If bigrams.size() reaches FormatSpec.MAX_BIGRAMS_IN_A_PTNODE,
+                // remaining bigram entries are ignored.
+                final int bigramFlags = mBigramBuffer.readUnsignedByte();
+                final int targetTerminalId = mBigramBuffer.readUnsignedInt24();
+                mTerminalAddressTableBuffer.position(
+                        targetTerminalId * FormatSpec.TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE);
+                final int targetAddress = mTerminalAddressTableBuffer.readUnsignedInt24();
+                bigrams.add(new PendingAttribute(
+                        bigramFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY,
+                        targetAddress));
+                if (0 == (bigramFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_HAS_NEXT)) break;
+            }
             if (bigrams.size() >= FormatSpec.MAX_BIGRAMS_IN_A_PTNODE) {
                 MakedictLog.d("too many bigrams in a node.");
             }
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
index 4fb8967..4c25faf 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
@@ -26,6 +26,7 @@
 import com.android.inputmethod.latin.makedict.FusionDictionary.PtNodeArray;
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
 
+import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
@@ -43,9 +44,13 @@
     private byte[] mTrieBuf;
     private int mTriePos;
     private int mHeaderSize;
+    private SparseTable mBigramAddressTable;
     private OutputStream mTrieOutStream;
     private OutputStream mFreqOutStream;
     private OutputStream mTerminalAddressTableOutStream;
+    private OutputStream mBigramOutStream;
+    private File mDictDir;
+    private String mBaseFilename;
 
     @UsedForTesting
     public Ver4DictEncoder(final File dictPlacedDir) {
@@ -55,12 +60,14 @@
     private void openStreams(final FormatOptions formatOptions, final DictionaryOptions dictOptions)
             throws FileNotFoundException, IOException {
         final FileHeader header = new FileHeader(0, dictOptions, formatOptions);
-        final String filename = header.getId() + "." + header.getVersion();
-        final File mDictDir = new File(mDictPlacedDir, filename);
-        final File trieFile = new File(mDictDir, filename + FormatSpec.TRIE_FILE_EXTENSION);
-        final File freqFile = new File(mDictDir, filename + FormatSpec.FREQ_FILE_EXTENSION);
+        mBaseFilename = header.getId() + "." + header.getVersion();
+        mDictDir = new File(mDictPlacedDir, mBaseFilename);
+        final File trieFile = new File(mDictDir, mBaseFilename + FormatSpec.TRIE_FILE_EXTENSION);
+        final File freqFile = new File(mDictDir, mBaseFilename + FormatSpec.FREQ_FILE_EXTENSION);
         final File terminalAddressTableFile = new File(mDictDir,
-                filename + FormatSpec.TERMINAL_ADDRESS_TABLE_FILE_EXTENSION);
+                mBaseFilename + FormatSpec.TERMINAL_ADDRESS_TABLE_FILE_EXTENSION);
+        final File bigramFile = new File(mDictDir,
+                mBaseFilename + FormatSpec.BIGRAM_FILE_EXTENSION);
         if (!mDictDir.isDirectory()) {
             if (mDictDir.exists()) mDictDir.delete();
             mDictDir.mkdirs();
@@ -71,6 +78,7 @@
         mTrieOutStream = new FileOutputStream(trieFile);
         mFreqOutStream = new FileOutputStream(freqFile);
         mTerminalAddressTableOutStream = new FileOutputStream(terminalAddressTableFile);
+        mBigramOutStream = new FileOutputStream(bigramFile);
     }
 
     private void close() throws IOException {
@@ -84,10 +92,14 @@
             if (mTerminalAddressTableOutStream != null) {
                 mTerminalAddressTableOutStream.close();
             }
+            if (mBigramOutStream != null) {
+                mBigramOutStream.close();
+            }
         } finally {
             mTrieOutStream = null;
             mFreqOutStream = null;
             mTerminalAddressTableOutStream = null;
+            mBigramOutStream = null;
         }
     }
 
@@ -123,6 +135,10 @@
         if (MakedictLog.DBG) BinaryDictEncoderUtils.checkFlatPtNodeArrayList(flatNodes);
 
         writeTerminalData(flatNodes, terminalCount);
+        mBigramAddressTable = new SparseTable(terminalCount,
+                FormatSpec.BIGRAM_ADDRESS_TABLE_BLOCK_SIZE);
+        writeBigrams(flatNodes, dict);
+        writeBigramAddressSparseTable();
 
         final PtNodeArray lastNodeArray = flatNodes.get(flatNodes.size() - 1);
         final int bufferSize = lastNodeArray.mCachedAddressAfterUpdate + lastNodeArray.mCachedSize;
@@ -230,24 +246,41 @@
                 shortcutByteSize, FormatSpec.PTNODE_SHORTCUT_LIST_SIZE_SIZE);
     }
 
-    private void writeBigrams(ArrayList<WeightedString> bigrams, FusionDictionary dict) {
-        if (bigrams == null) return;
+    private void writeBigrams(final ArrayList<PtNodeArray> flatNodes, final FusionDictionary dict)
+            throws IOException {
+        final ByteArrayOutputStream bigramBuffer = new ByteArrayOutputStream();
 
-        final Iterator<WeightedString> bigramIterator = bigrams.iterator();
-        while (bigramIterator.hasNext()) {
-            final WeightedString bigram = bigramIterator.next();
-            final PtNode target =
-                    FusionDictionary.findWordInTree(dict.mRootNodeArray, bigram.mWord);
-            final int addressOfBigram = target.mCachedAddressAfterUpdate;
-            final int unigramFrequencyForThisWord = target.mFrequency;
-            final int offset = addressOfBigram
-                    - (mTriePos + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE);
-            int bigramFlags = BinaryDictEncoderUtils.makeBigramFlags(bigramIterator.hasNext(),
-                    offset, bigram.mFrequency, unigramFrequencyForThisWord, bigram.mWord);
-            mTrieBuf[mTriePos++] = (byte) bigramFlags;
-            mTriePos += BinaryDictEncoderUtils.writeChildrenPosition(mTrieBuf,
-                    mTriePos, Math.abs(offset));
+        for (final PtNodeArray nodeArray : flatNodes) {
+            for (final PtNode ptNode : nodeArray.mData) {
+                if (ptNode.mBigrams != null) {
+                    final int startPos = bigramBuffer.size();
+                    mBigramAddressTable.set(ptNode.mTerminalId, startPos);
+                    final Iterator<WeightedString> bigramIterator = ptNode.mBigrams.iterator();
+                    while (bigramIterator.hasNext()) {
+                        final WeightedString bigram = bigramIterator.next();
+                        final PtNode target =
+                            FusionDictionary.findWordInTree(dict.mRootNodeArray, bigram.mWord);
+                        final int unigramFrequencyForThisWord = target.mFrequency;
+                        final int bigramFlags = BinaryDictEncoderUtils.makeBigramFlags(
+                                bigramIterator.hasNext(), 0, bigram.mFrequency,
+                                unigramFrequencyForThisWord, bigram.mWord);
+                        BinaryDictEncoderUtils.writeUIntToStream(bigramBuffer, bigramFlags,
+                                FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE);
+                        BinaryDictEncoderUtils.writeUIntToStream(bigramBuffer, target.mTerminalId,
+                                FormatSpec.PTNODE_ATTRIBUTE_MAX_ADDRESS_SIZE);
+                    }
+                }
+            }
         }
+        bigramBuffer.writeTo(mBigramOutStream);
+    }
+
+    private void writeBigramAddressSparseTable() throws IOException {
+        final File lookupIndexFile =
+                new File(mDictDir, mBaseFilename + FormatSpec.BIGRAM_LOOKUP_TABLE_FILE_EXTENSION);
+        final File contentFile =
+                new File(mDictDir, mBaseFilename + FormatSpec.BIGRAM_ADDRESS_TABLE_FILE_EXTENSION);
+        mBigramAddressTable.writeToFiles(lookupIndexFile, contentFile);
     }
 
     @Override
@@ -267,7 +300,6 @@
         }
         writeChildrenPosition(ptNode, formatOptions);
         writeShortcuts(ptNode.mShortcutTargets);
-        writeBigrams(ptNode.mBigrams, dict);
     }
 
     private void writeTerminalData(final ArrayList<PtNodeArray> flatNodes,
diff --git a/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java b/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
index 66517a8..7cf4f0c 100644
--- a/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
+++ b/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
@@ -22,6 +22,7 @@
 
 import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.latin.Constants;
+import com.android.inputmethod.latin.Dictionary;
 import com.android.inputmethod.latin.ExpandableBinaryDictionary;
 import com.android.inputmethod.latin.LatinImeLogger;
 import com.android.inputmethod.latin.makedict.DictDecoder;
@@ -50,6 +51,9 @@
     /** Any pair being typed or picked */
     public static final int FREQUENCY_FOR_TYPED = 2;
 
+    public static final int FREQUENCY_FOR_WORDS_IN_DICTS = FREQUENCY_FOR_TYPED;
+    public static final int FREQUENCY_FOR_WORDS_NOT_IN_DICTS = Dictionary.NOT_A_PROBABILITY;
+
     /** Locale for which this user history dictionary is storing words */
     private final String mLocale;
 
@@ -94,6 +98,8 @@
                 FormatSpec.FileHeader.ATTRIBUTE_VALUE_TRUE);
         attributeMap.put(FormatSpec.FileHeader.USES_FORGETTING_CURVE_ATTRIBUTE,
                 FormatSpec.FileHeader.ATTRIBUTE_VALUE_TRUE);
+        attributeMap.put(FormatSpec.FileHeader.DICTIONARY_ID_ATTRIBUTE, mFileName);
+        attributeMap.put(FormatSpec.FileHeader.DICTIONARY_LOCALE_ATTRIBUTE, mLocale);
         return attributeMap;
     }
 
@@ -117,27 +123,29 @@
     }
 
     /**
-     * Pair will be added to the personalization prediction dictionary.
+     * Pair will be added to the decaying dictionary.
      *
      * The first word may be null. That means we don't know the context, in other words,
      * it's only a unigram. The first word may also be an empty string : this means start
      * context, as in beginning of a sentence for example.
      * The second word may not be null (a NullPointerException would be thrown).
      */
-    public void addToPersonalizationPredictionDictionary(
-            final String word0, final String word1, final boolean isValid) {
+    public void addToDictionary(final String word0, final String word1, final boolean isValid) {
         if (word1.length() >= Constants.DICTIONARY_MAX_WORD_LENGTH ||
                 (word0 != null && word0.length() >= Constants.DICTIONARY_MAX_WORD_LENGTH)) {
             return;
         }
-        addWordDynamically(word1, null /* the "shortcut" parameter is null */, FREQUENCY_FOR_TYPED,
+        final int frequency = ENABLE_BINARY_DICTIONARY_DYNAMIC_UPDATE ?
+                (isValid ? FREQUENCY_FOR_WORDS_IN_DICTS : FREQUENCY_FOR_WORDS_NOT_IN_DICTS) :
+                        FREQUENCY_FOR_TYPED;
+        addWordDynamically(word1, null /* the "shortcut" parameter is null */, frequency,
                 false /* isNotAWord */);
         // Do not insert a word as a bigram of itself
         if (word1.equals(word0)) {
             return;
         }
         if (null != word0) {
-            addBigramDynamically(word0, word1, FREQUENCY_FOR_TYPED, isValid);
+            addBigramDynamically(word0, word1, frequency, isValid);
         }
     }
 
diff --git a/java/src/com/android/inputmethod/latin/personalization/DynamicPersonalizationDictionaryWriter.java b/java/src/com/android/inputmethod/latin/personalization/DynamicPersonalizationDictionaryWriter.java
index 3050885..039b253 100644
--- a/java/src/com/android/inputmethod/latin/personalization/DynamicPersonalizationDictionaryWriter.java
+++ b/java/src/com/android/inputmethod/latin/personalization/DynamicPersonalizationDictionaryWriter.java
@@ -36,6 +36,7 @@
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Map;
 
 // Currently this class is used to implement dynamic prodiction dictionary.
 // TODO: Move to native code.
@@ -113,8 +114,8 @@
     }
 
