Add new exp TAS assignments endpoint (/api/v1/assignments) alongside legacy TAS

extensions/copilot/package.json

@@ -7304,7 +7304,7 @@
     "markdown-it": "^14.2.0",
     "minimatch": "^10.2.1",
     "undici": "^7.24.1",
-    "vscode-tas-client": "^0.1.84",
+    "vscode-tas-client": "^0.3.0",
     "web-tree-sitter": "^0.23.0"
   },
   "overrides": {

extensions/copilot/src/platform/authentication/common/copilotToken.ts

@@ -322,6 +322,7 @@ export interface Endpoints {
 	'origin-tracker'?: string;
 	proxy?: string;
 	telemetry?: string;
+	exp?: string;
 }
 
 //#endregion
@@ -431,6 +432,7 @@ const tokenEnvelopeValidator = vObj({
 		'origin-tracker': vString(),
 		proxy: vString(),
 		telemetry: vString(),
+		exp: vString(),
 	}),
 	enterprise_list: vNullable(vArray(vNumber())),
 	limited_user_quotas: vNullable(vObj({

extensions/copilot/src/platform/telemetry/common/baseTelemetryService.ts

@@ -163,6 +163,19 @@ export class BaseTelemetryService implements ITelemetryService {
 				"errortype": { "classification": "SystemMetaData", "purpose": "PerformanceAndHealth"}
 			}
 		*/
+		/* __GDPR__
+			"assignments-validation" : {
+				"FeatureVariableCount": { "classification": "SystemMetaData", "purpose": "FeatureInsight" },
+				"AssignedVariantCount": { "classification": "SystemMetaData", "purpose": "FeatureInsight" },
+				"DataVersion": { "classification": "SystemMetaData", "purpose": "FeatureInsight" },
+				"AssignmentContext": { "classification": "SystemMetaData", "purpose": "FeatureInsight" }
+			}
+		*/
+		/* __GDPR__
+			"call-assignments-error" : {
+				"ErrorType": { "classification": "SystemMetaData", "purpose": "PerformanceAndHealth"}
+			}
+		*/
 		if (name === 'abexp.assignmentcontext') {
 			this._setOriginalExpAssignments(value);
 			return;

extensions/copilot/src/platform/telemetry/node/baseExperimentationService.ts

@@ -8,7 +8,7 @@ import type { IExperimentationService as ITASExperimentationService } from 'vsco
 import { equals } from '../../../util/vs/base/common/arrays';
 import { IntervalTimer } from '../../../util/vs/base/common/async';
 import { Emitter } from '../../../util/vs/base/common/event';
-import { Disposable } from '../../../util/vs/base/common/lifecycle';
+import { Disposable, MutableDisposable, toDisposable } from '../../../util/vs/base/common/lifecycle';
 import { ICopilotTokenStore } from '../../authentication/common/copilotTokenStore';
 import { IConfigurationService } from '../../configuration/common/configurationService';
 import { IVSCodeExtensionContext } from '../../extContext/common/extensionContext';
@@ -124,9 +124,15 @@ export class BaseExperimentationService extends Disposable implements IExperimen
 	private readonly _refreshTimer = this._register(new IntervalTimer());
 	private readonly _previouslyReadTreatments = new Map<string, boolean | string | number | undefined>();
 
-	protected readonly _delegate: ITASExperimentationService;
+	protected _delegate: ITASExperimentationService;
 	protected readonly _userInfoStore: UserInfoStore;
 
+	/** Disposes the current delegate (stopping its polling); auto-disposes the previous one on replacement. */
+	private readonly _delegateDisposable = this._register(new MutableDisposable());
+
+	private readonly _delegateFn: TASClientDelegateFn;
+	private readonly _globalState: vscode.Memento;
+
 	protected _onDidTreatmentsChange = this._register(new Emitter<TreatmentsChangeEvent>());
 	readonly onDidTreatmentsChange = this._onDidTreatmentsChange.event;
 
@@ -155,10 +161,26 @@ export class BaseExperimentationService extends Disposable implements IExperimen
 			this._signalTreatmentsChangeEvent();
 		}, 60 * 60 * 1000);
 
-		this._delegate = delegateFn(context.globalState, this._userInfoStore);
-		this._delegate.initialFetch.then(() => {
+		this._delegateFn = delegateFn;
+		this._globalState = context.globalState;
+		this._delegate = this._createDelegate();
+	}
+
+	private _createDelegate(): ITASExperimentationService {
+		const delegate = this._delegateFn(this._globalState, this._userInfoStore);
+		this._delegateDisposable.value = toDisposable(() => (delegate as unknown as { dispose?(): void }).dispose?.());
+		delegate.initialFetch.then(() => {
 			this._logService.trace(`[BaseExperimentationService] Initial fetch completed`);
 		});
+		return delegate;
+	}
+
+	/**
+	 * Creates a fresh delegate, disposing the previous one (stopping its polling). Used
+	 * when inputs captured at delegate-creation time (e.g. the assignments endpoint) change.
+	 */
+	protected recreateDelegate(): void {
+		this._delegate = this._createDelegate();
 	}
 
 	private _signalTreatmentsChangeEvent = () => {

extensions/copilot/src/platform/telemetry/test/node/experimentation.spec.ts

@@ -127,6 +127,8 @@ class MockTASExperimentationService implements ITASExperimentationService {
 		this.refreshCallCount = 0;
 		this.treatmentRequests = [];
 	}
+
+	dispose(): void { }
 }
 
 describe('ExP Service Tests', () => {

extensions/copilot/src/platform/telemetry/vscode-node/microsoftExperimentationService.ts

