feat(ai): route copilot claude via anthropic messages api

packages/ai/scripts/generate-models.ts

@@ -519,13 +519,21 @@ async function loadModelsDevData(): Promise<Model<any>[]> {
 				if (m.tool_call !== true) continue;
 				if (m.status === "deprecated") continue;
 
+				// Claude 4.x models route to Anthropic Messages API
+				const isCopilotClaude4 = /^claude-(haiku|sonnet|opus)-4([.\-]|$)/.test(modelId);
 				// gpt-5 models require responses API, others use completions
 				const needsResponsesApi = modelId.startsWith("gpt-5") || modelId.startsWith("oswe");
 
+				const api: Api = isCopilotClaude4
+					? "anthropic-messages"
+					: needsResponsesApi
+						? "openai-responses"
+						: "openai-completions";
+
 				const copilotModel: Model<any> = {
 					id: modelId,
 					name: m.name || modelId,
-					api: needsResponsesApi ? "openai-responses" : "openai-completions",
+					api,
 					provider: "github-copilot",
 					baseUrl: "https://api.individual.githubcopilot.com",
 					reasoning: m.reasoning === true,
@@ -540,13 +548,13 @@ async function loadModelsDevData(): Promise<Model<any>[]> {
 					maxTokens: m.limit?.output || 8192,
 					headers: { ...COPILOT_STATIC_HEADERS },
 					// compat only applies to openai-completions
-					...(needsResponsesApi ? {} : {
+					...(api === "openai-completions" ? {
 						compat: {
 							supportsStore: false,
 							supportsDeveloperRole: false,
 							supportsReasoningEffort: false,
 						},
-					}),
+					} : {}),
 				};
 
 				models.push(copilotModel);