     @Override
-    protected void writeDictionary(final DictEncoder dictEncoder)
-            throws IOException, UnsupportedFormatException {
+    protected void writeDictionary(final DictEncoder dictEncoder,
+            final Map<String, String> attributeMap) throws IOException, UnsupportedFormatException {
         UserHistoryDictIOUtils.writeDictionary(dictEncoder,
                 new FrequencyProvider(mBigramList, mExpandableDictionary, mMaxHistoryBigrams),
                 mBigramList, FORMAT_OPTIONS);
diff --git a/java/src/com/android/inputmethod/latin/personalization/PersonalizationDictionaryUpdateSession.java b/java/src/com/android/inputmethod/latin/personalization/PersonalizationDictionaryUpdateSession.java
index c616a29..a86f6e5 100644
--- a/java/src/com/android/inputmethod/latin/personalization/PersonalizationDictionaryUpdateSession.java
+++ b/java/src/com/android/inputmethod/latin/personalization/PersonalizationDictionaryUpdateSession.java
@@ -110,7 +110,7 @@
         if (dictionary == null) {
             return;
         }
-        dictionary.addToPersonalizationPredictionDictionary(word0, word1, isValid);
+        dictionary.addToDictionary(word0, word1, isValid);
     }
 
     // Bulk import
@@ -122,8 +122,7 @@
             return;
         }
         for (final PersonalizationLanguageModelParam lmParam : lmParams) {
-            dictionary.addToPersonalizationPredictionDictionary(
-                    lmParam.mWord0, lmParam.mWord1, lmParam.mIsValid);
+            dictionary.addToDictionary(lmParam.mWord0, lmParam.mWord1, lmParam.mIsValid);
         }
     }
 }
diff --git a/java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java b/java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java
index 5f702ee..8c9484b 100644
--- a/java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java
+++ b/java/src/com/android/inputmethod/latin/personalization/PersonalizationHelper.java
@@ -30,7 +30,7 @@
     private static final String TAG = PersonalizationHelper.class.getSimpleName();
     private static final boolean DEBUG = false;
 
-    private static final ConcurrentHashMap<String, SoftReference<UserHistoryPredictionDictionary>>
+    private static final ConcurrentHashMap<String, SoftReference<UserHistoryDictionary>>
             sLangUserHistoryDictCache = CollectionUtils.newConcurrentHashMap();
 
     private static final ConcurrentHashMap<String, SoftReference<PersonalizationDictionary>>
@@ -41,25 +41,23 @@
                     sLangPersonalizationPredictionDictCache =
                             CollectionUtils.newConcurrentHashMap();
 
-    public static UserHistoryPredictionDictionary getUserHistoryPredictionDictionary(
+    public static UserHistoryDictionary getUserHistoryDictionary(
             final Context context, final String locale, final SharedPreferences sp) {
         synchronized (sLangUserHistoryDictCache) {
             if (sLangUserHistoryDictCache.containsKey(locale)) {
-                final SoftReference<UserHistoryPredictionDictionary> ref =
+                final SoftReference<UserHistoryDictionary> ref =
                         sLangUserHistoryDictCache.get(locale);
-                final UserHistoryPredictionDictionary dict = ref == null ? null : ref.get();
+                final UserHistoryDictionary dict = ref == null ? null : ref.get();
                 if (dict != null) {
                     if (DEBUG) {
-                        Log.w(TAG, "Use cached UserHistoryPredictionDictionary for " + locale);
+                        Log.w(TAG, "Use cached UserHistoryDictionary for " + locale);
                     }
                     dict.reloadDictionaryIfRequired();
                     return dict;
                 }
             }
-            final UserHistoryPredictionDictionary dict =
-                    new UserHistoryPredictionDictionary(context, locale, sp);
-            sLangUserHistoryDictCache.put(
-                    locale, new SoftReference<UserHistoryPredictionDictionary>(dict));
+            final UserHistoryDictionary dict = new UserHistoryDictionary(context, locale, sp);
+            sLangUserHistoryDictCache.put(locale, new SoftReference<UserHistoryDictionary>(dict));
             return dict;
         }
     }
diff --git a/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java b/java/src/com/android/inputmethod/latin/personalization/UserHistoryDictionary.java
similarity index 84%
rename from java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java
rename to java/src/com/android/inputmethod/latin/personalization/UserHistoryDictionary.java
index 38e308a..a60226d 100644
--- a/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java
+++ b/java/src/com/android/inputmethod/latin/personalization/UserHistoryDictionary.java
@@ -26,10 +26,10 @@
  * Locally gathers stats about the words user types and various other signals like auto-correction
  * cancellation or manual picks. This allows the keyboard to adapt to the typist over time.
  */
-public class UserHistoryPredictionDictionary extends DecayingExpandableBinaryDictionaryBase {
+public class UserHistoryDictionary extends DecayingExpandableBinaryDictionaryBase {
     /* package for tests */ static final String NAME =
-            UserHistoryPredictionDictionary.class.getSimpleName();
-    /* package */ UserHistoryPredictionDictionary(final Context context, final String locale,
+            UserHistoryDictionary.class.getSimpleName();
+    /* package */ UserHistoryDictionary(final Context context, final String locale,
             final SharedPreferences sp) {
         super(context, locale, sp, Dictionary.TYPE_USER_HISTORY, getDictionaryFileName(locale));
     }
diff --git a/native/jni/Android.mk b/native/jni/Android.mk
index 0594ddf..36afea5 100644
--- a/native/jni/Android.mk
+++ b/native/jni/Android.mk
@@ -85,6 +85,7 @@
     $(addprefix suggest/policyimpl/dictionary/utils/, \
         buffer_with_extendable_buffer.cpp \
         byte_array_utils.cpp \
+        decaying_utils.cpp \
         dict_file_writing_utils.cpp \
         format_utils.cpp) \
     suggest/policyimpl/gesture/gesture_suggest_policy_factory.cpp \
diff --git a/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp b/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
index 85e100e..c5ef264 100644
--- a/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
+++ b/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
@@ -113,10 +113,10 @@
 }
 
 static bool latinime_BinaryDictionary_needsToRunGC(JNIEnv *env, jclass clazz,
-        jlong dict) {
+        jlong dict, jboolean mindsBlockByGC) {
     Dictionary *dictionary = reinterpret_cast<Dictionary *>(dict);
     if (!dictionary) return false;
-    return dictionary->needsToRunGC();
+    return dictionary->needsToRunGC(mindsBlockByGC == JNI_TRUE);
 }
 
 static void latinime_BinaryDictionary_flushWithGC(JNIEnv *env, jclass clazz, jlong dict,
@@ -364,7 +364,7 @@
     },
     {
         const_cast<char *>("needsToRunGCNative"),
-        const_cast<char *>("(J)Z"),
+        const_cast<char *>("(JZ)Z"),
         reinterpret_cast<void *>(latinime_BinaryDictionary_needsToRunGC)
     },
     {
diff --git a/native/jni/src/defines.h b/native/jni/src/defines.h
index 89dfa39..c2aa8ba 100644
--- a/native/jni/src/defines.h
+++ b/native/jni/src/defines.h
@@ -375,7 +375,7 @@
     CT_TERMINAL,
     CT_TERMINAL_INSERTION,
     // Create new word with space omission
-    CT_NEW_WORD_SPACE_OMITTION,
+    CT_NEW_WORD_SPACE_OMISSION,
     // Create new word with space substitution
     CT_NEW_WORD_SPACE_SUBSTITUTION,
 } CorrectionType;
diff --git a/native/jni/src/suggest/core/dicnode/dic_node.h b/native/jni/src/suggest/core/dicnode/dic_node.h
index 41ef9d2..9099e82 100644
--- a/native/jni/src/suggest/core/dicnode/dic_node.h
+++ b/native/jni/src/suggest/core/dicnode/dic_node.h
@@ -38,10 +38,10 @@
         INTS_TO_CHARS(mDicNodeState.mDicNodeStatePrevWord.mPrevWord, \
                 mDicNodeState.mDicNodeStatePrevWord.getPrevWordLength(), prevWordCharBuf, \
                 NELEMS(prevWordCharBuf)); \
-        AKLOGI("#%8s, %5f, %5f, %5f, %5f, %s, %s, %d,,", header, \
+        AKLOGI("#%8s, %5f, %5f, %5f, %5f, %s, %s, %d, %5f,", header, \
                 getSpatialDistanceForScoring(), getLanguageDistanceForScoring(), \
                 getNormalizedCompoundDistance(), getRawLength(), prevWordCharBuf, charBuf, \
-                getInputIndex(0)); \
+                getInputIndex(0), getNormalizedCompoundDistanceAfterFirstWord()); \
         } while (0)
 #else
 #define LOGI_SHOW_ADD_COST_PROP
@@ -434,6 +434,13 @@
         return mDicNodeState.mDicNodeStateScoring.getLanguageDistance();
     }
 
+    // For space-aware gestures, we store the normalized distance at the char index
+    // that ends the first word of the suggestion. We call this the distance after
+    // first word.
+    float getNormalizedCompoundDistanceAfterFirstWord() const {
+        return mDicNodeState.mDicNodeStateScoring.getNormalizedCompoundDistanceAfterFirstWord();
+    }
+
     float getLanguageDistanceRatePerWordForScoring() const {
         const float langDist = getLanguageDistanceForScoring();
         const float totalWordCount =
@@ -565,6 +572,12 @@
                 inputSize, getTotalInputIndex(), errorType);
     }
 
+    // Saves the current normalized compound distance for space-aware gestures.
+    // See getNormalizedCompoundDistanceAfterFirstWord for details.
+    AK_FORCE_INLINE void saveNormalizedCompoundDistanceAfterFirstWordIfNoneYet() {
+        mDicNodeState.mDicNodeStateScoring.saveNormalizedCompoundDistanceAfterFirstWordIfNoneYet();
+    }
+
     // Caveat: Must not be called outside Weighting
     // This restriction is guaranteed by "friend"
     AK_FORCE_INLINE void forwardInputIndex(const int pointerId, const int count,
diff --git a/native/jni/src/suggest/core/dicnode/internal/dic_node_state_scoring.h b/native/jni/src/suggest/core/dicnode/internal/dic_node_state_scoring.h
index 4c88422..3c85d0e 100644
--- a/native/jni/src/suggest/core/dicnode/internal/dic_node_state_scoring.h
+++ b/native/jni/src/suggest/core/dicnode/internal/dic_node_state_scoring.h
@@ -31,7 +31,8 @@
               mDigraphIndex(DigraphUtils::NOT_A_DIGRAPH_INDEX),
               mEditCorrectionCount(0), mProximityCorrectionCount(0),
               mNormalizedCompoundDistance(0.0f), mSpatialDistance(0.0f), mLanguageDistance(0.0f),
-              mRawLength(0.0f), mExactMatch(true) {
+              mRawLength(0.0f), mExactMatch(true),
+              mNormalizedCompoundDistanceAfterFirstWord(MAX_VALUE_FOR_WEIGHTING) {
     }
 
     virtual ~DicNodeStateScoring() {}
@@ -45,6 +46,7 @@
         mRawLength = 0.0f;
         mDoubleLetterLevel = NOT_A_DOUBLE_LETTER;
         mDigraphIndex = DigraphUtils::NOT_A_DIGRAPH_INDEX;
+        mNormalizedCompoundDistanceAfterFirstWord = MAX_VALUE_FOR_WEIGHTING;
         mExactMatch = true;
     }
 
@@ -58,6 +60,8 @@
         mDoubleLetterLevel = scoring->mDoubleLetterLevel;
         mDigraphIndex = scoring->mDigraphIndex;
         mExactMatch = scoring->mExactMatch;
+        mNormalizedCompoundDistanceAfterFirstWord =
+                scoring->mNormalizedCompoundDistanceAfterFirstWord;
     }
 
     void addCost(const float spatialCost, const float languageCost, const bool doNormalization,
@@ -86,6 +90,17 @@
         }
     }
 
+    // Saves the current normalized distance for space-aware gestures.
+    // See getNormalizedCompoundDistanceAfterFirstWord for details.
+    void saveNormalizedCompoundDistanceAfterFirstWordIfNoneYet() {
+        // We get called here after each word. We only want to store the distance after
+        // the first word, so if we already have a distance we skip saving -- hence "IfNoneYet"
+        // in the method name.
+        if (mNormalizedCompoundDistanceAfterFirstWord >= MAX_VALUE_FOR_WEIGHTING) {
+            mNormalizedCompoundDistanceAfterFirstWord = getNormalizedCompoundDistance();
+        }
+    }
+
     void addRawLength(const float rawLength) {
         mRawLength += rawLength;
     }
@@ -102,6 +117,13 @@
         return mNormalizedCompoundDistance;
     }
 
