diff --git a/src/vs/workbench/api/browser/mainThreadChatSessions.ts b/src/vs/workbench/api/browser/mainThreadChatSessions.ts
index da9a664e813..47bff4e1d83 100644
--- a/src/vs/workbench/api/browser/mainThreadChatSessions.ts
+++ b/src/vs/workbench/api/browser/mainThreadChatSessions.ts
@@ -354,13 +354,9 @@ class MainThreadChatSessionItemController extends Disposable implements IChatSes
 		this._onDidChangeChatSessionItems.fire();
 	}
 
-	updateItem(item: IChatSessionItem): void {
-		if (this._items.has(item.resource)) {
-			this._items.set(item.resource, item);
-			this._onDidChangeChatSessionItems.fire();
-		} else {
-			console.warn(`Item with resource ${item.resource.toString()} does not exist. Skipping update.`);
-		}
+	addOrUpdateItem(item: IChatSessionItem): void {
+		this._items.set(item.resource, item);
+		this._onDidChangeChatSessionItems.fire();
 	}
 
 	fireOnDidChangeChatSessionItems(): void {
@@ -440,8 +436,17 @@ export class MainThreadChatSessions extends Disposable implements MainThreadChat
 		));
 	}
 
+	private getController(handle: number): MainThreadChatSessionItemController {
+		const registration = this._itemControllerRegistrations.get(handle);
+		if (!registration) {
+			throw new Error(`No chat session controller registered for handle ${handle}`);
+		}
+		return registration.controller;
+	}
+
 	$onDidChangeChatSessionItems(handle: number): void {
-		this._itemControllerRegistrations.get(handle)?.controller.fireOnDidChangeChatSessionItems();
+		const controller = this.getController(handle);
+		controller.fireOnDidChangeChatSessionItems();
 	}
 
 	private async _resolveSessionItem(item: Dto<IChatSessionItem>): Promise<IChatSessionItem> {
@@ -474,31 +479,20 @@ export class MainThreadChatSessions extends Disposable implements MainThreadChat
 		};
 	}
 
-	async $setChatSessionItems(handle: number, items: Dto<IChatSessionItem>[]): Promise<void> {
-		const registration = this._itemControllerRegistrations.get(handle);
-		if (!registration) {
-			this._logService.warn(`No chat session controller registered for handle ${handle}`);
-			return;
-		}
-
+	async $setChatSessionItems(controllerHandle: number, items: Dto<IChatSessionItem>[]): Promise<void> {
+		const controller = this.getController(controllerHandle);
 		const resolvedItems = await Promise.all(items.map(item => this._resolveSessionItem(item)));
-		registration.controller.setItems(resolvedItems);
+		controller.setItems(resolvedItems);
 	}
 
-	async $updateChatSessionItem(controllerHandle: number, item: Dto<IChatSessionItem>): Promise<void> {
-		const registration = this._itemControllerRegistrations.get(controllerHandle);
-		if (!registration) {
-			this._logService.warn(`No chat session controller registered for handle ${controllerHandle}`);
-			return;
-		}
-
+	async $addOrUpdateChatSessionItem(controllerHandle: number, item: Dto<IChatSessionItem>): Promise<void> {
+		const controller = this.getController(controllerHandle);
 		const resolvedItem = await this._resolveSessionItem(item);
-		registration.controller.updateItem(resolvedItem);
+		controller.addOrUpdateItem(resolvedItem);
 	}
 
 	$onDidChangeChatSessionOptions(handle: number, sessionResourceComponents: UriComponents, updates: ReadonlyArray<{ optionId: string; value: string }>): void {
 		const sessionResource = URI.revive(sessionResourceComponents);
-
 		this._chatSessionsService.notifySessionOptionsChange(sessionResource, updates);
 	}
 
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index 422aa1b5827..d12f99c0051 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -3418,7 +3418,7 @@ export interface MainThreadChatSessionsShape extends IDisposable {
 	$registerChatSessionItemController(handle: number, chatSessionType: string): void;
 	$unregisterChatSessionItemController(handle: number): void;
 	$setChatSessionItems(handle: number, items: Dto<IChatSessionItem>[]): Promise<void>;
-	$updateChatSessionItem(handle: number, item: Dto<IChatSessionItem>): Promise<void>;
+	$addOrUpdateChatSessionItem(handle: number, item: Dto<IChatSessionItem>): Promise<void>;
 	$onDidChangeChatSessionItems(handle: number): void;
 	$onDidCommitChatSessionItem(handle: number, original: UriComponents, modified: UriComponents): void;
 	$registerChatSessionContentProvider(handle: number, chatSessionScheme: string): void;
diff --git a/src/vs/workbench/api/common/extHostChatSessions.ts b/src/vs/workbench/api/common/extHostChatSessions.ts
index cec3c62b015..8868ad66110 100644
--- a/src/vs/workbench/api/common/extHostChatSessions.ts
+++ b/src/vs/workbench/api/common/extHostChatSessions.ts
@@ -176,12 +176,17 @@ class ChatSessionItemImpl implements vscode.ChatSessionItem {
 	}
 }
 
