diff --git a/src/vs/workbench/api/common/extHostLanguageModelTools.ts b/src/vs/workbench/api/common/extHostLanguageModelTools.ts
index f3d03c9d08a..cf52a6f3e30 100644
--- a/src/vs/workbench/api/common/extHostLanguageModelTools.ts
+++ b/src/vs/workbench/api/common/extHostLanguageModelTools.ts
@@ -264,7 +264,6 @@ export class ExtHostLanguageModelTools implements ExtHostLanguageModelToolsShape
 		const options: vscode.LanguageModelToolInvocationStreamOptions<any> = {
 			rawInput: context.rawInput,
 			chatRequestId: context.chatRequestId,
-			chatSessionId: context.chatSessionId,
 			chatSessionResource: context.chatSessionResource,
 			chatInteractionId: context.chatInteractionId
 		};
diff --git a/src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts b/src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts
index 6aedfb31bfd..5caa093f45d 100644
--- a/src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts
+++ b/src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts
@@ -2008,7 +2008,6 @@ export class ChatWidget extends Disposable implements IChatWidget {
 
 		this._codeBlockModelCollection.clear();
 
-		this.container.setAttribute('data-session-id', model.sessionId);
 		this.viewModel = this.instantiationService.createInstance(ChatViewModel, model, this._codeBlockModelCollection, undefined);
 
 		// Pass input model reference to input part for state syncing
diff --git a/src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/chatViewPane.ts b/src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/chatViewPane.ts
index df7195252c1..a824546fe77 100644
--- a/src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/chatViewPane.ts
+++ b/src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/chatViewPane.ts
@@ -66,7 +66,9 @@ import { IChatEntitlementService } from '../../../../../services/chat/common/cha
 import { IWorkbenchEnvironmentService } from '../../../../../services/environment/common/environmentService.js';
 
 interface IChatViewPaneState extends Partial<IChatModelInputState> {
-	/** @deprecated */
+	/**
+	 * @deprecated This is kept around to support old view states. However it should not be set on new states and `sessionResource` should be used instead.
+	 */
 	sessionId?: string;
 	sessionResource?: URI;
 
@@ -695,7 +697,6 @@ export class ChatViewPane extends ViewPane implements IViewWelcomeDelegate {
 			await this.updateWidgetLockState(model.sessionResource); // Update widget lock state based on session type
 
 			// remember as model to restore in view state
-			this.viewState.sessionId = model.sessionId;
 			this.viewState.sessionResource = model.sessionResource;
 		}
 
diff --git a/src/vs/workbench/contrib/chat/common/chatService/chatServiceImpl.ts b/src/vs/workbench/contrib/chat/common/chatService/chatServiceImpl.ts
index e8df0b6017e..b28dbabe10c 100644
--- a/src/vs/workbench/contrib/chat/common/chatService/chatServiceImpl.ts
+++ b/src/vs/workbench/contrib/chat/common/chatService/chatServiceImpl.ts
@@ -866,7 +866,7 @@ export class ChatService extends Disposable implements IChatService {
 			agent: agentPart?.agent ?? defaultAgent,
 			agentSlashCommandPart,
 			commandPart,
-			sessionId: model.sessionId,
+			sessionResource: model.sessionResource,
 			location: model.initialLocation,
 			options,
 			enableCommandDetection
diff --git a/src/vs/workbench/contrib/chat/common/chatService/chatServiceTelemetry.ts b/src/vs/workbench/contrib/chat/common/chatService/chatServiceTelemetry.ts
index 6cd2769fbec..2a0f2cf7cc8 100644
--- a/src/vs/workbench/contrib/chat/common/chatService/chatServiceTelemetry.ts
+++ b/src/vs/workbench/contrib/chat/common/chatService/chatServiceTelemetry.ts
@@ -13,6 +13,7 @@ import { ChatAgentVoteDirection, ChatCopyKind, IChatSendRequestOptions, IChatUse
 import { isImageVariableEntry } from '../attachments/chatVariableEntries.js';
 import { ChatAgentLocation } from '../constants.js';
 import { ILanguageModelsService } from '../languageModels.js';
+import { chatSessionResourceToId } from '../model/chatUri.js';
 
 type ChatVoteEvent = {
 	direction: 'up' | 'down';
@@ -263,7 +264,7 @@ export class ChatRequestTelemetry {
 		agent: IChatAgentData;
 		agentSlashCommandPart: ChatRequestAgentSubcommandPart | undefined;
 		commandPart: ChatRequestSlashCommandPart | undefined;
-		sessionId: string;
+		sessionResource: URI;
 		location: ChatAgentLocation;
 		options: IChatSendRequestOptions | undefined;
 		enableCommandDetection: boolean;
@@ -294,7 +295,7 @@ export class ChatRequestTelemetry {
 			agent: detectedAgent?.id ?? this.opts.agent.id,
 			agentExtensionId: detectedAgent?.extensionId.value ?? this.opts.agent.extensionId.value,
 			slashCommand: this.opts.agentSlashCommandPart ? this.opts.agentSlashCommandPart.command.name : this.opts.commandPart?.slashCommand.command,
-			chatSessionId: this.opts.sessionId,
+			chatSessionId: chatSessionResourceToId(this.opts.sessionResource),
 			enableCommandDetection: this.opts.enableCommandDetection,
 			isParticipantDetected: !!detectedAgent,
 			location: this.opts.location,
diff --git a/src/vs/workbench/contrib/chat/common/tools/languageModelToolsService.ts b/src/vs/workbench/contrib/chat/common/tools/languageModelToolsService.ts
index 3316f148d31..d14a93696e0 100644
--- a/src/vs/workbench/contrib/chat/common/tools/languageModelToolsService.ts
+++ b/src/vs/workbench/contrib/chat/common/tools/languageModelToolsService.ts
@@ -349,8 +349,6 @@ export interface IToolInvocationStreamContext {
 	toolCallId: string;
 	rawInput: unknown;
 	chatRequestId?: string;
-	/** @deprecated Use {@link chatSessionResource} instead */
-	chatSessionId?: string;
 	chatSessionResource?: URI;
 	chatInteractionId?: string;
 }
diff --git a/src/vscode-dts/vscode.proposed.chatParticipantAdditions.d.ts b/src/vscode-dts/vscode.proposed.chatParticipantAdditions.d.ts
index 603f8a6fcb8..b23503fa232 100644
--- a/src/vscode-dts/vscode.proposed.chatParticipantAdditions.d.ts
+++ b/src/vscode-dts/vscode.proposed.chatParticipantAdditions.d.ts
@@ -1020,8 +1020,6 @@ declare module 'vscode' {
 		readonly rawInput?: unknown;
 
 		readonly chatRequestId?: string;
-		/** @deprecated Use {@link chatSessionResource} instead */
-		readonly chatSessionId?: string;
 		readonly chatSessionResource?: Uri;
 		readonly chatInteractionId?: string;
 	}