+    // For space-aware gestures, we store the normalized distance at the char index
+    // that ends the first word of the suggestion. We call this the distance after
+    // first word.
+    float getNormalizedCompoundDistanceAfterFirstWord() const {
+        return mNormalizedCompoundDistanceAfterFirstWord;
+    }
+
     float getSpatialDistance() const {
         return mSpatialDistance;
     }
@@ -178,6 +200,7 @@
     float mLanguageDistance;
     float mRawLength;
     bool mExactMatch;
+    float mNormalizedCompoundDistanceAfterFirstWord;
 
     AK_FORCE_INLINE void addDistance(float spatialDistance, float languageDistance,
             bool doNormalization, int inputSize, int totalInputIndex) {
diff --git a/native/jni/src/suggest/core/dictionary/dictionary.cpp b/native/jni/src/suggest/core/dictionary/dictionary.cpp
index 214df1b..b1d01ed 100644
--- a/native/jni/src/suggest/core/dictionary/dictionary.cpp
+++ b/native/jni/src/suggest/core/dictionary/dictionary.cpp
@@ -33,6 +33,8 @@
 
 namespace latinime {
 
+const int Dictionary::HEADER_ATTRIBUTE_BUFFER_SIZE = 32;
+
 Dictionary::Dictionary(JNIEnv *env,
         DictionaryStructureWithBufferPolicy *const dictionaryStructureWithBufferPolicy)
         : mDictionaryStructureWithBufferPolicy(dictionaryStructureWithBufferPolicy),
@@ -121,8 +123,8 @@
     mDictionaryStructureWithBufferPolicy->flushWithGC(filePath);
 }
 
-bool Dictionary::needsToRunGC() {
-    return mDictionaryStructureWithBufferPolicy->needsToRunGC();
+bool Dictionary::needsToRunGC(const bool mindsBlockByGC) {
+    return mDictionaryStructureWithBufferPolicy->needsToRunGC(mindsBlockByGC);
 }
 
 void Dictionary::getProperty(const char *const query, char *const outResult,
@@ -131,27 +133,27 @@
 }
 
 void Dictionary::logDictionaryInfo(JNIEnv *const env) const {
-    const int BUFFER_SIZE = 16;
-    int dictionaryIdCodePointBuffer[BUFFER_SIZE];
-    int versionStringCodePointBuffer[BUFFER_SIZE];
-    int dateStringCodePointBuffer[BUFFER_SIZE];
+    int dictionaryIdCodePointBuffer[HEADER_ATTRIBUTE_BUFFER_SIZE];
+    int versionStringCodePointBuffer[HEADER_ATTRIBUTE_BUFFER_SIZE];
+    int dateStringCodePointBuffer[HEADER_ATTRIBUTE_BUFFER_SIZE];
     const DictionaryHeaderStructurePolicy *const headerPolicy =
             getDictionaryStructurePolicy()->getHeaderStructurePolicy();
     headerPolicy->readHeaderValueOrQuestionMark("dictionary", dictionaryIdCodePointBuffer,
-            BUFFER_SIZE);
+            HEADER_ATTRIBUTE_BUFFER_SIZE);
     headerPolicy->readHeaderValueOrQuestionMark("version", versionStringCodePointBuffer,
-            BUFFER_SIZE);
-    headerPolicy->readHeaderValueOrQuestionMark("date", dateStringCodePointBuffer, BUFFER_SIZE);
+            HEADER_ATTRIBUTE_BUFFER_SIZE);
+    headerPolicy->readHeaderValueOrQuestionMark("date", dateStringCodePointBuffer,
+            HEADER_ATTRIBUTE_BUFFER_SIZE);
 
-    char dictionaryIdCharBuffer[BUFFER_SIZE];
-    char versionStringCharBuffer[BUFFER_SIZE];
-    char dateStringCharBuffer[BUFFER_SIZE];
-    intArrayToCharArray(dictionaryIdCodePointBuffer, BUFFER_SIZE,
-            dictionaryIdCharBuffer, BUFFER_SIZE);
-    intArrayToCharArray(versionStringCodePointBuffer, BUFFER_SIZE,
-            versionStringCharBuffer, BUFFER_SIZE);
-    intArrayToCharArray(dateStringCodePointBuffer, BUFFER_SIZE,
-            dateStringCharBuffer, BUFFER_SIZE);
+    char dictionaryIdCharBuffer[HEADER_ATTRIBUTE_BUFFER_SIZE];
+    char versionStringCharBuffer[HEADER_ATTRIBUTE_BUFFER_SIZE];
+    char dateStringCharBuffer[HEADER_ATTRIBUTE_BUFFER_SIZE];
+    intArrayToCharArray(dictionaryIdCodePointBuffer, HEADER_ATTRIBUTE_BUFFER_SIZE,
+            dictionaryIdCharBuffer, HEADER_ATTRIBUTE_BUFFER_SIZE);
+    intArrayToCharArray(versionStringCodePointBuffer, HEADER_ATTRIBUTE_BUFFER_SIZE,
+            versionStringCharBuffer, HEADER_ATTRIBUTE_BUFFER_SIZE);
+    intArrayToCharArray(dateStringCodePointBuffer, HEADER_ATTRIBUTE_BUFFER_SIZE,
+            dateStringCharBuffer, HEADER_ATTRIBUTE_BUFFER_SIZE);
 
     LogUtils::logToJava(env,
             "Dictionary info: dictionary = %s ; version = %s ; date = %s",
diff --git a/native/jni/src/suggest/core/dictionary/dictionary.h b/native/jni/src/suggest/core/dictionary/dictionary.h
index 8007517..d8a0f3e 100644
--- a/native/jni/src/suggest/core/dictionary/dictionary.h
+++ b/native/jni/src/suggest/core/dictionary/dictionary.h
@@ -81,7 +81,7 @@
 
     void flushWithGC(const char *const filePath);
 
-    bool needsToRunGC();
+    bool needsToRunGC(const bool mindsBlockByGC);
 
     void getProperty(const char *const query, char *const outResult,
             const int maxResultLength) const;
@@ -95,6 +95,8 @@
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(Dictionary);
 
+    static const int HEADER_ATTRIBUTE_BUFFER_SIZE;
+
     DictionaryStructureWithBufferPolicy *const mDictionaryStructureWithBufferPolicy;
     const BigramDictionary *const mBigramDictionary;
     const SuggestInterface *const mGestureSuggest;
diff --git a/native/jni/src/suggest/core/policy/dictionary_structure_with_buffer_policy.h b/native/jni/src/suggest/core/policy/dictionary_structure_with_buffer_policy.h
index 2434287..c7ffef0 100644
--- a/native/jni/src/suggest/core/policy/dictionary_structure_with_buffer_policy.h
+++ b/native/jni/src/suggest/core/policy/dictionary_structure_with_buffer_policy.h
@@ -78,7 +78,7 @@
 
     virtual void flushWithGC(const char *const filePath) = 0;
 
-    virtual bool needsToRunGC() const = 0;
+    virtual bool needsToRunGC(const bool mindsBlockByGC) const = 0;
 
     virtual void getProperty(const char *const query, char *const outResult,
             const int maxResultLength) const = 0;
diff --git a/native/jni/src/suggest/core/policy/weighting.cpp b/native/jni/src/suggest/core/policy/weighting.cpp
index f9b777d..0c40168 100644
--- a/native/jni/src/suggest/core/policy/weighting.cpp
+++ b/native/jni/src/suggest/core/policy/weighting.cpp
@@ -38,7 +38,7 @@
     case CT_SUBSTITUTION:
         PROF_SUBSTITUTION(node->mProfiler);
         return;
-    case CT_NEW_WORD_SPACE_OMITTION:
+    case CT_NEW_WORD_SPACE_OMISSION:
         PROF_NEW_WORD(node->mProfiler);
         return;
     case CT_MATCH:
@@ -93,6 +93,11 @@
     }
     dicNode->addCost(spatialCost, languageCost, weighting->needsToNormalizeCompoundDistance(),
             inputSize, errorType);
+    if (CT_NEW_WORD_SPACE_OMISSION == correctionType) {
+        // When we are on a terminal, we save the current distance for evaluating
+        // when to auto-commit partial suggestions.
+        dicNode->saveNormalizedCompoundDistanceAfterFirstWordIfNoneYet();
+    }
 }
 
 /* static */ float Weighting::getSpatialCost(const Weighting *const weighting,
@@ -108,7 +113,7 @@
     case CT_SUBSTITUTION:
         // only used for typing
         return weighting->getSubstitutionCost();
-    case CT_NEW_WORD_SPACE_OMITTION:
+    case CT_NEW_WORD_SPACE_OMISSION:
         return weighting->getNewWordSpatialCost(traverseSession, dicNode, inputStateG);
     case CT_MATCH:
         return weighting->getMatchedCost(traverseSession, dicNode, inputStateG);
@@ -138,7 +143,7 @@
         return 0.0f;
     case CT_SUBSTITUTION:
         return 0.0f;
-    case CT_NEW_WORD_SPACE_OMITTION:
+    case CT_NEW_WORD_SPACE_OMISSION:
         return weighting->getNewWordBigramLanguageCost(
                 traverseSession, parentDicNode, multiBigramMap);
     case CT_MATCH:
@@ -173,7 +178,7 @@
             return 0; /* 0 because CT_MATCH will be called */
         case CT_SUBSTITUTION:
             return 0; /* 0 because CT_MATCH will be called */
-        case CT_NEW_WORD_SPACE_OMITTION:
+        case CT_NEW_WORD_SPACE_OMISSION:
             return 0;
         case CT_MATCH:
             return 1;
diff --git a/native/jni/src/suggest/core/suggest.cpp b/native/jni/src/suggest/core/suggest.cpp
index b1340e1..e20bc49 100644
--- a/native/jni/src/suggest/core/suggest.cpp
+++ b/native/jni/src/suggest/core/suggest.cpp
@@ -574,7 +574,7 @@
     DicNodeUtils::initAsRootWithPreviousWord(
             traverseSession->getDictionaryStructurePolicy(), dicNode, &newDicNode);
     const CorrectionType correctionType = spaceSubstitution ?
-            CT_NEW_WORD_SPACE_SUBSTITUTION : CT_NEW_WORD_SPACE_OMITTION;
+            CT_NEW_WORD_SPACE_SUBSTITUTION : CT_NEW_WORD_SPACE_OMISSION;
     Weighting::addCostAndForwardInputIndex(WEIGHTING, correctionType, traverseSession, dicNode,
             &newDicNode, traverseSession->getMultiBigramMap());
     if (newDicNode.getCompoundDistance() < static_cast<float>(MAX_VALUE_FOR_WEIGHTING)) {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.cpp
index e02f4cb..67a085d 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.cpp
@@ -17,10 +17,10 @@
 #include "suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.h"
 
