diff --git a/ui/build/Android.bp b/ui/build/Android.bp
index 7a8fca9..b79754c 100644
--- a/ui/build/Android.bp
+++ b/ui/build/Android.bp
@@ -50,6 +50,7 @@
         "cleanbuild.go",
         "config.go",
         "context.go",
+        "staging_snapshot.go",
         "dumpvars.go",
         "environment.go",
         "exec.go",
@@ -70,10 +71,11 @@
         "cleanbuild_test.go",
         "config_test.go",
         "environment_test.go",
+        "proc_sync_test.go",
         "rbe_test.go",
+        "staging_snapshot_test.go",
         "upload_test.go",
         "util_test.go",
-        "proc_sync_test.go",
     ],
     darwin: {
         srcs: [
diff --git a/ui/build/build.go b/ui/build/build.go
index d49a754..edc595d 100644
--- a/ui/build/build.go
+++ b/ui/build/build.go
@@ -102,9 +102,9 @@
 	// Whether to include the kati-generated ninja file in the combined ninja.
 	RunKatiNinja = 1 << iota
 	// Whether to run ninja on the combined ninja.
-	RunNinja      = 1 << iota
-	RunBuildTests = 1 << iota
-	RunAll        = RunProductConfig | RunSoong | RunKati | RunKatiNinja | RunNinja
+	RunNinja       = 1 << iota
+	RunDistActions = 1 << iota
+	RunBuildTests  = 1 << iota
 )
 
 // checkBazelMode fails the build if there are conflicting arguments for which bazel
@@ -322,34 +322,42 @@
 
 		runNinjaForBuild(ctx, config)
 	}
+
+	if what&RunDistActions != 0 {
+		runDistActions(ctx, config)
+	}
 }
 
 func evaluateWhatToRun(config Config, verboseln func(v ...interface{})) int {
 	//evaluate what to run
-	what := RunAll
+	what := 0
 	if config.Checkbuild() {
 		what |= RunBuildTests
 	}
-	if config.SkipConfig() {
+	if !config.SkipConfig() {
+		what |= RunProductConfig
+	} else {
 		verboseln("Skipping Config as requested")
-		what = what &^ RunProductConfig
 	}
-	if config.SkipKati() {
-		verboseln("Skipping Kati as requested")
-		what = what &^ RunKati
-	}
-	if config.SkipKatiNinja() {
-		verboseln("Skipping use of Kati ninja as requested")
-		what = what &^ RunKatiNinja
-	}
-	if config.SkipSoong() {
+	if !config.SkipSoong() {
+		what |= RunSoong
+	} else {
 		verboseln("Skipping use of Soong as requested")
-		what = what &^ RunSoong
 	}
-
-	if config.SkipNinja() {
+	if !config.SkipKati() {
+		what |= RunKati
+	} else {
+		verboseln("Skipping Kati as requested")
+	}
+	if !config.SkipKatiNinja() {
+		what |= RunKatiNinja
+	} else {
+		verboseln("Skipping use of Kati ninja as requested")
+	}
+	if !config.SkipNinja() {
+		what |= RunNinja
+	} else {
 		verboseln("Skipping Ninja as requested")
-		what = what &^ RunNinja
 	}
 
 	if !config.SoongBuildInvocationNeeded() {
@@ -361,6 +369,11 @@
 		what = what &^ RunNinja
 		what = what &^ RunKati
 	}
+
+	if config.Dist() {
+		what |= RunDistActions
+	}
+
 	return what
 }
 
