diff --git a/WordPress/src/main/java/org/wordpress/android/ui/posts/EditPostActivity.java b/WordPress/src/main/java/org/wordpress/android/ui/posts/EditPostActivity.java
index baaa9de7e0bc..2c4b75d19693 100644
--- a/WordPress/src/main/java/org/wordpress/android/ui/posts/EditPostActivity.java
+++ b/WordPress/src/main/java/org/wordpress/android/ui/posts/EditPostActivity.java
@@ -3301,7 +3301,9 @@ private void onEditorFinalTouchesBeforeShowing() {
                 ((GutenbergEditorFragment) mEditorFragment).resetUploadingMediaToFailed(mediaIds);
             }
         } else if (mShowAztecEditor && mEditorFragment instanceof AztecEditorFragment) {
-            mPostEditorAnalyticsSession.start(null, canViewEditorOnboarding());
+            EditorTheme editorTheme = mEditorThemeStore.getEditorThemeForSite(mSite);
+            Boolean supportsGalleryWithImageBlocks = editorTheme.getThemeSupport().getGalleryWithImageBlocks();
+            mPostEditorAnalyticsSession.start(null, canViewEditorOnboarding(), supportsGalleryWithImageBlocks);
         }
     }
 
@@ -3314,7 +3316,15 @@ public void onEditorFragmentContentReady(
         // It assumes this is being called when the editor has finished loading
         // If you need to refactor this, please ensure that the startup_time_ms property
         // is still reflecting the actual startup time of the editor
-        mPostEditorAnalyticsSession.start(unsupportedBlocksList, canViewEditorOnboarding());
+        EditorTheme editorTheme = mEditorThemeStore.getEditorThemeForSite(mSite);
+        Boolean supportsGalleryWithImageBlocks = null;
+        if (editorTheme != null) {
+            // Note that if the editor theme has not been initialized (usually on the first app run) the
+            // `unstableGalleryWithImageBlocks` analytics property will not be reported
+            supportsGalleryWithImageBlocks = editorTheme.getThemeSupport().getGalleryWithImageBlocks();
+        }
+        mPostEditorAnalyticsSession
+                .start(unsupportedBlocksList, canViewEditorOnboarding(), supportsGalleryWithImageBlocks);
         presentNewPageNoticeIfNeeded();
 
         // don't start listening for Story events just now if we're waiting for a block to be replaced,
diff --git a/WordPress/src/main/java/org/wordpress/android/ui/posts/PostEditorAnalyticsSession.java b/WordPress/src/main/java/org/wordpress/android/ui/posts/PostEditorAnalyticsSession.java
index 3d3536b48648..4417ad6fa701 100644
--- a/WordPress/src/main/java/org/wordpress/android/ui/posts/PostEditorAnalyticsSession.java
+++ b/WordPress/src/main/java/org/wordpress/android/ui/posts/PostEditorAnalyticsSession.java
@@ -24,6 +24,7 @@ public class PostEditorAnalyticsSession implements Serializable {
     private static final String KEY_HAS_UNSUPPORTED_BLOCKS = "has_unsupported_blocks";
     private static final String KEY_UNSUPPORTED_BLOCKS = "unsupported_blocks";
     private static final String KEY_CAN_VIEW_EDITOR_ONBOARDING = "can_view_editor_onboarding";
+    private static final String KEY_GALLERY_WITH_IMAGE_BLOCKS = "unstableGalleryWithImageBlocks";
     private static final String KEY_POST_TYPE = "post_type";
     private static final String KEY_OUTCOME = "outcome";
     private static final String KEY_SESSION_ID = "session_id";
@@ -97,7 +98,9 @@ public static PostEditorAnalyticsSession getNewPostEditorAnalyticsSession(
         return new PostEditorAnalyticsSession(editor, post, site, isNewPost);
     }
 
-    public void start(ArrayList<Object> unsupportedBlocksList, Boolean canViewEditorOnboarding) {
+    public void start(ArrayList<Object> unsupportedBlocksList,
+                      Boolean canViewEditorOnboarding,
+                      Boolean galleryWithImageBlocks) {
         if (!mStarted) {
             mHasUnsupportedBlocks = unsupportedBlocksList != null && unsupportedBlocksList.size() > 0;
             Map<String, Object> properties = getCommonProperties();
@@ -106,6 +109,9 @@ public void start(ArrayList<Object> unsupportedBlocksList, Boolean canViewEditor
             if (canViewEditorOnboarding != null) {
                 properties.put(KEY_CAN_VIEW_EDITOR_ONBOARDING, canViewEditorOnboarding);
             }
+            if (galleryWithImageBlocks != null) {
+                properties.put(KEY_GALLERY_WITH_IMAGE_BLOCKS, galleryWithImageBlocks);
+            }
             // Note that start time only counts when the analytics session was created and not when the editor
             // activity started. We are mostly interested in measuring the loading times for the block editor,
             // where the main bottleneck seems to be initializing React Native and doing the initial load of Gutenberg.
diff --git a/WordPress/src/main/java/org/wordpress/android/ui/stories/StoryComposerViewModel.kt b/WordPress/src/main/java/org/wordpress/android/ui/stories/StoryComposerViewModel.kt
index 04dbb2052bbd..e6a06aafff09 100644
--- a/WordPress/src/main/java/org/wordpress/android/ui/stories/StoryComposerViewModel.kt
+++ b/WordPress/src/main/java/org/wordpress/android/ui/stories/StoryComposerViewModel.kt
@@ -114,7 +114,7 @@ class StoryComposerViewModel @Inject constructor(
                 editPostRepository.getPost(),
                 site
         )
-        this.postEditorAnalyticsSession?.start(null, null)
+        this.postEditorAnalyticsSession?.start(null, null, null)
     }
 
     private fun createPostEditorAnalyticsSessionTracker(