 #include "suggest/core/policy/dictionary_shortcuts_structure_policy.h"
-#include "suggest/policyimpl/dictionary/bigram/bigram_list_read_write_utils.h"
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_node_reader.h"
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h"
 #include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
+#include "suggest/policyimpl/dictionary/utils/decaying_utils.h"
 
 namespace latinime {
 
@@ -41,9 +41,14 @@
     if (usesAdditionalBuffer && originalBigramPos != NOT_A_DICT_POS) {
         originalBigramPos += mBuffer->getOriginalBufferSize();
     }
-    *outBigramPos = followBigramLinkAndGetCurrentBigramPtNodePos(originalBigramPos);
     *outProbability = BigramListReadWriteUtils::getProbabilityFromFlags(bigramFlags);
     *outHasNext = BigramListReadWriteUtils::hasNext(bigramFlags);
+    if (mIsDecayingDict && !DecayingUtils::isValidBigram(*outProbability)) {
+        // This bigram is too weak to output.
+        *outBigramPos = NOT_A_DICT_POS;
+    } else {
+        *outBigramPos = followBigramLinkAndGetCurrentBigramPtNodePos(originalBigramPos);
+    }
     if (usesAdditionalBuffer) {
         *bigramEntryPos += mBuffer->getOriginalBufferSize();
     }
@@ -153,15 +158,21 @@
         const int bigramTargetNodePos =
                 followBigramLinkAndGetCurrentBigramPtNodePos(originalBigramPos);
         nodeReader.fetchNodeInfoInBufferFromPtNodePos(bigramTargetNodePos);
-        // TODO: Update probability for supporting probability decaying.
         if (nodeReader.isDeleted() || !nodeReader.isTerminal()
                 || bigramTargetNodePos == NOT_A_DICT_POS) {
             // The target is no longer valid terminal. Invalidate the current bigram entry.
             if (!BigramListReadWriteUtils::writeBigramEntry(mBuffer, bigramFlags,
-                    NOT_A_DICT_POS /* targetOffset */, &bigramEntryPos)) {
+                    NOT_A_DICT_POS /* targetPtNodePos */, &bigramEntryPos)) {
                 return false;
             }
-        } else {
+            continue;
+        }
+        bool isRemoved = false;
+        if (!updateProbabilityForDecay(bigramFlags, bigramTargetNodePos, &bigramEntryPos,
+                &isRemoved)) {
+            return false;
+        }
+        if (!isRemoved) {
             (*outValidBigramEntryCount) += 1;
         }
     } while(BigramListReadWriteUtils::hasNext(bigramFlags));
@@ -247,8 +258,14 @@
         if (followBigramLinkAndGetCurrentBigramPtNodePos(originalBigramPos) == bigramTargetPos) {
             // Update this bigram entry.
             *outAddedNewBigram = false;
+            const int originalProbability = BigramListReadWriteUtils::getProbabilityFromFlags(
+                    bigramFlags);
+            const int probabilityToWrite = mIsDecayingDict ?
+                    DecayingUtils::getUpdatedBigramProbabilityDelta(
+                            originalProbability, probability) : probability;
             const BigramListReadWriteUtils::BigramFlags updatedFlags =
-                    BigramListReadWriteUtils::setProbabilityInFlags(bigramFlags, probability);
+                    BigramListReadWriteUtils::setProbabilityInFlags(bigramFlags,
+                            probabilityToWrite);
             return BigramListReadWriteUtils::writeBigramEntry(mBuffer, updatedFlags,
                     originalBigramPos, &entryPos);
         }
@@ -276,8 +293,11 @@
 bool DynamicBigramListPolicy::writeNewBigramEntry(const int bigramTargetPos, const int probability,
         int *const writingPos) {
     // hasNext is false because we are adding a new bigram entry at the end of the bigram list.
+    const int probabilityToWrite = mIsDecayingDict ?
+            DecayingUtils::getUpdatedBigramProbabilityDelta(NOT_A_PROBABILITY, probability) :
+                    probability;
     return BigramListReadWriteUtils::createAndWriteBigramEntry(mBuffer, bigramTargetPos,
-            probability, false /* hasNext */, writingPos);
+            probabilityToWrite, false /* hasNext */, writingPos);
 }
 
 bool DynamicBigramListPolicy::removeBigram(const int bigramListPos, const int bigramTargetPos) {
@@ -339,4 +359,33 @@
     return currentPos;
 }
 
+bool DynamicBigramListPolicy::updateProbabilityForDecay(
+        BigramListReadWriteUtils::BigramFlags bigramFlags, const int targetPtNodePos,
+        int *const bigramEntryPos, bool *const outRemoved) const {
+    *outRemoved = false;
+    if (mIsDecayingDict) {
+        // Update bigram probability for decaying.
+        const int newProbability = DecayingUtils::getBigramProbabilityDeltaToSave(
+                BigramListReadWriteUtils::getProbabilityFromFlags(bigramFlags));
+        if (DecayingUtils::isValidBigram(newProbability)) {
+            // Write new probability.
+            const BigramListReadWriteUtils::BigramFlags updatedBigramFlags =
+                    BigramListReadWriteUtils::setProbabilityInFlags(
+                            bigramFlags, newProbability);
+            if (!BigramListReadWriteUtils::writeBigramEntry(mBuffer, updatedBigramFlags,
+                    targetPtNodePos, bigramEntryPos)) {
+                return false;
+            }
+        } else {
+            // Remove current bigram entry.
+            *outRemoved = true;
+            if (!BigramListReadWriteUtils::writeBigramEntry(mBuffer, bigramFlags,
+                    NOT_A_DICT_POS /* targetPtNodePos */, bigramEntryPos)) {
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
 } // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.h b/native/jni/src/suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.h
index 3ebf699..b358b4e 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/bigram/dynamic_bigram_list_policy.h
@@ -21,6 +21,7 @@
 
 #include "defines.h"
 #include "suggest/core/policy/dictionary_bigrams_structure_policy.h"
+#include "suggest/policyimpl/dictionary/bigram/bigram_list_read_write_utils.h"
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h"
 
 namespace latinime {
@@ -34,8 +35,9 @@
 class DynamicBigramListPolicy : public DictionaryBigramsStructurePolicy {
  public:
     DynamicBigramListPolicy(BufferWithExtendableBuffer *const buffer,
-            const DictionaryShortcutsStructurePolicy *const shortcutPolicy)
-            : mBuffer(buffer), mShortcutPolicy(shortcutPolicy) {}
+            const DictionaryShortcutsStructurePolicy *const shortcutPolicy,
+            const bool isDecayingDict)
+            : mBuffer(buffer), mShortcutPolicy(shortcutPolicy), mIsDecayingDict(isDecayingDict) {}
 
     ~DynamicBigramListPolicy() {}
 
@@ -74,9 +76,13 @@
 
     BufferWithExtendableBuffer *const mBuffer;
     const DictionaryShortcutsStructurePolicy *const mShortcutPolicy;
+    const bool mIsDecayingDict;
 
     // Follow bigram link and return the position of bigram target PtNode that is currently valid.
     int followBigramLinkAndGetCurrentBigramPtNodePos(const int originalBigramPos) const;
+
+    bool updateProbabilityForDecay(BigramListReadWriteUtils::BigramFlags bigramFlags,
+            const int targetPtNodePos, int *const bigramEntryPos, bool *const outRemoved) const;
 };
 } // namespace latinime
 #endif // LATINIME_DYNAMIC_BIGRAM_LIST_POLICY_H
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.cpp b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.cpp
index 5eb4733..081163a 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.cpp
@@ -16,6 +16,8 @@
 
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.h"
 
+#include "suggest/policyimpl/dictionary/utils/decaying_utils.h"
+
 namespace latinime {
 
 bool DynamicPatriciaTrieGcEventListeners
@@ -25,6 +27,19 @@
     // PtNode is useless when the PtNode is not a terminal and doesn't have any not useless
     // children.
     bool isUselessPtNode = !node->isTerminal();
+    if (node->isTerminal() && mIsDecayingDict) {
+        const int newProbability =
+                DecayingUtils::getUnigramProbabilityToSave(node->getProbability());
+        int writingPos = node->getProbabilityFieldPos();
+        // Update probability.
+        if (!DynamicPatriciaTrieWritingUtils::writeProbabilityAndAdvancePosition(
+                mBuffer, newProbability, &writingPos)) {
+            return false;
+        }
+        if (!DecayingUtils::isValidUnigram(newProbability)) {
+            isUselessPtNode = false;
+        }
+    }
     if (mChildrenValue > 0) {
         isUselessPtNode = false;
     } else if (node->isTerminal()) {
@@ -41,7 +56,7 @@
             return false;
         }
     } else {
-        valueStack.back() += 1;
+        mValueStack.back() += 1;
         if (node->isTerminal()) {
             mValidUnigramCount += 1;
         }
@@ -49,6 +64,23 @@
     return true;
 }
 
+bool DynamicPatriciaTrieGcEventListeners::TraversePolicyToUpdateBigramProbability
+        ::onVisitingPtNode(const DynamicPatriciaTrieNodeReader *const node,
+                const int *const nodeCodePoints) {
+    if (!node->isDeleted()) {
+        int pos = node->getBigramsPos();
+        if (pos != NOT_A_DICT_POS) {
+            int bigramEntryCount = 0;
+            if (!mBigramPolicy->updateAllBigramEntriesAndDeleteUselessEntries(&pos,
+                    &bigramEntryCount)) {
+                return false;
+            }
+            mValidBigramEntryCount += bigramEntryCount;
+        }
+    }
+    return true;
+}
+
 // Writes dummy PtNode array size when the head of PtNode array is read.
 bool DynamicPatriciaTrieGcEventListeners::TraversePolicyToPlaceAndWriteValidPtNodesToBuffer
         ::onDescend(const int ptNodeArrayPos) {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.h b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.h
index aa6e609..463715a 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_gc_event_listeners.h
@@ -39,23 +39,23 @@
      public:
         TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted(
                 DynamicPatriciaTrieWritingHelper *const writingHelper,
-                BufferWithExtendableBuffer *const buffer)
-                : mWritingHelper(writingHelper), mBuffer(buffer), valueStack(),
-                  mChildrenValue(0), mValidUnigramCount(0) {}
+                BufferWithExtendableBuffer *const buffer, const bool isDecayingDict)
+                : mWritingHelper(writingHelper), mBuffer(buffer), mIsDecayingDict(isDecayingDict),
+                  mValueStack(), mChildrenValue(0), mValidUnigramCount(0) {}
 
         ~TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted() {};
 
         bool onAscend() {
-            if (valueStack.empty()) {
+            if (mValueStack.empty()) {
                 return false;
             }
-            mChildrenValue = valueStack.back();
-            valueStack.pop_back();
+            mChildrenValue = mValueStack.back();
+            mValueStack.pop_back();
             return true;
         }
 
         bool onDescend(const int ptNodeArrayPos) {
-            valueStack.push_back(0);
+            mValueStack.push_back(0);
             return true;
         }
 
@@ -74,7 +74,8 @@
 
         DynamicPatriciaTrieWritingHelper *const mWritingHelper;
         BufferWithExtendableBuffer *const mBuffer;
-        std::vector<int> valueStack;
+        const int mIsDecayingDict;
+        std::vector<int> mValueStack;
         int mChildrenValue;
         int mValidUnigramCount;
     };
@@ -94,20 +95,7 @@
         bool onReadingPtNodeArrayTail() { return true; }
 
         bool onVisitingPtNode(const DynamicPatriciaTrieNodeReader *const node,
-                const int *const nodeCodePoints) {
-            if (!node->isDeleted()) {
-                int pos = node->getBigramsPos();
-                if (pos != NOT_A_DICT_POS) {
-                    int bigramEntryCount = 0;
-                    if (!mBigramPolicy->updateAllBigramEntriesAndDeleteUselessEntries(&pos,
-                            &bigramEntryCount)) {
-                        return false;
-                    }
-                    mValidBigramEntryCount += bigramEntryCount;
-                }
-            }
-            return true;
-        }
+                const int *const nodeCodePoints);
 
         int getValidBigramEntryCount() const {
             return mValidBigramEntryCount;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp
index 4581ec0..0d8c927 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp
@@ -18,6 +18,7 @@
 
 #include <cstdio>
 #include <cstring>
+#include <ctime>
 
 #include "defines.h"
 #include "suggest/core/dicnode/dic_node.h"
@@ -27,12 +28,17 @@
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_reading_utils.h"
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h"
 #include "suggest/policyimpl/dictionary/patricia_trie_reading_utils.h"
+#include "suggest/policyimpl/dictionary/utils/decaying_utils.h"
 #include "suggest/policyimpl/dictionary/utils/probability_utils.h"
 
 namespace latinime {
 
 const char *const DynamicPatriciaTriePolicy::UNIGRAM_COUNT_QUERY = "UNIGRAM_COUNT";
 const char *const DynamicPatriciaTriePolicy::BIGRAM_COUNT_QUERY = "BIGRAM_COUNT";
+const int DynamicPatriciaTriePolicy::MAX_DICT_EXTENDED_REGION_SIZE = 1024 * 1024;
+const int DynamicPatriciaTriePolicy::MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS =
+        DynamicPatriciaTrieWritingHelper::MAX_DICTIONARY_SIZE - 1024;
+const int DynamicPatriciaTriePolicy::MIN_SECONDS_TO_REQUIRE_GC_WHEN_WRITING = 2 * 60 * 60;
 
 void DynamicPatriciaTriePolicy::createAndGetAllChildNodes(const DicNode *const dicNode,
         DicNodeVector *const childDicNodes) const {
@@ -143,14 +149,17 @@
 
 int DynamicPatriciaTriePolicy::getProbability(const int unigramProbability,
         const int bigramProbability) const {
-    // TODO: check mHeaderPolicy.usesForgettingCurve();
-    if (unigramProbability == NOT_A_PROBABILITY) {
-        return NOT_A_PROBABILITY;
-    } else if (bigramProbability == NOT_A_PROBABILITY) {
-        return ProbabilityUtils::backoff(unigramProbability);
+    if (mHeaderPolicy.isDecayingDict()) {
+        return DecayingUtils::getProbability(unigramProbability, bigramProbability);
     } else {
-        return ProbabilityUtils::computeProbabilityForBigram(unigramProbability,
-                bigramProbability);
+        if (unigramProbability == NOT_A_PROBABILITY) {
+            return NOT_A_PROBABILITY;
+        } else if (bigramProbability == NOT_A_PROBABILITY) {
+            return ProbabilityUtils::backoff(unigramProbability);
+        } else {
+            return ProbabilityUtils::computeProbabilityForBigram(unigramProbability,
+                    bigramProbability);
+        }
     }
 }
 