@@ -419,3 +432,9 @@
 		}
 	}()
 }
+
+// Actions to run on every build where 'dist' is in the actions.
+// Be careful, anything added here slows down EVERY CI build
+func runDistActions(ctx Context, config Config) {
+	runStagingSnapshot(ctx, config)
+}
diff --git a/ui/build/staging_snapshot.go b/ui/build/staging_snapshot.go
new file mode 100644
index 0000000..377aa64
--- /dev/null
+++ b/ui/build/staging_snapshot.go
@@ -0,0 +1,246 @@
+// Copyright 2023 Google Inc. All rights reserved.
+//
+// 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 build
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"encoding/json"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	"android/soong/shared"
+	"android/soong/ui/metrics"
+)
+
+// Metadata about a staged file
+type fileEntry struct {
+	Name string      `json:"name"`
+	Mode fs.FileMode `json:"mode"`
+	Size int64       `json:"size"`
+	Sha1 string      `json:"sha1"`
+}
+
+func fileEntryEqual(a fileEntry, b fileEntry) bool {
+	return a.Name == b.Name && a.Mode == b.Mode && a.Size == b.Size && a.Sha1 == b.Sha1
+}
+
+func sha1_hash(filename string) (string, error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	h := sha1.New()
+	if _, err := io.Copy(h, f); err != nil {
+		return "", err
+	}
+
+	return hex.EncodeToString(h.Sum(nil)), nil
+}
+
+// Subdirs of PRODUCT_OUT to scan
+var stagingSubdirs = []string{
+	"apex",
+	"cache",
+	"coverage",
+	"data",
+	"debug_ramdisk",
+	"fake_packages",
+	"installer",
+	"oem",
+	"product",
+	"ramdisk",
+	"recovery",
+	"root",
+	"sysloader",
+	"system",
+	"system_dlkm",
+	"system_ext",
+	"system_other",
+	"testcases",
+	"test_harness_ramdisk",
+	"vendor",
+	"vendor_debug_ramdisk",
+	"vendor_kernel_ramdisk",
+	"vendor_ramdisk",
+}
+
+// Return an array of stagedFileEntrys, one for each file in the staging directories inside
+// productOut
+func takeStagingSnapshot(ctx Context, productOut string, subdirs []string) ([]fileEntry, error) {
+	var outer_err error
+	if !strings.HasSuffix(productOut, "/") {
+		productOut += "/"
+	}
+	result := []fileEntry{}
+	for _, subdir := range subdirs {
+		filepath.WalkDir(productOut+subdir,
+			func(filename string, dirent fs.DirEntry, err error) error {
+				// Ignore errors. The most common one is that one of the subdirectories
+				// hasn't been built, in which case we just report it as empty.
+				if err != nil {
+					ctx.Verbosef("scanModifiedStagingOutputs error: %s", err)
+					return nil
+				}
+				if dirent.Type().IsRegular() {
+					fileInfo, _ := dirent.Info()
+					relative := strings.TrimPrefix(filename, productOut)
+					sha, err := sha1_hash(filename)
+					if err != nil {
+						outer_err = err
+					}
+					result = append(result, fileEntry{
+						Name: relative,
+						Mode: fileInfo.Mode(),
+						Size: fileInfo.Size(),
+						Sha1: sha,
+					})
+				}
+				return nil
+			})
+	}
+
+	sort.Slice(result, func(l, r int) bool { return result[l].Name < result[r].Name })
+
+	return result, outer_err
+}
+
+// Read json into an array of fileEntry. On error return empty array.
+func readJson(filename string) ([]fileEntry, error) {
+	buf, err := os.ReadFile(filename)
+	if err != nil {
+		// Not an error, just missing, which is empty.
+		return []fileEntry{}, nil
+	}
+
+	var result []fileEntry
+	err = json.Unmarshal(buf, &result)
+	if err != nil {
+		// Bad formatting. This is an error
+		return []fileEntry{}, err
+	}
+
+	return result, nil
+}
+
+// Write obj to filename.
+func writeJson(filename string, obj interface{}) error {
+	buf, err := json.MarshalIndent(obj, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	return os.WriteFile(filename, buf, 0660)
+}
+
+type snapshotDiff struct {
+	Added   []string `json:"added"`
+	Changed []string `json:"changed"`
+	Removed []string `json:"removed"`
+}
+
+// Diff the two snapshots, returning a snapshotDiff.
+func diffSnapshots(previous []fileEntry, current []fileEntry) snapshotDiff {
+	result := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{},
+		Removed: []string{},
+	}
+
+	found := make(map[string]bool)
+
+	prev := make(map[string]fileEntry)
+	for _, pre := range previous {
+		prev[pre.Name] = pre
+	}
+
+	for _, cur := range current {
+		pre, ok := prev[cur.Name]
+		found[cur.Name] = true
+		// Added
+		if !ok {
+			result.Added = append(result.Added, cur.Name)
+			continue
+		}
+		// Changed
+		if !fileEntryEqual(pre, cur) {
+			result.Changed = append(result.Changed, cur.Name)
+		}
+	}
+
+	// Removed
+	for _, pre := range previous {
+		if !found[pre.Name] {
+			result.Removed = append(result.Removed, pre.Name)
+		}
+	}
+
+	// Sort the results
+	sort.Strings(result.Added)