packages/ai/src/models.generated.ts

@@ -2260,11 +2260,10 @@ export const MODELS = {
 		"claude-haiku-4.5": {
 			id: "claude-haiku-4.5",
 			name: "Claude Haiku 4.5",
-			api: "openai-completions",
+			api: "anthropic-messages",
 			provider: "github-copilot",
 			baseUrl: "https://api.individual.githubcopilot.com",
 			headers: {"User-Agent":"GitHubCopilotChat/0.35.0","Editor-Version":"vscode/1.107.0","Editor-Plugin-Version":"copilot-chat/0.35.0","Copilot-Integration-Id":"vscode-chat"},
-			compat: {"supportsStore":false,"supportsDeveloperRole":false,"supportsReasoningEffort":false},
 			reasoning: true,
 			input: ["text", "image"],
 			cost: {
@@ -2275,15 +2274,14 @@ export const MODELS = {
 			},
 			contextWindow: 128000,
 			maxTokens: 16000,
-		} satisfies Model<"openai-completions">,
+		} satisfies Model<"anthropic-messages">,
 		"claude-opus-4.5": {
 			id: "claude-opus-4.5",
 			name: "Claude Opus 4.5",
-			api: "openai-completions",
+			api: "anthropic-messages",
 			provider: "github-copilot",
 			baseUrl: "https://api.individual.githubcopilot.com",
 			headers: {"User-Agent":"GitHubCopilotChat/0.35.0","Editor-Version":"vscode/1.107.0","Editor-Plugin-Version":"copilot-chat/0.35.0","Copilot-Integration-Id":"vscode-chat"},
-			compat: {"supportsStore":false,"supportsDeveloperRole":false,"supportsReasoningEffort":false},
 			reasoning: true,
 			input: ["text", "image"],
 			cost: {
@@ -2294,15 +2292,14 @@ export const MODELS = {
 			},
 			contextWindow: 128000,
 			maxTokens: 16000,
-		} satisfies Model<"openai-completions">,
+		} satisfies Model<"anthropic-messages">,
 		"claude-opus-4.6": {
 			id: "claude-opus-4.6",
 			name: "Claude Opus 4.6",
-			api: "openai-completions",
+			api: "anthropic-messages",
 			provider: "github-copilot",
 			baseUrl: "https://api.individual.githubcopilot.com",
 			headers: {"User-Agent":"GitHubCopilotChat/0.35.0","Editor-Version":"vscode/1.107.0","Editor-Plugin-Version":"copilot-chat/0.35.0","Copilot-Integration-Id":"vscode-chat"},
-			compat: {"supportsStore":false,"supportsDeveloperRole":false,"supportsReasoningEffort":false},
 			reasoning: true,
 			input: ["text", "image"],
 			cost: {
@@ -2313,15 +2310,14 @@ export const MODELS = {
 			},
 			contextWindow: 128000,
 			maxTokens: 64000,
-		} satisfies Model<"openai-completions">,
+		} satisfies Model<"anthropic-messages">,
 		"claude-sonnet-4": {
 			id: "claude-sonnet-4",
 			name: "Claude Sonnet 4",
-			api: "openai-completions",
+			api: "anthropic-messages",
 			provider: "github-copilot",
 			baseUrl: "https://api.individual.githubcopilot.com",
 			headers: {"User-Agent":"GitHubCopilotChat/0.35.0","Editor-Version":"vscode/1.107.0","Editor-Plugin-Version":"copilot-chat/0.35.0","Copilot-Integration-Id":"vscode-chat"},
-			compat: {"supportsStore":false,"supportsDeveloperRole":false,"supportsReasoningEffort":false},
 			reasoning: true,
 			input: ["text", "image"],
 			cost: {
@@ -2332,15 +2328,14 @@ export const MODELS = {
 			},
 			contextWindow: 128000,
 			maxTokens: 16000,
-		} satisfies Model<"openai-completions">,
+		} satisfies Model<"anthropic-messages">,
 		"claude-sonnet-4.5": {
 			id: "claude-sonnet-4.5",
 			name: "Claude Sonnet 4.5",
-			api: "openai-completions",
+			api: "anthropic-messages",
 			provider: "github-copilot",
 			baseUrl: "https://api.individual.githubcopilot.com",
 			headers: {"User-Agent":"GitHubCopilotChat/0.35.0","Editor-Version":"vscode/1.107.0","Editor-Plugin-Version":"copilot-chat/0.35.0","Copilot-Integration-Id":"vscode-chat"},
-			compat: {"supportsStore":false,"supportsDeveloperRole":false,"supportsReasoningEffort":false},
 			reasoning: true,
 			input: ["text", "image"],
 			cost: {
@@ -2351,7 +2346,7 @@ export const MODELS = {
 			},
 			contextWindow: 128000,
 			maxTokens: 16000,
-		} satisfies Model<"openai-completions">,
+		} satisfies Model<"anthropic-messages">,
 		"gemini-2.5-pro": {
 			id: "gemini-2.5-pro",
 			name: "Gemini 2.5 Pro",

packages/ai/src/providers/anthropic.ts

@@ -28,6 +28,7 @@ import { AssistantMessageEventStream } from "../utils/event-stream.js";
 import { parseStreamingJson } from "../utils/json-parse.js";
 import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
 
+import { buildCopilotDynamicHeaders, hasCopilotVisionInput } from "./github-copilot-headers.js";
 import { adjustMaxTokensForThinking, buildBaseOptions } from "./simple-options.js";
 import { transformMessages } from "./transform-messages.js";
 