@@ -199,11 +208,16 @@
         AKLOGI("Warning: addUnigramWord() is called for non-updatable dictionary.");
         return false;
     }
+    if (mBufferWithExtendableBuffer.getTailPosition()
+            >= MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS) {
+        AKLOGE("The dictionary is too large to dynamically update.");
+        return false;
+    }
     DynamicPatriciaTrieReadingHelper readingHelper(&mBufferWithExtendableBuffer,
             getBigramsStructurePolicy(), getShortcutsStructurePolicy());
     readingHelper.initWithPtNodeArrayPos(getRootPosition());
     DynamicPatriciaTrieWritingHelper writingHelper(&mBufferWithExtendableBuffer,
-            &mBigramListPolicy, &mShortcutListPolicy);
+            &mBigramListPolicy, &mShortcutListPolicy, mHeaderPolicy.isDecayingDict());
     bool addedNewUnigram = false;
     if (writingHelper.addUnigramWord(&readingHelper, word, length, probability,
             &addedNewUnigram)) {
@@ -222,6 +236,11 @@
         AKLOGI("Warning: addBigramWords() is called for non-updatable dictionary.");
         return false;
     }
+    if (mBufferWithExtendableBuffer.getTailPosition()
+            >= MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS) {
+        AKLOGE("The dictionary is too large to dynamically update.");
+        return false;
+    }
     const int word0Pos = getTerminalNodePositionOfWord(word0, length0,
             false /* forceLowerCaseSearch */);
     if (word0Pos == NOT_A_DICT_POS) {
@@ -233,7 +252,7 @@
         return false;
     }
     DynamicPatriciaTrieWritingHelper writingHelper(&mBufferWithExtendableBuffer,
-            &mBigramListPolicy, &mShortcutListPolicy);
+            &mBigramListPolicy, &mShortcutListPolicy, mHeaderPolicy.isDecayingDict());
     bool addedNewBigram = false;
     if (writingHelper.addBigramWords(word0Pos, word1Pos, probability, &addedNewBigram)) {
         if (addedNewBigram) {
@@ -251,6 +270,11 @@
         AKLOGI("Warning: removeBigramWords() is called for non-updatable dictionary.");
         return false;
     }
+    if (mBufferWithExtendableBuffer.getTailPosition()
+            >= MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS) {
+        AKLOGE("The dictionary is too large to dynamically update.");
+        return false;
+    }
     const int word0Pos = getTerminalNodePositionOfWord(word0, length0,
             false /* forceLowerCaseSearch */);
     if (word0Pos == NOT_A_DICT_POS) {
@@ -262,7 +286,7 @@
         return false;
     }
     DynamicPatriciaTrieWritingHelper writingHelper(&mBufferWithExtendableBuffer,
-            &mBigramListPolicy, &mShortcutListPolicy);
+            &mBigramListPolicy, &mShortcutListPolicy, mHeaderPolicy.isDecayingDict());
     if (writingHelper.removeBigramWords(word0Pos, word1Pos)) {
         mBigramCount--;
         return true;
@@ -277,7 +301,7 @@
         return;
     }
     DynamicPatriciaTrieWritingHelper writingHelper(&mBufferWithExtendableBuffer,
-            &mBigramListPolicy, &mShortcutListPolicy);
+            &mBigramListPolicy, &mShortcutListPolicy, mHeaderPolicy.isDecayingDict());
     writingHelper.writeToDictFile(filePath, &mHeaderPolicy, mUnigramCount, mBigramCount);
 }
 
@@ -287,17 +311,42 @@
         return;
     }
     DynamicPatriciaTrieWritingHelper writingHelper(&mBufferWithExtendableBuffer,
-            &mBigramListPolicy, &mShortcutListPolicy);
+            &mBigramListPolicy, &mShortcutListPolicy, mHeaderPolicy.isDecayingDict());
     writingHelper.writeToDictFileWithGC(getRootPosition(), filePath, &mHeaderPolicy);
 }
 
-bool DynamicPatriciaTriePolicy::needsToRunGC() const {
+bool DynamicPatriciaTriePolicy::needsToRunGC(const bool mindsBlockByGC) const {
     if (!mBuffer->isUpdatable()) {
         AKLOGI("Warning: needsToRunGC() is called for non-updatable dictionary.");
         return false;
     }
-    // TODO: Implement more properly.
-    return mBufferWithExtendableBuffer.isNearSizeLimit();
+    if (mBufferWithExtendableBuffer.isNearSizeLimit()) {
+        // Additional buffer size is near the limit.
+        return true;
+    } else if (mHeaderPolicy.getExtendedRegionSize()
+            + mBufferWithExtendableBuffer.getUsedAdditionalBufferSize()
+                    > MAX_DICT_EXTENDED_REGION_SIZE) {
+        // Total extended region size exceeds the limit.
+        return true;
+    } else if (mBufferWithExtendableBuffer.getTailPosition()
+            >= MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS
+                    && mBufferWithExtendableBuffer.getUsedAdditionalBufferSize() > 0) {
+        // Needs to reduce dictionary size.
+        return true;
+    } else if (mHeaderPolicy.isDecayingDict()) {
+        if (mUnigramCount >= DecayingUtils::MAX_UNIGRAM_COUNT) {
+            // Unigram count exceeds the limit.
+            return true;
+        } else if (mBigramCount >= DecayingUtils::MAX_BIGRAM_COUNT) {
+            // Bigram count exceeds the limit.
+            return true;
+        } else if (mindsBlockByGC && mHeaderPolicy.getLastUpdatedTime()
+                + MIN_SECONDS_TO_REQUIRE_GC_WHEN_WRITING < time(0)) {
+            // Time to update probabilities for decaying.
+            return true;
+        }
+    }
+    return false;
 }
 
 void DynamicPatriciaTriePolicy::getProperty(const char *const query, char *const outResult,
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.h b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.h
index 7f9d4d9..d3150c6 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.h
@@ -37,7 +37,8 @@
               mBufferWithExtendableBuffer(mBuffer->getBuffer() + mHeaderPolicy.getSize(),
                       mBuffer->getBufferSize() - mHeaderPolicy.getSize()),
               mShortcutListPolicy(&mBufferWithExtendableBuffer),
-              mBigramListPolicy(&mBufferWithExtendableBuffer, &mShortcutListPolicy),
+              mBigramListPolicy(&mBufferWithExtendableBuffer, &mShortcutListPolicy,
+                      mHeaderPolicy.isDecayingDict()),
               mUnigramCount(mHeaderPolicy.getUnigramCount()),
               mBigramCount(mHeaderPolicy.getBigramCount()) {}
 
@@ -91,7 +92,7 @@
 
     void flushWithGC(const char *const filePath);
 
-    bool needsToRunGC() const;
+    bool needsToRunGC(const bool mindsBlockByGC) const;
 
     void getProperty(const char *const query, char *const outResult,
             const int maxResultLength) const;
@@ -101,6 +102,9 @@
 
     static const char*const UNIGRAM_COUNT_QUERY;
     static const char*const BIGRAM_COUNT_QUERY;
+    static const int MAX_DICT_EXTENDED_REGION_SIZE;
+    static const int MIN_DICT_SIZE_TO_REFUSE_DYNAMIC_OPERATIONS;
+    static const int MIN_SECONDS_TO_REQUIRE_GC_WHEN_WRITING;
 
     const MmappedBuffer *const mBuffer;
     const HeaderPolicy mHeaderPolicy;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.cpp b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.cpp
index bae5e8c..28124d2 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.cpp
@@ -25,6 +25,7 @@
 #include "suggest/policyimpl/dictionary/header/header_policy.h"
 #include "suggest/policyimpl/dictionary/patricia_trie_reading_utils.h"
 #include "suggest/policyimpl/dictionary/shortcut/dynamic_shortcut_list_policy.h"
+#include "suggest/policyimpl/dictionary/utils/decaying_utils.h"
 #include "suggest/policyimpl/dictionary/utils/dict_file_writing_utils.h"
 #include "utils/hash_map_compat.h"
 
@@ -57,7 +58,9 @@
                     wordCodePoints[matchedCodePointCount + j])) {
                 *outAddedNewUnigram = true;
                 return reallocatePtNodeAndAddNewPtNodes(nodeReader,
-                        readingHelper->getMergedNodeCodePoints(), j, probability,
+                        readingHelper->getMergedNodeCodePoints(), j,
+                        getUpdatedProbability(NOT_A_PROBABILITY /* originalProbability */,
+                                probability),
                         wordCodePoints + matchedCodePointCount,
                         codePointCount - matchedCodePointCount);
             }
@@ -69,7 +72,8 @@
         }
         if (!nodeReader->hasChildren()) {
             *outAddedNewUnigram = true;
-            return createChildrenPtNodeArrayAndAChildPtNode(nodeReader, probability,
+            return createChildrenPtNodeArrayAndAChildPtNode(nodeReader,
+                    getUpdatedProbability(NOT_A_PROBABILITY /* originalProbability */, probability),
                     wordCodePoints + readingHelper->getTotalCodePointCount(),
                     codePointCount - readingHelper->getTotalCodePointCount());
         }
@@ -86,7 +90,7 @@
     return createAndInsertNodeIntoPtNodeArray(parentPos,
             wordCodePoints + readingHelper->getPrevTotalCodePointCount(),
             codePointCount - readingHelper->getPrevTotalCodePointCount(),
-            probability, &pos);
+            getUpdatedProbability(NOT_A_PROBABILITY /* originalProbability */, probability), &pos);
 }
 
 bool DynamicPatriciaTrieWritingHelper::addBigramWords(const int word0Pos, const int word1Pos,
@@ -147,7 +151,7 @@
         const HeaderPolicy *const headerPolicy, const int unigramCount, const int bigramCount) {
     BufferWithExtendableBuffer headerBuffer(0 /* originalBuffer */, 0 /* originalBufferSize */);
     const int extendedRegionSize = headerPolicy->getExtendedRegionSize() +
-            mBuffer->getTailPosition() - mBuffer->getOriginalBufferSize();
+            mBuffer->getUsedAdditionalBufferSize();
     if (!headerPolicy->writeHeaderToBuffer(&headerBuffer, false /* updatesLastUpdatedTime */,
             unigramCount, bigramCount, extendedRegionSize)) {
         return;
@@ -351,9 +355,11 @@
     if (originalPtNode->isTerminal()) {
         // Overwrites the probability.
         *outAddedNewUnigram = false;
+        const int probabilityToWrite = getUpdatedProbability(originalPtNode->getProbability(),
+                probability);
         int probabilityFieldPos = originalPtNode->getProbabilityFieldPos();
         if (!DynamicPatriciaTrieWritingUtils::writeProbabilityAndAdvancePosition(mBuffer,
-                probability, &probabilityFieldPos)) {
+                probabilityToWrite, &probabilityFieldPos)) {
             return false;
         }
     } else {
@@ -365,7 +371,8 @@
         }
         if (!writePtNodeToBufferByCopyingPtNodeInfo(mBuffer, originalPtNode,
                 originalPtNode->getParentPos(), codePoints, originalPtNode->getCodePointCount(),
-                probability, &movedPos)) {
+                getUpdatedProbability(NOT_A_PROBABILITY /* originalProbability */, probability),
+                &movedPos)) {
             return false;
         }
     }
@@ -481,11 +488,15 @@
     DynamicPatriciaTrieGcEventListeners
             ::TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
                     traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted(
-                            this, mBuffer);
+                            this, mBuffer, mIsDecayingDict);
     if (!readingHelper.traverseAllPtNodesInPostorderDepthFirstManner(
             &traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted)) {
         return false;
     }
+    if (mIsDecayingDict && traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
+            .getValidUnigramCount() > DecayingUtils::MAX_UNIGRAM_COUNT_AFTER_GC) {
+        // TODO: Remove more unigrams.
+    }
 
     readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
     DynamicPatriciaTrieGcEventListeners::TraversePolicyToUpdateBigramProbability
@@ -495,6 +506,11 @@
         return false;
     }
 