+interface SessionCollectionListeners {
+	onItemsChanged(): void;
+	onItemAddedOrUpdated(item: vscode.ChatSessionItem): void;
+}
+
 class ChatSessionItemCollectionImpl implements vscode.ChatSessionItemCollection {
 	readonly #items = new ResourceMap<vscode.ChatSessionItem>();
-	#onItemsChanged: () => void;
+	readonly #callbacks: SessionCollectionListeners;
 
-	constructor(onItemsChanged: () => void) {
-		this.#onItemsChanged = onItemsChanged;
+	constructor(callbacks: SessionCollectionListeners) {
+		this.#callbacks = callbacks;
 	}
 
 	get size(): number {
@@ -197,7 +202,7 @@ class ChatSessionItemCollectionImpl implements vscode.ChatSessionItemCollection
 		for (const item of items) {
 			this.#items.set(item.resource, item);
 		}
-		this.#onItemsChanged();
+		this.#callbacks.onItemsChanged();
 	}
 
 	forEach(callback: (item: vscode.ChatSessionItem, collection: vscode.ChatSessionItemCollection) => unknown, thisArg?: any): void {
@@ -207,13 +212,20 @@ class ChatSessionItemCollectionImpl implements vscode.ChatSessionItemCollection
 	}
 
 	add(item: vscode.ChatSessionItem): void {
+		const existing = this.#items.get(item.resource);
+		if (existing && existing === item) {
+			// We're adding the same item again
+			return;
+		}
+
 		this.#items.set(item.resource, item);
-		this.#onItemsChanged();
+		this.#callbacks.onItemAddedOrUpdated(item);
 	}
 
 	delete(resource: vscode.Uri): void {
-		this.#items.delete(resource);
-		this.#onItemsChanged();
+		if (this.#items.delete(resource)) {
+			this.#callbacks.onItemsChanged();
+		}
 	}
 
 	get(resource: vscode.Uri): vscode.ChatSessionItem | undefined {
@@ -324,8 +336,10 @@ export class ExtHostChatSessions extends Disposable implements ExtHostChatSessio
 
 		const onDidChangeChatSessionItemStateEmitter = disposables.add(new Emitter<vscode.ChatSessionItem>());
 
-		const collection = new ChatSessionItemCollectionImpl(() => {
+		const collection = new ChatSessionItemCollectionImpl({
 			// Noop for providers
+			onItemsChanged: () => { },
+			onItemAddedOrUpdated: () => { }
 		});
 
 		// Helper to push items to main thread
@@ -400,7 +414,12 @@ export class ExtHostChatSessions extends Disposable implements ExtHostChatSessio
 			void this._proxy.$setChatSessionItems(controllerHandle, items);
 		};
 
-		const collection = new ChatSessionItemCollectionImpl(onItemsChanged);
+		const collection = new ChatSessionItemCollectionImpl({
+			onItemsChanged,
+			onItemAddedOrUpdated: (item: vscode.ChatSessionItem) => {
+				void this._proxy.$addOrUpdateChatSessionItem(controllerHandle, typeConvert.ChatSessionItem.from(item));
+			}
+		});
 
 		const controller = Object.freeze<vscode.ChatSessionItemController>({
 			id,
@@ -420,7 +439,10 @@ export class ExtHostChatSessions extends Disposable implements ExtHostChatSessio
 				}
 
 				const item = new ChatSessionItemImpl(resource, label, () => {
-					void this._proxy.$updateChatSessionItem(controllerHandle, typeConvert.ChatSessionItem.from(item));
+					// Make sure the item really is in the collection. If not we don't need to transmit it to the main thread yet
+					if (collection.get(resource) === item) {
+						void this._proxy.$addOrUpdateChatSessionItem(controllerHandle, typeConvert.ChatSessionItem.from(item));
+					}
 				});
 				return item;
 			},