diff --git a/core/dex_preopt_config.mk b/core/dex_preopt_config.mk
index 51238a3..0c806c1 100644
--- a/core/dex_preopt_config.mk
+++ b/core/dex_preopt_config.mk
@@ -104,11 +104,11 @@
   $(call add_json_bool, DisableGenerateProfile,                  $(filter false,$(WITH_DEX_PREOPT_GENERATE_PROFILE)))
   $(call add_json_str,  ProfileDir,                              $(PRODUCT_DEX_PREOPT_PROFILE_DIR))
   $(call add_json_list, BootJars,                                $(PRODUCT_BOOT_JARS))
-  $(call add_json_list, UpdatableBootJars,                       $(PRODUCT_UPDATABLE_BOOT_JARS))
+  $(call add_json_list, ApexBootJars,                            $(PRODUCT_APEX_BOOT_JARS))
   $(call add_json_list, ArtApexJars,                             $(filter $(PRODUCT_BOOT_JARS),$(ART_APEX_JARS)))
   $(call add_json_list, SystemServerJars,                        $(PRODUCT_SYSTEM_SERVER_JARS))
   $(call add_json_list, SystemServerApps,                        $(PRODUCT_SYSTEM_SERVER_APPS))
-  $(call add_json_list, UpdatableSystemServerJars,               $(PRODUCT_UPDATABLE_SYSTEM_SERVER_JARS))
+  $(call add_json_list, ApexSystemServerJars,                    $(PRODUCT_APEX_SYSTEM_SERVER_JARS))
   $(call add_json_bool, BrokenSuboptimalOrderOfSystemServerJars, $(PRODUCT_BROKEN_SUBOPTIMAL_ORDER_OF_SYSTEM_SERVER_JARS))
   $(call add_json_list, SpeedApps,                               $(PRODUCT_DEXPREOPT_SPEED_APPS))
   $(call add_json_list, PreoptFlags,                             $(PRODUCT_DEX_PREOPT_DEFAULT_FLAGS))
diff --git a/core/dex_preopt_odex_install.mk b/core/dex_preopt_odex_install.mk
index a2837f3..1983022 100644
--- a/core/dex_preopt_odex_install.mk
+++ b/core/dex_preopt_odex_install.mk
@@ -61,7 +61,7 @@
 endif
 
 # Don't preopt system server jars that are updatable.
-ifneq (,$(filter %:$(LOCAL_MODULE), $(PRODUCT_UPDATABLE_SYSTEM_SERVER_JARS)))
+ifneq (,$(filter %:$(LOCAL_MODULE), $(PRODUCT_APEX_SYSTEM_SERVER_JARS)))
   LOCAL_DEX_PREOPT :=
 endif
 
diff --git a/core/product.mk b/core/product.mk
index 015fe44..eb99a9b 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -228,7 +228,7 @@
 _product_list_vars += PRODUCT_SYSTEM_SERVER_APPS
 _product_list_vars += PRODUCT_SYSTEM_SERVER_JARS
 # List of system_server jars delivered via apex. Format = <apex name>:<jar name>.
-_product_list_vars += PRODUCT_UPDATABLE_SYSTEM_SERVER_JARS
+_product_list_vars += PRODUCT_APEX_SYSTEM_SERVER_JARS
 # If true, then suboptimal order of system server jars does not cause an error.
 _product_single_value_vars += PRODUCT_BROKEN_SUBOPTIMAL_ORDER_OF_SYSTEM_SERVER_JARS
 
@@ -368,7 +368,7 @@
 
 # A list of <overridden-apex>:<override-apex> pairs that specifies APEX module
 # overrides to be applied to the APEX names in the boot jar variables
-# (PRODUCT_BOOT_JARS, PRODUCT_UPDATABLE_BOOT_JARS etc).
+# (PRODUCT_BOOT_JARS, PRODUCT_APEX_BOOT_JARS etc).
 _product_list_vars += PRODUCT_BOOT_JAR_MODULE_OVERRIDES
 