+    if (mIsDecayingDict && traversePolicyToUpdateBigramProbability.getValidBigramEntryCount()
+            > DecayingUtils::MAX_BIGRAM_COUNT_AFTER_GC) {
+        // TODO: Remove more bigrams.
+    }
+
     // Mapping from positions in mBuffer to positions in bufferToWrite.
     DictPositionRelocationMap dictPositionRelocationMap;
     readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
@@ -508,7 +524,8 @@
 
     // Create policy instance for the GCed dictionary.
     DynamicShortcutListPolicy newDictShortcutPolicy(bufferToWrite);
-    DynamicBigramListPolicy newDictBigramPolicy(bufferToWrite, &newDictShortcutPolicy);
+    DynamicBigramListPolicy newDictBigramPolicy(bufferToWrite, &newDictShortcutPolicy,
+            mIsDecayingDict);
     // Create reading helper for the GCed dictionary.
     DynamicPatriciaTrieReadingHelper newDictReadingHelper(bufferToWrite, &newDictBigramPolicy,
             &newDictShortcutPolicy);
@@ -525,4 +542,13 @@
     return true;
 }
 
+int DynamicPatriciaTrieWritingHelper::getUpdatedProbability(const int originalProbability,
+        const int newProbability) {
+    if (mIsDecayingDict) {
+        return DecayingUtils::getUpdatedUnigramProbability(originalProbability, newProbability);
+    } else {
+        return newProbability;
+    }
+}
+
 } // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h
index 827b609..ecee2cd 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h
@@ -47,10 +47,13 @@
         DISALLOW_COPY_AND_ASSIGN(DictPositionRelocationMap);
     };
 
+    static const size_t MAX_DICTIONARY_SIZE;
+
     DynamicPatriciaTrieWritingHelper(BufferWithExtendableBuffer *const buffer,
             DynamicBigramListPolicy *const bigramPolicy,
-            DynamicShortcutListPolicy *const shortcutPolicy)
-            : mBuffer(buffer), mBigramPolicy(bigramPolicy), mShortcutPolicy(shortcutPolicy) {}
+            DynamicShortcutListPolicy *const shortcutPolicy, const bool isDecayingDict)
+            : mBuffer(buffer), mBigramPolicy(bigramPolicy), mShortcutPolicy(shortcutPolicy),
+              mIsDecayingDict(isDecayingDict) {}
 
     ~DynamicPatriciaTrieWritingHelper() {}
 
@@ -87,11 +90,11 @@
     DISALLOW_IMPLICIT_CONSTRUCTORS(DynamicPatriciaTrieWritingHelper);
 
     static const int CHILDREN_POSITION_FIELD_SIZE;
-    static const size_t MAX_DICTIONARY_SIZE;
 
     BufferWithExtendableBuffer *const mBuffer;
     DynamicBigramListPolicy *const mBigramPolicy;
     DynamicShortcutListPolicy *const mShortcutPolicy;
+    const bool mIsDecayingDict;
 
     bool markNodeAsMovedAndSetPosition(const DynamicPatriciaTrieNodeReader *const nodeToUpdate,
             const int movedPos, const int bigramLinkedNodePos);
@@ -127,6 +130,8 @@
 
     bool runGC(const int rootPtNodeArrayPos, BufferWithExtendableBuffer *const bufferToWrite,
             int *const outUnigramCount, int *const outBigramCount);
+
+    int getUpdatedProbability(const int originalProbability, const int newProbability);
 };
 } // namespace latinime
 #endif /* LATINIME_DYNAMIC_PATRICIA_TRIE_WRITING_HELPER_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
index 78c6c04..9ce9994 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
@@ -20,7 +20,8 @@
 
 // Note that these are corresponding definitions in Java side in FormatSpec.FileHeader.
 const char *const HeaderPolicy::MULTIPLE_WORDS_DEMOTION_RATE_KEY = "MULTIPLE_WORDS_DEMOTION_RATE";
-const char *const HeaderPolicy::USES_FORGETTING_CURVE_KEY = "USES_FORGETTING_CURVE";
+// TODO: Change attribute string to "IS_DECAYING_DICT".
+const char *const HeaderPolicy::IS_DECAYING_DICT_KEY = "USES_FORGETTING_CURVE";
 const char *const HeaderPolicy::LAST_UPDATED_TIME_KEY = "date";
 const char *const HeaderPolicy::UNIGRAM_COUNT_KEY = "UNIGRAM_COUNT";
 const char *const HeaderPolicy::BIGRAM_COUNT_KEY = "BIGRAM_COUNT";
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
index 93b9c6f..4261667 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
@@ -36,8 +36,8 @@
               mSize(HeaderReadWriteUtils::getHeaderSize(dictBuf)),
               mAttributeMap(createAttributeMapAndReadAllAttributes(dictBuf)),
               mMultiWordCostMultiplier(readMultipleWordCostMultiplier()),
-              mUsesForgettingCurve(HeaderReadWriteUtils::readBoolAttributeValue(&mAttributeMap,
-                      USES_FORGETTING_CURVE_KEY, false /* defaultValue */)),
+              mIsDecayingDict(HeaderReadWriteUtils::readBoolAttributeValue(&mAttributeMap,
+                      IS_DECAYING_DICT_KEY, false /* defaultValue */)),
               mLastUpdatedTime(HeaderReadWriteUtils::readIntAttributeValue(&mAttributeMap,
                       LAST_UPDATED_TIME_KEY, time(0) /* defaultValue */)),
               mUnigramCount(HeaderReadWriteUtils::readIntAttributeValue(&mAttributeMap,
@@ -54,8 +54,8 @@
               mDictionaryFlags(HeaderReadWriteUtils::createAndGetDictionaryFlagsUsingAttributeMap(
                       attributeMap)), mSize(0), mAttributeMap(*attributeMap),
               mMultiWordCostMultiplier(readMultipleWordCostMultiplier()),
-              mUsesForgettingCurve(HeaderReadWriteUtils::readBoolAttributeValue(&mAttributeMap,
-                      USES_FORGETTING_CURVE_KEY, false /* defaultValue */)),
+              mIsDecayingDict(HeaderReadWriteUtils::readBoolAttributeValue(&mAttributeMap,
+                      IS_DECAYING_DICT_KEY, false /* defaultValue */)),
               mLastUpdatedTime(HeaderReadWriteUtils::readIntAttributeValue(&mAttributeMap,
                       LAST_UPDATED_TIME_KEY, time(0) /* defaultValue */)),
               mUnigramCount(0), mBigramCount(0), mExtendedRegionSize(0) {}
@@ -82,8 +82,8 @@
         return mMultiWordCostMultiplier;
     }
 
-    AK_FORCE_INLINE bool usesForgettingCurve() const {
-        return mUsesForgettingCurve;
+    AK_FORCE_INLINE bool isDecayingDict() const {
+        return mIsDecayingDict;
     }
 
     AK_FORCE_INLINE int getLastUpdatedTime() const {
@@ -113,7 +113,7 @@
     DISALLOW_IMPLICIT_CONSTRUCTORS(HeaderPolicy);
 
     static const char *const MULTIPLE_WORDS_DEMOTION_RATE_KEY;
-    static const char *const USES_FORGETTING_CURVE_KEY;
+    static const char *const IS_DECAYING_DICT_KEY;
     static const char *const LAST_UPDATED_TIME_KEY;
     static const char *const UNIGRAM_COUNT_KEY;
     static const char *const BIGRAM_COUNT_KEY;
@@ -126,7 +126,7 @@
     const int mSize;
     HeaderReadWriteUtils::AttributeMap mAttributeMap;
     const float mMultiWordCostMultiplier;
-    const bool mUsesForgettingCurve;
+    const bool mIsDecayingDict;
     const int mLastUpdatedTime;
     const int mUnigramCount;
     const int mBigramCount;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/patricia_trie_policy.h b/native/jni/src/suggest/policyimpl/dictionary/patricia_trie_policy.h
index 4277ff5..8d88c68 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/patricia_trie_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/patricia_trie_policy.h
@@ -107,7 +107,7 @@
         AKLOGI("Warning: flushWithGC() is called for non-updatable dictionary.");
     }
 
-    bool needsToRunGC() const {
+    bool needsToRunGC(const bool mindsBlockByGC) const {
         // This method should not be called for non-updatable dictionary.
         AKLOGI("Warning: needsToRunGC() is called for non-updatable dictionary.");
         return false;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h b/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h
index 17d2e39..9dc3482 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h
@@ -42,6 +42,10 @@
         return mOriginalBufferSize + mUsedAdditionalBufferSize;
     }
 
