diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index c7c7abb3a3b..45331fd2e37 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1062,6 +1062,12 @@ declare module 'vscode' {
 		 */
 		readonly inputBox: CommentInputBox | undefined;
 
+		/**
+		 * The active [comment thread](#CommentThread) or `undefined`. The `activeCommentThread` is the comment thread of
+		 * the comment thread widget that currently has focus. It's `undefined` when the focus is not in any comment thread widget.
+		 */
+		readonly activeCommentThread: CommentThread | undefined;
+
 		/**
 		 * Create a [CommentThread](#CommentThread). The comment thread will be displayed in visible text editors (if the resource matches)
 		 * and Comments Panel.
diff --git a/src/vs/workbench/api/browser/mainThreadComments.ts b/src/vs/workbench/api/browser/mainThreadComments.ts
index 7fb1f2c50b0..f7e791f868e 100644
--- a/src/vs/workbench/api/browser/mainThreadComments.ts
+++ b/src/vs/workbench/api/browser/mainThreadComments.ts
@@ -458,6 +458,7 @@ export class MainThreadComments extends Disposable implements MainThreadComments
 				this._proxy.$onCommentWidgetInputChange(controller.handle, this._input ? this._input.value : undefined);
 			}));
 
+			await this._proxy.$onActiveCommentThreadChange(controller.handle, controller.activeCommentThread.commentThreadHandle);
 			await this._proxy.$onCommentWidgetInputChange(controller.handle, this._input ? this._input.value : undefined);
 		}));
 	}
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index 0515075538c..bc847725bb6 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -1203,6 +1203,7 @@ export interface ExtHostCommentsShape {
 	$provideDocumentComments(handle: number, document: UriComponents): Promise<modes.CommentInfo | null>;
 	$createNewCommentThread(handle: number, document: UriComponents, range: IRange, text: string): Promise<modes.CommentThread | null>;
 	$onCommentWidgetInputChange(commentControllerHandle: number, input: string | undefined): Promise<number | undefined>;
+	$onActiveCommentThreadChange(commentControllerHandle: number, threadHandle: number | undefined): Promise<number | undefined>;
 	$provideCommentingRanges(commentControllerHandle: number, uriComponents: UriComponents, token: CancellationToken): Promise<IRange[] | undefined>;
 	$provideReactionGroup(commentControllerHandle: number): Promise<modes.CommentReaction[] | undefined>;
 	$toggleReaction(commentControllerHandle: number, threadHandle: number, uri: UriComponents, comment: modes.Comment, reaction: modes.CommentReaction): Promise<void>;
diff --git a/src/vs/workbench/api/common/extHostComments.ts b/src/vs/workbench/api/common/extHostComments.ts
index c22b84a8c19..5fd8d420b23 100644
--- a/src/vs/workbench/api/common/extHostComments.ts
+++ b/src/vs/workbench/api/common/extHostComments.ts
@@ -99,6 +99,17 @@ export class ExtHostComments implements ExtHostCommentsShape {
 		return Promise.resolve(commentControllerHandle);
 	}
 
+	$onActiveCommentThreadChange(commentControllerHandle: number, threadHandle: number): Promise<number | undefined> {
+		const commentController = this._commentControllers.get(commentControllerHandle);
+
+		if (!commentController) {
+			return Promise.resolve(undefined);
+		}
+
+		commentController.$onActiveCommentThreadChange(threadHandle);
+		return Promise.resolve(threadHandle);
+	}
+
 	$provideCommentingRanges(commentControllerHandle: number, uriComponents: UriComponents, token: CancellationToken): Promise<IRange[] | undefined> {
 		const commentController = this._commentControllers.get(commentControllerHandle);
 
@@ -563,6 +574,7 @@ class ExtHostCommentController implements vscode.CommentController {
 	}
 
 	public inputBox: ExtHostCommentInputBox | undefined;
+	public activeCommentThread: ExtHostCommentThread | undefined;
 	public activeCommentingRange?: vscode.Range;
 
 	public get handle(): number {
@@ -610,6 +622,10 @@ class ExtHostCommentController implements vscode.CommentController {
 		}
 	}
 
+	$onActiveCommentThreadChange(threadHandle: number) {
+		this.activeCommentThread = this.getCommentThread(threadHandle);
+	}
+
 	getCommentThread(handle: number) {
 		return this._threads.get(handle);
 	}