 # Controls for whether different partitions are built for the current product.
@@ -389,8 +389,9 @@
 _product_single_value_vars += PRODUCT_BUILD_VBMETA_IMAGE
 _product_single_value_vars += PRODUCT_BUILD_SUPER_EMPTY_IMAGE
 
-# List of boot jars delivered via apex
-_product_list_vars += PRODUCT_UPDATABLE_BOOT_JARS
+# List of boot jars delivered via updatable APEXes, following the same format as
+# PRODUCT_BOOT_JARS.
+_product_list_vars += PRODUCT_APEX_BOOT_JARS
 
 # If set, device uses virtual A/B.
 _product_single_value_vars += PRODUCT_VIRTUAL_AB_OTA
diff --git a/core/product_config.mk b/core/product_config.mk
index 5c85fb8..a9f3d34 100644
--- a/core/product_config.mk
+++ b/core/product_config.mk
@@ -249,6 +249,15 @@
 
 PRODUCT_BOOT_JARS := $(call qualify-platform-jars,$(PRODUCT_BOOT_JARS))
 
+# b/191127295: force core-icu4j onto boot image. It comes from a non-updatable APEX jar, but has
+# historically been part of the boot image; even though APEX jars are not meant to be part of the
+# boot image.
+# TODO(b/191686720): remove PRODUCT_APEX_BOOT_JARS to avoid a special handling of core-icu4j
+# in make rules.
+PRODUCT_APEX_BOOT_JARS := $(filter-out com.android.i18n:core-icu4j,$(PRODUCT_APEX_BOOT_JARS))
+# All APEX jars come after /system and /system_ext jars, so adding core-icu4j at the end of the list
+PRODUCT_BOOT_JARS += com.android.i18n:core-icu4j
+
 # Replaces references to overridden boot jar modules in a boot jars variable.
 # $(1): Name of a boot jars variable with <apex>:<jar> pairs.
 define replace-boot-jar-module-overrides
@@ -259,7 +268,7 @@
 endef
 
 $(call replace-boot-jar-module-overrides,PRODUCT_BOOT_JARS)
-$(call replace-boot-jar-module-overrides,PRODUCT_UPDATABLE_BOOT_JARS)
+$(call replace-boot-jar-module-overrides,PRODUCT_APEX_BOOT_JARS)
 $(call replace-boot-jar-module-overrides,ART_APEX_JARS)
 
 # The extra system server jars must be appended at the end after common system server jars.
@@ -303,10 +312,10 @@
   endif
 endif
 
-$(foreach pair,$(PRODUCT_UPDATABLE_BOOT_JARS), \
+$(foreach pair,$(PRODUCT_APEX_BOOT_JARS), \
   $(eval jar := $(call word-colon,2,$(pair))) \
   $(if $(findstring $(jar), $(PRODUCT_BOOT_JARS)), \
-    $(error A jar in PRODUCT_UPDATABLE_BOOT_JARS must not be in PRODUCT_BOOT_JARS, but $(jar) is)))
+    $(error A jar in PRODUCT_APEX_BOOT_JARS must not be in PRODUCT_BOOT_JARS, but $(jar) is)))
 
 ENFORCE_SYSTEM_CERTIFICATE := $(PRODUCT_ENFORCE_ARTIFACT_SYSTEM_CERTIFICATE_REQUIREMENT)
 ENFORCE_SYSTEM_CERTIFICATE_ALLOW_LIST := $(PRODUCT_ARTIFACT_SYSTEM_CERTIFICATE_REQUIREMENT_ALLOW_LIST)
diff --git a/core/soong_config.mk b/core/soong_config.mk
index ec67560..e0fd9be 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -27,6 +27,7 @@
 $(call add_json_val,  Platform_sdk_version,              $(PLATFORM_SDK_VERSION))
 $(call add_json_str,  Platform_sdk_codename,             $(PLATFORM_VERSION_CODENAME))
 $(call add_json_bool, Platform_sdk_final,                $(filter REL,$(PLATFORM_VERSION_CODENAME)))
+$(call add_json_val,  Platform_sdk_extension_version,    $(PLATFORM_SDK_EXTENSION_VERSION))
 $(call add_json_csv,  Platform_version_active_codenames, $(PLATFORM_VERSION_ALL_CODENAMES))
 $(call add_json_str,  Platform_security_patch,           $(PLATFORM_SECURITY_PATCH))
 $(call add_json_str,  Platform_preview_sdk_version,      $(PLATFORM_PREVIEW_SDK_VERSION))
@@ -141,7 +142,7 @@
 $(call add_json_list, ModulesLoadedByPrivilegedModules,  $(PRODUCT_LOADED_BY_PRIVILEGED_MODULES))
 