+    AK_FORCE_INLINE int getUsedAdditionalBufferSize() const {
+        return mUsedAdditionalBufferSize;
+    }
+
     /**
      * For reading.
      */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/decaying_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/decaying_utils.cpp
new file mode 100644
index 0000000..942a742
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/decaying_utils.cpp
@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "suggest/policyimpl/dictionary/utils/decaying_utils.h"
+
+#include "suggest/policyimpl/dictionary/utils/probability_utils.h"
+
+namespace latinime {
+
+const int DecayingUtils::MAX_UNIGRAM_COUNT = 12000;
+const int DecayingUtils::MAX_UNIGRAM_COUNT_AFTER_GC = 10000;
+const int DecayingUtils::MAX_BIGRAM_COUNT = 12000;
+const int DecayingUtils::MAX_BIGRAM_COUNT_AFTER_GC = 10000;
+
+const int DecayingUtils::MAX_COMPUTED_PROBABILITY = 127;
+const int DecayingUtils::MAX_UNIGRAM_PROBABILITY = 120;
+const int DecayingUtils::MIN_VALID_UNIGRAM_PROBABILITY = 24;
+const int DecayingUtils::UNIGRAM_PROBABILITY_STEP = 8;
+const int DecayingUtils::MAX_BIGRAM_PROBABILITY_DELTA = 15;
+const int DecayingUtils::MIN_VALID_BIGRAM_PROBABILITY_DELTA = 3;
+const int DecayingUtils::BIGRAM_PROBABILITY_DELTA_STEP = 1;
+
+/* static */ int DecayingUtils::getProbability(const int encodedUnigramProbability,
+        const int encodedBigramProbabilityDelta) {
+    if (encodedUnigramProbability == NOT_A_PROBABILITY) {
+        return NOT_A_PROBABILITY;
+    } else if (encodedBigramProbabilityDelta == NOT_A_PROBABILITY) {
+        const int rawProbability = ProbabilityUtils::backoff(decodeUnigramProbability(
+                encodedUnigramProbability));
+        return min(getDecayedProbability(rawProbability), MAX_COMPUTED_PROBABILITY);
+    } else {
+        const int rawProbability = ProbabilityUtils::computeProbabilityForBigram(
+                decodeUnigramProbability(encodedUnigramProbability),
+                decodeBigramProbabilityDelta(encodedBigramProbabilityDelta));
+        return min(getDecayedProbability(rawProbability), MAX_COMPUTED_PROBABILITY);
+    }
+}
+
+/* static */ int DecayingUtils::getUpdatedUnigramProbability(const int originalEncodedProbability,
+        const int newProbability) {
+    if (originalEncodedProbability == NOT_A_PROBABILITY) {
+        // The unigram is not in this dictionary.
+        if (newProbability == NOT_A_PROBABILITY) {
+            // The unigram is not in other dictionaries.
+            return 0;
+        } else {
+            return MIN_VALID_UNIGRAM_PROBABILITY;
+        }
+    } else {
+        if (newProbability != NOT_A_PROBABILITY
+                && originalEncodedProbability < MIN_VALID_UNIGRAM_PROBABILITY) {
+            return MIN_VALID_UNIGRAM_PROBABILITY;
+        }
+        return min(originalEncodedProbability + UNIGRAM_PROBABILITY_STEP, MAX_UNIGRAM_PROBABILITY);
+    }
+}
+
+/* static */ int DecayingUtils::getUnigramProbabilityToSave(const int encodedProbability) {
+    return max(encodedProbability - UNIGRAM_PROBABILITY_STEP, 0);
+}
+
+/* static */ int DecayingUtils::getBigramProbabilityDeltaToSave(const int encodedProbabilityDelta) {
+    return max(encodedProbabilityDelta - BIGRAM_PROBABILITY_DELTA_STEP, 0);
+}
+
+/* static */ int DecayingUtils::getUpdatedBigramProbabilityDelta(
+        const int originalEncodedProbabilityDelta, const int newProbability) {
+    if (originalEncodedProbabilityDelta == NOT_A_PROBABILITY) {
+        // The bigram relation is not in this dictionary.
+        if (newProbability == NOT_A_PROBABILITY) {
+            // The bigram target is not in other dictionaries.
+            return 0;
+        } else {
+            return MIN_VALID_BIGRAM_PROBABILITY_DELTA;
+        }
+    } else {
+        if (newProbability != NOT_A_PROBABILITY
+                && originalEncodedProbabilityDelta < MIN_VALID_BIGRAM_PROBABILITY_DELTA) {
+            return MIN_VALID_BIGRAM_PROBABILITY_DELTA;
+        }
+        return min(originalEncodedProbabilityDelta + BIGRAM_PROBABILITY_DELTA_STEP,
+                MAX_BIGRAM_PROBABILITY_DELTA);
+    }
+}
+
+/* static */ int DecayingUtils::isValidUnigram(const int encodedUnigramProbability) {
+    return encodedUnigramProbability >= MIN_VALID_UNIGRAM_PROBABILITY;
+}
+
+/* static */ int DecayingUtils::isValidBigram(const int encodedBigramProbabilityDelta) {
+    return encodedBigramProbabilityDelta >= MIN_VALID_BIGRAM_PROBABILITY_DELTA;
+}
+
+/* static */ int DecayingUtils::decodeUnigramProbability(const int encodedProbability) {
+    const int probability = encodedProbability - MIN_VALID_UNIGRAM_PROBABILITY;
+    if (probability < 0) {
+        return NOT_A_PROBABILITY;
+    } else {
+        return min(probability, MAX_UNIGRAM_PROBABILITY);
+    }
+}
+
+/* static */ int DecayingUtils::decodeBigramProbabilityDelta(const int encodedProbabilityDelta) {
+    const int probabilityDelta = encodedProbabilityDelta - MIN_VALID_BIGRAM_PROBABILITY_DELTA;
+    if (probabilityDelta < 0) {
+        return NOT_A_PROBABILITY;
+    } else {
+        return min(probabilityDelta, MAX_BIGRAM_PROBABILITY_DELTA);
+    }
+}
+
+/* static */ int DecayingUtils::getDecayedProbability(const int rawProbability) {
+    return rawProbability;
+}
+
+} // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/decaying_utils.h b/native/jni/src/suggest/policyimpl/dictionary/utils/decaying_utils.h
new file mode 100644
index 0000000..1ca0391
--- /dev/null
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/decaying_utils.h
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2013, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef LATINIME_DECAYING_UTILS_H
+#define LATINIME_DECAYING_UTILS_H
+
+#include "defines.h"
+
+namespace latinime {
+
+// TODO: Check the elapsed time and decrease the probability depending on the time. Time field is
+// required to introduced to each terminal PtNode and bigram entry.
+// TODO: Quit using bigram probability to indicate the delta.
+// TODO: Quit using bigram probability delta.
+class DecayingUtils {
+ public:
+    static const int MAX_UNIGRAM_COUNT;
+    static const int MAX_UNIGRAM_COUNT_AFTER_GC;
+    static const int MAX_BIGRAM_COUNT;
+    static const int MAX_BIGRAM_COUNT_AFTER_GC;
+
+    static int getProbability(const int encodedUnigramProbability,
+            const int encodedBigramProbabilityDelta);
+
+    static int getUpdatedUnigramProbability(const int originalEncodedProbability,
+            const int newProbability);
+
+    static int getUpdatedBigramProbabilityDelta(const int originalEncodedProbabilityDelta,
+            const int newProbability);
+
+    static int isValidUnigram(const int encodedUnigramProbability);
+
+    static int isValidBigram(const int encodedProbabilityDelta);
+
+    static int getUnigramProbabilityToSave(const int encodedProbability);
+
+    static int getBigramProbabilityDeltaToSave(const int encodedProbabilityDelta);
+
+ private:
+    DISALLOW_IMPLICIT_CONSTRUCTORS(DecayingUtils);
+
+    static const int MAX_COMPUTED_PROBABILITY;
+    static const int MAX_UNIGRAM_PROBABILITY;
+    static const int MIN_VALID_UNIGRAM_PROBABILITY;
+    static const int UNIGRAM_PROBABILITY_STEP;
+    static const int MAX_BIGRAM_PROBABILITY_DELTA;
+    static const int MIN_VALID_BIGRAM_PROBABILITY_DELTA;
+    static const int BIGRAM_PROBABILITY_DELTA_STEP;
+
+    static int decodeUnigramProbability(const int encodedProbability);
+
+    static int decodeBigramProbabilityDelta(const int encodedProbability);
+
+    static int getDecayedProbability(const int rawProbability);
+};
+} // namespace latinime
+#endif /* LATINIME_DECAYING_UTILS_H */
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.cpp
index 4fae919..f22e94c 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/dict_file_writing_utils.cpp
@@ -96,7 +96,7 @@
         fclose(file);
         return false;
     }
-    const int additionalBufSize = buffer->getTailPosition() - buffer->getOriginalBufferSize();
+    const int additionalBufSize = buffer->getUsedAdditionalBufferSize();
     if (additionalBufSize > 0 && fwrite(buffer->getBuffer(true /* usesAdditionalBuffer */),
             additionalBufSize, 1, file) < 1) {
         fclose(file);
diff --git a/native/jni/src/suggest/policyimpl/typing/typing_weighting.cpp b/native/jni/src/suggest/policyimpl/typing/typing_weighting.cpp
index 408b12a..5b6b5e8 100644
--- a/native/jni/src/suggest/policyimpl/typing/typing_weighting.cpp
+++ b/native/jni/src/suggest/policyimpl/typing/typing_weighting.cpp
@@ -47,7 +47,7 @@
         case CT_TERMINAL_INSERTION:
         case CT_TRANSPOSITION:
             return ET_EDIT_CORRECTION;
-        case CT_NEW_WORD_SPACE_OMITTION:
+        case CT_NEW_WORD_SPACE_OMISSION:
         case CT_NEW_WORD_SPACE_SUBSTITUTION:
             return ET_NEW_WORD;
         case CT_TERMINAL:
diff --git a/tests/src/com/android/inputmethod/latin/BinaryDictionaryDecayingTests.java b/tests/src/com/android/inputmethod/latin/BinaryDictionaryDecayingTests.java
new file mode 100644
index 0000000..cf85d97
--- /dev/null
+++ b/tests/src/com/android/inputmethod/latin/BinaryDictionaryDecayingTests.java
@@ -0,0 +1,171 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.inputmethod.latin;
+
+import android.test.AndroidTestCase;
+import android.test.suitebuilder.annotation.LargeTest;
+
+import com.android.inputmethod.latin.makedict.FormatSpec;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Locale;
+import java.util.Map;
+
+@LargeTest
+public class BinaryDictionaryDecayingTests extends AndroidTestCase {
+    private static final String TEST_DICT_FILE_EXTENSION = ".testDict";
+    private static final String TEST_LOCALE = "test";
+
+    private static final int DUMMY_PROBABILITY = 0;
+
+    @Override
+    protected void setUp() throws Exception {
+        super.setUp();
+    }
+
+    @Override
+    protected void tearDown() throws Exception {
+        super.tearDown();
+    }
+
+    private void forcePassingShortTime(final BinaryDictionary binaryDictionary) {
+        binaryDictionary.flushWithGC();
+    }
+
+    private void forcePassingLongTime(final BinaryDictionary binaryDictionary) {
+        // Currently, probabilities are decayed when GC is run. All entries that have never been
+        // typed in 32 GCs are removed.
+        final int count = 32;
+        for (int i = 0; i < count; i++) {
+            binaryDictionary.flushWithGC();
+        }
+    }
+
+    private File createEmptyDictionaryAndGetFile(final String filename) throws IOException {
+        final File file = File.createTempFile(filename, TEST_DICT_FILE_EXTENSION,
+                getContext().getCacheDir());
+        Map<String, String> attributeMap = new HashMap<String, String>();
+        attributeMap.put(FormatSpec.FileHeader.SUPPORTS_DYNAMIC_UPDATE_ATTRIBUTE,
+                FormatSpec.FileHeader.ATTRIBUTE_VALUE_TRUE);
+        attributeMap.put(FormatSpec.FileHeader.USES_FORGETTING_CURVE_ATTRIBUTE,
+                FormatSpec.FileHeader.ATTRIBUTE_VALUE_TRUE);
+        if (BinaryDictionary.createEmptyDictFile(file.getAbsolutePath(),
+                3 /* dictVersion */, attributeMap)) {
+            return file;
+        } else {
+            throw new IOException("Empty dictionary cannot be created.");
+        }
+    }
+
+    public void testAddValidAndInvalidWords() {
+        File dictFile = null;
+        try {
+            dictFile = createEmptyDictionaryAndGetFile("TestBinaryDictionary");
+        } catch (IOException e) {
+            fail("IOException while writing an initial dictionary : " + e);
+        }
+        BinaryDictionary binaryDictionary = new BinaryDictionary(dictFile.getAbsolutePath(),
+                0 /* offset */, dictFile.length(), true /* useFullEditDistance */,
+                Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+
+        binaryDictionary.addUnigramWord("a", Dictionary.NOT_A_PROBABILITY);
+        assertFalse(binaryDictionary.isValidWord("a"));
+        binaryDictionary.addUnigramWord("a", Dictionary.NOT_A_PROBABILITY);
+        assertFalse(binaryDictionary.isValidWord("a"));
+        binaryDictionary.addUnigramWord("a", Dictionary.NOT_A_PROBABILITY);
+        assertFalse(binaryDictionary.isValidWord("a"));
+        binaryDictionary.addUnigramWord("a", Dictionary.NOT_A_PROBABILITY);
+        assertTrue(binaryDictionary.isValidWord("a"));
+
+        binaryDictionary.addUnigramWord("b", DUMMY_PROBABILITY);
+        assertTrue(binaryDictionary.isValidWord("b"));
+
+        final int unigramProbability = binaryDictionary.getFrequency("a");
+        binaryDictionary.addBigramWords("a", "b", Dictionary.NOT_A_PROBABILITY);
+        assertFalse(binaryDictionary.isValidBigram("a", "b"));
+        binaryDictionary.addBigramWords("a", "b", Dictionary.NOT_A_PROBABILITY);
+        assertFalse(binaryDictionary.isValidBigram("a", "b"));
+        binaryDictionary.addBigramWords("a", "b", Dictionary.NOT_A_PROBABILITY);
+        assertFalse(binaryDictionary.isValidBigram("a", "b"));
+        binaryDictionary.addBigramWords("a", "b", Dictionary.NOT_A_PROBABILITY);
+        assertTrue(binaryDictionary.isValidBigram("a", "b"));
+
+        binaryDictionary.addUnigramWord("c", DUMMY_PROBABILITY);
+        binaryDictionary.addBigramWords("a", "c", DUMMY_PROBABILITY);
+        assertTrue(binaryDictionary.isValidBigram("a", "c"));
+
+        binaryDictionary.close();
+        dictFile.delete();
+    }
+
+    // TODO: Add large tests.
+    public void testDecayingProbability() {
+        File dictFile = null;
+        try {
+            dictFile = createEmptyDictionaryAndGetFile("TestBinaryDictionary");
+        } catch (IOException e) {
+            fail("IOException while writing an initial dictionary : " + e);
+        }
+        BinaryDictionary binaryDictionary = new BinaryDictionary(dictFile.getAbsolutePath(),
+                0 /* offset */, dictFile.length(), true /* useFullEditDistance */,
+                Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        assertTrue(binaryDictionary.isValidWord("a"));
+        forcePassingShortTime(binaryDictionary);
+        assertFalse(binaryDictionary.isValidWord("a"));
+
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        forcePassingShortTime(binaryDictionary);
+        assertTrue(binaryDictionary.isValidWord("a"));
+        forcePassingLongTime(binaryDictionary);
+        assertFalse(binaryDictionary.isValidWord("a"));
+
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("b", DUMMY_PROBABILITY);
+        binaryDictionary.addBigramWords("a", "b", DUMMY_PROBABILITY);
+        assertTrue(binaryDictionary.isValidBigram("a", "b"));
+        forcePassingShortTime(binaryDictionary);
+        assertFalse(binaryDictionary.isValidBigram("a", "b"));
+
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("b", DUMMY_PROBABILITY);
+        binaryDictionary.addBigramWords("a", "b", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("b", DUMMY_PROBABILITY);
+        binaryDictionary.addBigramWords("a", "b", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("b", DUMMY_PROBABILITY);
+        binaryDictionary.addBigramWords("a", "b", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("a", DUMMY_PROBABILITY);
+        binaryDictionary.addUnigramWord("b", DUMMY_PROBABILITY);
+        binaryDictionary.addBigramWords("a", "b", DUMMY_PROBABILITY);
+        assertTrue(binaryDictionary.isValidBigram("a", "b"));
+        forcePassingShortTime(binaryDictionary);
+        assertTrue(binaryDictionary.isValidBigram("a", "b"));
+        forcePassingLongTime(binaryDictionary);
+        assertFalse(binaryDictionary.isValidBigram("a", "b"));
+
+        binaryDictionary.close();
+        dictFile.delete();
+    }
+}
diff --git a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
index 826c0f7..6a21522 100644
--- a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
@@ -606,7 +606,7 @@
             binaryDictionary = new BinaryDictionary(dictFile.getAbsolutePath(),
                     0 /* offset */, dictFile.length(), true /* useFullEditDistance */,
                     Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
-            while(!binaryDictionary.needsToRunGC()) {
+            while(!binaryDictionary.needsToRunGC(true /* mindsBlockByGC */)) {
                 final String word = CodePointUtils.generateWord(random, codePointSet);
                 words.add(word);
                 final int unigramProbability = random.nextInt(0xFF);
diff --git a/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
index 06c4271..ddc9546 100644
--- a/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
@@ -75,10 +75,10 @@
         return new ArrayList<String>(wordSet);
     }
 