@@ -5,7 +5,7 @@
 
 import path from 'path';
 import * as vscode from 'vscode';
-import { getExperimentationService, IExperimentationFilterProvider, TargetPopulation } from 'vscode-tas-client';
+import { getExperimentationServiceFromConfig, IExperimentationFilterProvider, TargetPopulation } from 'vscode-tas-client';
 import { platform, PlatformToString } from '../../../util/vs/base/common/platform';
 import { isObject } from '../../../util/vs/base/common/types';
 import { ICopilotTokenStore } from '../../authentication/common/copilotTokenStore';
@@ -31,6 +31,34 @@ function trimVersionSuffix(version: string): string {
 	return version.split('-')[0];
 }
 
+/**
+ * Formats an ISO date into the `yyyymmddHH` form the experimentation backend expects
+ * (10 digits, fits within int32). Returns an empty string when unavailable.
+ */
+function formatReleaseDate(iso: string): string {
+	if (!iso) {
+		return '';
+	}
+	const match = /^([0-9]{4})-([0-9]{2})-([0-9]{2})T([0-9]{2})/.exec(iso);
+	if (!match) {
+		return '';
+	}
+	return match.slice(1, 5).join('');
+}
+
+/**
+ * Reads and formats the product release date from `product.json`, or `undefined` on failure.
+ */
+function readReleaseDate(logService: ILogService, tag: string): string | undefined {
+	try {
+		const product = require(path.join(vscode.env.appRoot, 'product.json'));
+		return formatReleaseDate(product.date ?? '');
+	} catch (error) {
+		logService.warn(`${tag} Failed to read product.json for release date: ${error}`);
+		return undefined;
+	}
+}
+
 const CopilotRelatedPluginVersionPrefix = 'X-Copilot-RelatedPluginVersion-';
 
 export enum RelatedExtensionsFilter {
@@ -159,28 +187,7 @@ class PlatformAndReleaseDateFilterProvider implements IExperimentationFilterProv
 	constructor(
 		private _logService: ILogService
 	) {
-		this._releaseDate = this._initReleaseDate();
-	}
-
-	private _initReleaseDate(): string | undefined {
-		try {
-			const product = require(path.join(vscode.env.appRoot, 'product.json'));
-			return this._formatReleaseDate(product.date ?? '');
-		} catch (error) {
-			this._logService.warn(`[PlatformAndReleaseDateFilterProvider]::_initReleaseDate Failed to read product.json for release date: ${error}`);
-			return undefined;
-		}
-	}
-
-	private _formatReleaseDate(iso: string): string {
-		if (!iso) {
-			return '';
-		}
-		const match = /^([0-9]{4})-([0-9]{2})-([0-9]{2})T([0-9]{2})/.exec(iso);
-		if (!match) {
-			return '';
-		}
-		return match.slice(1, 5).join('');
+		this._releaseDate = readReleaseDate(_logService, '[PlatformAndReleaseDateFilterProvider]::readReleaseDate');
 	}
 
 	getFilters(): Map<string, string> {
@@ -215,6 +222,46 @@ class WindowKindFilterProvider implements IExperimentationFilterProvider {
 	}
 }
 