+	sort.Strings(result.Changed)
+	sort.Strings(result.Removed)
+
+	return result
+}
+
+// Write a json files to dist:
+//   - A list of which files have changed in this build.
+//
+// And record in out/soong:
+//   - A list of all files in the staging directories, including their hashes.
+func runStagingSnapshot(ctx Context, config Config) {
+	ctx.BeginTrace(metrics.RunSoong, "runStagingSnapshot")
+	defer ctx.EndTrace()
+
+	snapshotFilename := shared.JoinPath(config.SoongOutDir(), "staged_files.json")
+
+	// Read the existing snapshot file. If it doesn't exist, this is a full
+	// build, so all files will be treated as new.
+	previous, err := readJson(snapshotFilename)
+	if err != nil {
+		ctx.Fatal(err)
+		return
+	}
+
+	// Take a snapshot of the current out directory
+	current, err := takeStagingSnapshot(ctx, config.ProductOut(), stagingSubdirs)
+	if err != nil {
+		ctx.Fatal(err)
+		return
+	}
+
+	// Diff the snapshots
+	diff := diffSnapshots(previous, current)
+
+	// Write the diff (use RealDistDir, not one that might have been faked for bazel)
+	err = writeJson(shared.JoinPath(config.RealDistDir(), "modified_files.json"), diff)
+	if err != nil {
+		ctx.Fatal(err)
+		return
+	}
+
+	// Update the snapshot
+	err = writeJson(snapshotFilename, current)
+	if err != nil {
+		ctx.Fatal(err)
+		return
+	}
+}
diff --git a/ui/build/staging_snapshot_test.go b/ui/build/staging_snapshot_test.go
new file mode 100644
index 0000000..7ac5443
--- /dev/null
+++ b/ui/build/staging_snapshot_test.go
@@ -0,0 +1,188 @@
+// Copyright 2023 Google Inc. All rights reserved.
+//
+// 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 build
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+func assertDeepEqual(t *testing.T, expected interface{}, actual interface{}) {
+	if !reflect.DeepEqual(actual, expected) {
+		t.Fatalf("expected:\n  %#v\n actual:\n  %#v", expected, actual)
+	}
+}
+
+// Make a temp directory containing the supplied contents
+func makeTempDir(files []string, directories []string, symlinks []string) string {
+	temp, _ := os.MkdirTemp("", "soon_staging_snapshot_test_")
+
+	for _, file := range files {
+		os.MkdirAll(temp+"/"+filepath.Dir(file), 0700)
+		os.WriteFile(temp+"/"+file, []byte(file), 0600)
+	}
+
+	for _, dir := range directories {
+		os.MkdirAll(temp+"/"+dir, 0770)
+	}
+
+	for _, symlink := range symlinks {
+		os.MkdirAll(temp+"/"+filepath.Dir(symlink), 0770)
+		os.Symlink(temp, temp+"/"+symlink)
+	}
+
+	return temp
+}
+
+// If this is a clean build, we won't have any preexisting files, make sure we get back an empty
+// list and not errors.
+func TestEmptyOut(t *testing.T) {
+	ctx := testContext()
+
+	temp := makeTempDir(nil, nil, nil)
+	defer os.RemoveAll(temp)
+
+	actual, _ := takeStagingSnapshot(ctx, temp, []string{"a", "e", "g"})
+
+	expected := []fileEntry{}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure only the listed directories are picked up, and only regular files
+func TestNoExtraSubdirs(t *testing.T) {
+	ctx := testContext()
+
+	temp := makeTempDir([]string{"a/b", "a/c", "d", "e/f"}, []string{"g/h"}, []string{"e/symlink"})
+	defer os.RemoveAll(temp)
+
+	actual, _ := takeStagingSnapshot(ctx, temp, []string{"a", "e", "g"})
+
+	expected := []fileEntry{
+		{"a/b", 0600, 3, "3ec69c85a4ff96830024afeef2d4e512181c8f7b"},
+		{"a/c", 0600, 3, "592d70e4e03ee6f6780c71b0bf3b9608dbf1e201"},
+		{"e/f", 0600, 3, "9e164bef74aceede0974b857170100409efe67f1"},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles empty lists
+func TestDiffEmpty(t *testing.T) {
+	actual := diffSnapshots(nil, []fileEntry{})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles adding
+func TestDiffAdd(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{"b"},
+		Changed: []string{},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles changing mode
+func TestDiffChangeMode(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0600, 2, "5678"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{"b"},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles changing size
+func TestDiffChangeSize(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 3, "5678"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{"b"},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles changing contents
+func TestDiffChangeContents(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "aaaa"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{"b"},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles removing
+func TestDiffRemove(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{},
+		Removed: []string{"b"},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}