-    private void addToDict(final UserHistoryPredictionDictionary dict, final List<String> words) {
+    private void addToDict(final UserHistoryDictionary dict, final List<String> words) {
         String prevWord = null;
         for (String word : words) {
-            dict.addToPersonalizationPredictionDictionary(prevWord, word, true);
+            dict.addToDictionary(prevWord, word, true);
             prevWord = word;
         }
     }
@@ -90,8 +90,8 @@
     private void addAndWriteRandomWords(final String testFilenameSuffix, final int numberOfWords,
             final Random random, final boolean checkContents) {
         final List<String> words = generateWords(numberOfWords, random);
-        final UserHistoryPredictionDictionary dict =
-                PersonalizationHelper.getUserHistoryPredictionDictionary(getContext(),
+        final UserHistoryDictionary dict =
+                PersonalizationHelper.getUserHistoryDictionary(getContext(),
                         testFilenameSuffix /* locale */, mPrefs);
         // Add random words to the user history dictionary.
         addToDict(dict, words);
@@ -122,8 +122,8 @@
                     true /* checksContents */);
         } finally {
             try {
-                final UserHistoryPredictionDictionary dict =
-                        PersonalizationHelper.getUserHistoryPredictionDictionary(getContext(),
+                final UserHistoryDictionary dict =
+                        PersonalizationHelper.getUserHistoryDictionary(getContext(),
                                 testFilenameSuffix, mPrefs);
                 Log.d(TAG, "waiting for writing ...");
                 dict.shutdownExecutorForTests();
@@ -134,7 +134,7 @@
                 Log.d(TAG, "InterruptedException: " + e);
             }
 
-            final String fileName = UserHistoryPredictionDictionary.NAME + "." + testFilenameSuffix
+            final String fileName = UserHistoryDictionary.NAME + "." + testFilenameSuffix
                     + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
             dictFile = new File(getContext().getFilesDir(), fileName);
 
@@ -159,7 +159,7 @@
             // Create filename suffixes for this test.
             for (int i = 0; i < numberOfLanguages; i++) {
                 testFilenameSuffixes[i] = "testSwitchingLanguages" + i;
-                final String fileName = UserHistoryPredictionDictionary.NAME + "." +
+                final String fileName = UserHistoryDictionary.NAME + "." +
                         testFilenameSuffixes[i] + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
                 dictFiles[i] = new File(getContext().getFilesDir(), fileName);
             }
@@ -181,8 +181,8 @@
             try {
                 Log.d(TAG, "waiting for writing ...");
                 for (int i = 0; i < numberOfLanguages; i++) {
-                    final UserHistoryPredictionDictionary dict =
-                            PersonalizationHelper.getUserHistoryPredictionDictionary(getContext(),
+                    final UserHistoryDictionary dict =
+                            PersonalizationHelper.getUserHistoryDictionary(getContext(),
                                     testFilenameSuffixes[i], mPrefs);
                     dict.shutdownExecutorForTests();
                     while (!dict.isTerminatedForTests()) {
@@ -210,8 +210,8 @@
                         10000 : 1000;
         final Random random = new Random(123456);
 
-        UserHistoryPredictionDictionary dict =
-                PersonalizationHelper.getUserHistoryPredictionDictionary(getContext(),
+        UserHistoryDictionary dict =
+                PersonalizationHelper.getUserHistoryDictionary(getContext(),
                         testFilenameSuffix, mPrefs);
         try {
             addAndWriteRandomWords(testFilenameSuffix, numberOfWords, random,
@@ -227,7 +227,7 @@
             } catch (InterruptedException e) {
                 Log.d(TAG, "InterruptedException: ", e);
             }
-            final String fileName = UserHistoryPredictionDictionary.NAME + "." + testFilenameSuffix
+            final String fileName = UserHistoryDictionary.NAME + "." + testFilenameSuffix
                     + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
             dictFile = new File(getContext().getFilesDir(), fileName);
             if (dictFile != null) {
diff --git a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/BinaryDictOffdeviceUtils.java b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/BinaryDictOffdeviceUtils.java
index 6c4cbcf..bd06e9f 100644
--- a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/BinaryDictOffdeviceUtils.java
+++ b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/BinaryDictOffdeviceUtils.java
@@ -80,17 +80,17 @@
     }
 
     /**
-     * Returns a decrypted/uncompressed binary dictionary.
+     * Returns a decrypted/uncompressed dictionary.
      *
-     * This will decrypt/uncompress any number of times as necessary until it finds the binary
+     * This will decrypt/uncompress any number of times as necessary until it finds the
      * dictionary signature, and copy the decoded file to a temporary place.
-     * If this is not a binary dictionary, the method returns null.
+     * If this is not a dictionary, the method returns null.
      */
-    public static DecoderChainSpec getRawBinaryDictionaryOrNull(final File src) {
-        return getRawBinaryDictionaryOrNullInternal(new DecoderChainSpec(), src, 0);
+    public static DecoderChainSpec getRawDictionaryOrNull(final File src) {
+        return getRawDictionaryOrNullInternal(new DecoderChainSpec(), src, 0);
     }
 
-    private static DecoderChainSpec getRawBinaryDictionaryOrNullInternal(
+    private static DecoderChainSpec getRawDictionaryOrNullInternal(
             final DecoderChainSpec spec, final File src, final int depth) {
         // Unfortunately the decoding scheme we use can consider any data to be encrypted
         // and will product some output, meaning it's not possible to reliably detect encrypted
@@ -98,7 +98,8 @@
         // over and over, ending in a stack overflow. Hence we limit the depth at which we try
         // decoding the file.
         if (depth > MAX_DECODE_DEPTH) return null;
-        if (BinaryDictDecoderUtils.isBinaryDictionary(src)) {
+        if (BinaryDictDecoderUtils.isBinaryDictionary(src)
+                || CombinedInputOutput.isCombinedDictionary(src.getAbsolutePath())) {
             spec.mFile = src;
             return spec;
         }
@@ -106,7 +107,7 @@
         final File uncompressedFile = tryGetUncompressedFile(src);
         if (null != uncompressedFile) {
             final DecoderChainSpec newSpec =
-                    getRawBinaryDictionaryOrNullInternal(spec, uncompressedFile, depth + 1);
+                    getRawDictionaryOrNullInternal(spec, uncompressedFile, depth + 1);
             if (null == newSpec) return null;
             return newSpec.addStep(COMPRESSION);
         }
@@ -114,7 +115,7 @@
         final File decryptedFile = tryGetDecryptedFile(src);
         if (null != decryptedFile) {
             final DecoderChainSpec newSpec =
-                    getRawBinaryDictionaryOrNullInternal(spec, decryptedFile, depth + 1);
+                    getRawDictionaryOrNullInternal(spec, decryptedFile, depth + 1);
             if (null == newSpec) return null;
             return newSpec.addStep(ENCRYPTION);
         }
@@ -175,15 +176,16 @@
                 return XmlDictInputOutput.readDictionaryXml(
                         new BufferedInputStream(new FileInputStream(file)),
                         null /* shortcuts */, null /* bigrams */);
-            } else if (CombinedInputOutput.isCombinedDictionary(filename)) {
-                if (report) System.out.println("Format : Combined format");
-                return CombinedInputOutput.readDictionaryCombined(
-                        new BufferedInputStream(new FileInputStream(file)));
             } else {
-                final DecoderChainSpec decodedSpec = getRawBinaryDictionaryOrNull(file);
+                final DecoderChainSpec decodedSpec = getRawDictionaryOrNull(file);
                 if (null == decodedSpec) {
                     crash(filename, new RuntimeException(
                             filename + " does not seem to be a dictionary file"));
+                } else if (CombinedInputOutput.isCombinedDictionary(
+                        decodedSpec.mFile.getAbsolutePath())){
+                    if (report) System.out.println("Format : Combined format");
+                    return CombinedInputOutput.readDictionaryCombined(
+                            new BufferedInputStream(new FileInputStream(decodedSpec.mFile)));
                 } else {
                     final DictDecoder dictDecoder = FormatSpec.getDictDecoder(decodedSpec.mFile,
                             DictDecoder.USE_BYTEARRAY);
diff --git a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Package.java b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Package.java
index 9274dcd..dff3387 100644
--- a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Package.java
+++ b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Package.java
@@ -79,7 +79,7 @@
                 throw new RuntimeException("Too many/too few arguments for command " + COMMAND);
             }
             final BinaryDictOffdeviceUtils.DecoderChainSpec decodedSpec =
-                    BinaryDictOffdeviceUtils.getRawBinaryDictionaryOrNull(new File(mArgs[0]));
+                    BinaryDictOffdeviceUtils.getRawDictionaryOrNull(new File(mArgs[0]));
             if (null == decodedSpec) {
                 System.out.println(mArgs[0] + " does not seem to be a dictionary");
                 return;
diff --git a/tools/dicttool/tests/com/android/inputmethod/latin/dicttool/BinaryDictOffdeviceUtilsTests.java b/tools/dicttool/tests/com/android/inputmethod/latin/dicttool/BinaryDictOffdeviceUtilsTests.java
index 1eff497..1baeb7a 100644
--- a/tools/dicttool/tests/com/android/inputmethod/latin/dicttool/BinaryDictOffdeviceUtilsTests.java
+++ b/tools/dicttool/tests/com/android/inputmethod/latin/dicttool/BinaryDictOffdeviceUtilsTests.java
@@ -64,7 +64,7 @@
 
         // Test for an actually compressed dictionary and its contents
         final BinaryDictOffdeviceUtils.DecoderChainSpec decodeSpec =
-                BinaryDictOffdeviceUtils.getRawBinaryDictionaryOrNull(dst);
+                BinaryDictOffdeviceUtils.getRawDictionaryOrNull(dst);
         for (final String step : decodeSpec.mDecoderSpec) {
             assertEquals("Wrong decode spec", BinaryDictOffdeviceUtils.COMPRESSION, step);
         }
@@ -90,7 +90,7 @@
 
         // Test that a random data file actually fails
         assertNull("Wrongly identified data file",
-                BinaryDictOffdeviceUtils.getRawBinaryDictionaryOrNull(dst));
+                BinaryDictOffdeviceUtils.getRawDictionaryOrNull(dst));
 
         final File gzDst = File.createTempFile("testGetRawDict", ".tmp");
         gzDst.deleteOnExit();
@@ -103,6 +103,6 @@
 
         // Test that a compressed random data file actually fails
         assertNull("Wrongly identified data file",
-                BinaryDictOffdeviceUtils.getRawBinaryDictionaryOrNull(gzDst));
+                BinaryDictOffdeviceUtils.getRawDictionaryOrNull(gzDst));
     }
 }