+/**
+ * Emits the Copilot-side filters for the new TAS assignments API (POST /api/v1/assignments)
+ * using the new userParam key names. Reads the Copilot token fresh on each call so refreshed
+ * assignments pick up account changes. The generic `vscode_core_*` app/build/extension/target
+ * filters are added automatically by `vscode-tas-client`.
+ */
+class CopilotAssignmentsFilterProvider implements IExperimentationFilterProvider {
+	private readonly _releaseDate: string | undefined;
+
+	constructor(
+		private readonly _copilotTokenStore: ICopilotTokenStore,
+		private readonly _logService: ILogService
+	) {
+		this._releaseDate = readReleaseDate(_logService, '[CopilotAssignmentsFilterProvider]::readReleaseDate');
+	}
+
+	getFilters(): Map<string, string | undefined> {
+		const token = this._copilotTokenStore.copilotToken;
+		const internalOrg = token
+			? (token.isVscodeTeamMember ? 'vscode' : token.isGitHubInternal ? 'github' : token.isMicrosoftInternal ? 'microsoft' : undefined)
+			: undefined;
+
+		const filters = new Map<string, string | undefined>();
+		filters.set('vscode_core_platform', PlatformToString(platform));
+		if (this._releaseDate) {
+			filters.set('vscode_core_releasedate', this._releaseDate);
+		}
+		filters.set('vscode_core_windowkind', vscode.workspace.isAgentSessionsWorkspace ? 'agents' : 'editor');
+		filters.set('devdeviceid', vscode.env.devDeviceId);
+		filters.set('copilottrackingid', token?.getTokenValue('tid'));
+		filters.set('github_core_organizationid', token?.organizationList.join(','));
+		filters.set('github_core_businessid', token?.enterpriseList.join(','));
+		filters.set('github_core_isghormsftstaff', internalOrg ? '1' : '0');
+		filters.set('github_core_ghmsftorexternal', internalOrg === 'github' ? 'github' : (internalOrg === 'microsoft' || internalOrg === 'vscode') ? 'microsoft' : 'external');
+
+		this._logService.trace(`[CopilotAssignmentsFilterProvider]::getFilters Filters: ${JSON.stringify(Array.from(filters.entries()))}`);
+		return filters;
+	}
+}
+
 export class MicrosoftExperimentationService extends BaseExperimentationService {
 	constructor(
 		@ITelemetryService telemetryService: ITelemetryService,
@@ -232,27 +279,55 @@ export class MicrosoftExperimentationService extends BaseExperimentationService
 		let self: MicrosoftExperimentationService | undefined = undefined;
 		const delegateFn = (globalState: vscode.Memento, userInfoStore: UserInfoStore) => {
 			const wrappedMemento = new ExpMementoWrapper(globalState, envService);
-			return getExperimentationService(
-				id,
-				version,
+			const exp = copilotTokenStore.copilotToken?.endpoints?.exp;
+			const assignmentsEndpoint = exp ? `${exp.replace(/\/+$/, '')}/api/v1/assignments` : undefined;
+			// Route the assignments request through the extension's fetcher service so it gets
+			// proxy handling, retries/fallback, and the standard user-agent for free.
+			const assignmentsFetch = (url: string, init: { method: 'POST'; headers: Record<string, string>; body: string }) =>
+				fetcherService.fetch(url, {
+					method: init.method,
+					headers: init.headers,
+					body: init.body,
+					callSite: 'exp.assignments',
+				});
+			return getExperimentationServiceFromConfig({
+				extensionName: id,
+				extensionVersion: version,
 				targetPopulation,
-				telemetryService,
-				wrappedMemento,
-				new GithubAccountFilterProvider(userInfoStore, logService),
-				new RelatedExtensionsFilterProvider(logService),
-				new CopilotExtensionsFilterProvider(logService),
-				// The callback is called in super ctor. At that time, self/this is not initialized yet (but also, no filter could have been possibly set).
-				new CopilotCompletionsFilterProvider(() => self?.getCompletionsFilters() ?? new Map(), logService),
-				new DevDeviceIdFilterProvider(vscode.env.devDeviceId),
-				new PlatformAndReleaseDateFilterProvider(logService),
-				new WindowKindFilterProvider(logService),
-			);
+				telemetry: telemetryService,
+				memento: wrappedMemento,
+				filterProviders: [
+					new GithubAccountFilterProvider(userInfoStore, logService),
+					new RelatedExtensionsFilterProvider(logService),
+					new CopilotExtensionsFilterProvider(logService),
+					// The callback is called in super ctor. At that time, self/this is not initialized yet (but also, no filter could have been possibly set).
+					new CopilotCompletionsFilterProvider(() => self?.getCompletionsFilters() ?? new Map(), logService),
+					new DevDeviceIdFilterProvider(vscode.env.devDeviceId),
+					new PlatformAndReleaseDateFilterProvider(logService),
+					new WindowKindFilterProvider(logService),
+				],
+				assignmentsEndpoint,
+				assignmentsFilterProviders: assignmentsEndpoint ? [new CopilotAssignmentsFilterProvider(copilotTokenStore, logService)] : undefined,
+				assignmentsFetch: assignmentsEndpoint ? assignmentsFetch : undefined,
+			});
 		};
 
 		super(delegateFn, context, copilotTokenStore, configurationService, logService);
 
 		self = this; // This is now fully initialized.
 
+		// The assignments endpoint is sourced from the Copilot token, which may arrive after
+		// this service is created. Recreate the delegate when its `exp` endpoint changes.
+		let currentExp = copilotTokenStore.copilotToken?.endpoints?.exp;
+		this._register(copilotTokenStore.onDidStoreUpdate(() => {
+			const token = copilotTokenStore.copilotToken;
+			const newExp = token?.endpoints?.exp;
+			if (newExp !== currentExp) {
+				currentExp = newExp;
+				this.recreateDelegate();
+			}
+		}));
+
 		if (fetcherService instanceof FetcherService) {
 			fetcherService.setExperimentationService(this);
 		}

package.json

@@ -156,7 +156,7 @@
     "playwright-core": "1.61.0-alpha-2026-06-04",
     "ssh2": "^1.16.0",
     "tar": "^7.5.20",
-    "tas-client": "0.3.1",
+    "tas-client": "0.4.2",
     "undici": "^7.28.0",
     "vscode-oniguruma": "1.7.0",
     "vscode-regexpp": "^3.1.0",