diff --git a/src/vs/workbench/contrib/chat/browser/chatInputWindow/chatInputWindowService.ts b/src/vs/workbench/contrib/chat/browser/chatInputWindow/chatInputWindowService.ts
index 03b205b0219a48..bba06d6c1471ec 100644
--- a/src/vs/workbench/contrib/chat/browser/chatInputWindow/chatInputWindowService.ts
+++ b/src/vs/workbench/contrib/chat/browser/chatInputWindow/chatInputWindowService.ts
@@ -72,6 +72,10 @@ const CHAT_INPUT_WINDOW_ACTION_WIDGET_HEIGHT = 420;
 const CHAT_INPUT_WINDOW_ACTION_WIDGET_WIDTH = 420;
 const CHAT_INPUT_WINDOW_ACTION_WIDGET_MARGIN = 4;
 const CHAT_INPUT_WINDOW_INITIAL_SURFACE_HEIGHT = 44;
+// Transparent gutter around the surface so the CSS window shadow is not clipped
+// by the frameless window bounds. Keep in sync with --omni-window-shadow-size in
+// media/chatInputWindow.css.
+const CHAT_INPUT_WINDOW_SHADOW_SIZE = 16;
 const CHAT_INPUT_WINDOW_MAX_PENDING_HEIGHT = 360;
 const CHAT_INPUT_WINDOW_MIN_CONFIRMATION_HEIGHT = 112;
 const CHAT_INPUT_WINDOW_CONTEXT_PICKER_TRANSITION_DELAY = 100;
@@ -684,14 +688,18 @@ export class ChatInputWindowService extends Disposable implements IChatInputWind
 				return;
 			}
 			lastContentHeight = contentHeight;
+			// Grow the window by the shadow gutter on all sides so the surface keeps
+			// its content size while the CSS shadow renders into the transparent band.
+			const windowWidth = width + 2 * CHAT_INPUT_WINDOW_SHADOW_SIZE;
+			const windowHeight = contentHeight + 2 * CHAT_INPUT_WINDOW_SHADOW_SIZE;
 			if (!didInitialPosition) {
 				didInitialPosition = true;
-				const initialBounds = this._positionedBounds(width, contentHeight);
+				const initialBounds = this._positionedBounds(windowWidth, windowHeight);
 				currentPosition = { x: initialBounds.x, y: initialBounds.y };
 			} else if (!applyingBounds) {
 				currentPosition = { x: win.screenX, y: win.screenY };
 			}
-			pendingBounds = { ...currentPosition, width, height: contentHeight };
+			pendingBounds = { ...currentPosition, width: windowWidth, height: windowHeight };
 			void applyPendingBounds();
 		};
 		this._fitWindowToContent = fitWindowToInput;
@@ -1614,7 +1622,10 @@ export class ChatInputWindowService extends Disposable implements IChatInputWind
 	}
 
 	private _defaultBounds(): IRectangle {
-		return this._positionedBounds(this._defaultWidth(), CHAT_INPUT_WINDOW_DEFAULT_HEIGHT);
+		return this._positionedBounds(
+			this._defaultWidth() + 2 * CHAT_INPUT_WINDOW_SHADOW_SIZE,
+			CHAT_INPUT_WINDOW_DEFAULT_HEIGHT + 2 * CHAT_INPUT_WINDOW_SHADOW_SIZE
+		);
 	}
 
 	private _positionedBounds(width: number, height: number): IRectangle {
diff --git a/src/vs/workbench/contrib/chat/browser/chatInputWindow/media/chatInputWindow.css b/src/vs/workbench/contrib/chat/browser/chatInputWindow/media/chatInputWindow.css
index ce12da1ed52118..450792da70ae52 100644
--- a/src/vs/workbench/contrib/chat/browser/chatInputWindow/media/chatInputWindow.css
+++ b/src/vs/workbench/contrib/chat/browser/chatInputWindow/media/chatInputWindow.css
@@ -7,11 +7,16 @@
 	--omni-rail: 20px;
 	--omni-icon-column: 16px;
 	--omni-row-gap: 8px;
+	/* Transparent gutter reserved so the window shadow can render without being
+	   clipped by the frameless window bounds. Keep in sync with
+	   CHAT_INPUT_WINDOW_SHADOW_SIZE in chatInputWindowService.ts. */
+	--omni-window-shadow-size: 16px;
 
 	box-sizing: border-box;
-	height: calc(100% - var(--vscode-strokeThickness) - var(--vscode-strokeThickness)) !important;
-	margin: var(--vscode-strokeThickness);
+	height: calc(100% - var(--omni-window-shadow-size) - var(--omni-window-shadow-size)) !important;
+	margin: var(--omni-window-shadow-size);
 	border-radius: var(--vscode-cornerRadius-xLarge);
+	box-shadow: 0 3px 10px 0 var(--vscode-widget-shadow, rgba(0, 0, 0, 0.36));
 	overflow: hidden;
 }