 $(call add_json_list, BootJars,                          $(PRODUCT_BOOT_JARS))
-$(call add_json_list, UpdatableBootJars,                 $(PRODUCT_UPDATABLE_BOOT_JARS))
+$(call add_json_list, ApexBootJars,                      $(PRODUCT_APEX_BOOT_JARS))
 
 $(call add_json_bool, VndkUseCoreVariant,                $(TARGET_VNDK_USE_CORE_VARIANT))
 $(call add_json_bool, VndkSnapshotBuildArtifacts,        $(VNDK_SNAPSHOT_BUILD_ARTIFACTS))
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 4c83227..dbc32e1 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -155,6 +155,12 @@
 endif
 .KATI_READONLY := PLATFORM_SDK_VERSION
 
+# This is the sdk extension version of this tree.
+PLATFORM_SDK_EXTENSION_VERSION :=$= 1
+
+# This is the sdk extension version that PLATFORM_SDK_VERSION ships with.
+PLATFORM_BASE_SDK_EXTENSION_VERSION :=$= 0
+
 ifeq (REL,$(PLATFORM_VERSION_CODENAME))
   PLATFORM_PREVIEW_SDK_VERSION := 0
 else
diff --git a/target/product/default_art_config.mk b/target/product/default_art_config.mk
index 0fa9058..1a32fd9 100644
--- a/target/product/default_art_config.mk
+++ b/target/product/default_art_config.mk
@@ -27,7 +27,7 @@
 #
 # ART APEX jars (1) are defined in ART_APEX_JARS. System, system_ext, and non updatable boot jars
 # are defined below in PRODUCT_BOOT_JARS. All updatable APEX boot jars are part of
-# PRODUCT_UPDATABLE_BOOT_JARS.
+# PRODUCT_APEX_BOOT_JARS.
 #
 # The actual runtime ordering matching above is determined by derive_classpath service at runtime.
 # See packages/modules/SdkExtensions/README.md for more details.
@@ -45,14 +45,12 @@
     voip-common \
     ims-common
 
-# Non-updatable APEX jars. Keep the list sorted.
-PRODUCT_BOOT_JARS += \
-    com.android.i18n:core-icu4j
-
-# Updatable APEX boot jars. Keep the list sorted by module names and then library names.
-PRODUCT_UPDATABLE_BOOT_JARS := \
+# APEX boot jars. Keep the list sorted by module names and then library names.
+# Note: core-icu4j is moved back to PRODUCT_BOOT_JARS in product_config.mk at a later stage.
+PRODUCT_APEX_BOOT_JARS := \
     com.android.appsearch:framework-appsearch \
     com.android.conscrypt:conscrypt \
+    com.android.i18n:core-icu4j \
     com.android.ipsec:android.net.ipsec.ike \
     com.android.media:updatable-media \
     com.android.mediaprovider:framework-mediaprovider \
@@ -65,8 +63,8 @@
     com.android.tethering:framework-tethering \
     com.android.wifi:framework-wifi
 
-# Updatable APEX system server jars. Keep the list sorted by module names and then library names.
-PRODUCT_UPDATABLE_SYSTEM_SERVER_JARS := \
+# APEX system server jars. Keep the list sorted by module names and then library names.
+PRODUCT_APEX_SYSTEM_SERVER_JARS := \
     com.android.appsearch:service-appsearch \
     com.android.media:service-media-s \
     com.android.permission:service-permission \