@@ -217,11 +218,22 @@ export const streamAnthropic: StreamFunction<"anthropic-messages", AnthropicOpti
 
 		try {
 			const apiKey = options?.apiKey ?? getEnvApiKey(model.provider) ?? "";
+
+			let copilotDynamicHeaders: Record<string, string> | undefined;
+			if (model.provider === "github-copilot") {
+				const hasImages = hasCopilotVisionInput(context.messages);
+				copilotDynamicHeaders = buildCopilotDynamicHeaders({
+					messages: context.messages,
+					hasImages,
+				});
+			}
+
 			const { client, isOAuthToken } = createClient(
 				model,
 				apiKey,
 				options?.interleavedThinking ?? true,
 				options?.headers,
+				copilotDynamicHeaders,
 			);
 			const params = buildParams(model, context, isOAuthToken, options);
 			options?.onPayload?.(params);
@@ -471,12 +483,54 @@ function isOAuthToken(apiKey: string): boolean {
 	return apiKey.includes("sk-ant-oat");
 }
 
-function createClient(
+export interface BuildAnthropicClientOptionsParams {
-	model: Model<"anthropic-messages">,
+	model: Model<"anthropic-messages">;
-	apiKey: string,
+	apiKey: string;
-	interleavedThinking: boolean,
+	interleavedThinking: boolean;
-	optionsHeaders?: Record<string, string>,
+	dynamicHeaders?: Record<string, string>;
-): { client: Anthropic; isOAuthToken: boolean } {
+	optionsHeaders?: Record<string, string>;
+}
+
+export interface AnthropicClientConfig {
+	apiKey: string | null;
+	authToken?: string;
+	baseURL: string;
+	defaultHeaders: Record<string, string>;
+	dangerouslyAllowBrowser: boolean;
+	isOAuthToken: boolean;
+}
+
+export function buildAnthropicClientOptions(params: BuildAnthropicClientOptionsParams): AnthropicClientConfig {
+	const { model, apiKey, interleavedThinking, dynamicHeaders, optionsHeaders } = params;
+
+	// Copilot: Bearer auth, selective betas
+	if (model.provider === "github-copilot") {
+		const betaFeatures: string[] = [];
+		if (interleavedThinking) {
+			betaFeatures.push("interleaved-thinking-2025-05-14");
+		}
+
+		const defaultHeaders = mergeHeaders(
+			{
+				accept: "application/json",
+				"anthropic-dangerous-direct-browser-access": "true",
+				...(betaFeatures.length > 0 ? { "anthropic-beta": betaFeatures.join(",") } : {}),
+				Authorization: `Bearer ${apiKey}`,
+			},
+			dynamicHeaders,
+			model.headers,
+			optionsHeaders,
+		);
+
+		return {
+			apiKey: null,
+			baseURL: model.baseUrl,
+			defaultHeaders,
+			dangerouslyAllowBrowser: true,
+			isOAuthToken: false,
+		};
+	}
+
 	const betaFeatures = ["fine-grained-tool-streaming-2025-05-14"];
 	if (interleavedThinking) {
 		betaFeatures.push("interleaved-thinking-2025-05-14");
@@ -484,7 +538,6 @@ function createClient(
 
 	const oauthToken = isOAuthToken(apiKey);
 	if (oauthToken) {
-		// Stealth mode: Mimic Claude Code's headers exactly
 		const defaultHeaders = mergeHeaders(
 			{
 				accept: "application/json",
@@ -497,15 +550,14 @@ function createClient(
 			optionsHeaders,
 		);
 
-		const client = new Anthropic({
+		return {
 			apiKey: null,
 			authToken: apiKey,
 			baseURL: model.baseUrl,
 			defaultHeaders,
 			dangerouslyAllowBrowser: true,
-		});
+			isOAuthToken: true,
-
+		};
-		return { client, isOAuthToken: true };
 	}
 
 	const defaultHeaders = mergeHeaders(
@@ -518,14 +570,39 @@ function createClient(
 		optionsHeaders,
 	);
 
-	const client = new Anthropic({
+	return {
 		apiKey,
 		baseURL: model.baseUrl,
-		dangerouslyAllowBrowser: true,
 		defaultHeaders,
+		dangerouslyAllowBrowser: true,
+		isOAuthToken: false,
+	};
+}
+
+function createClient(
+	model: Model<"anthropic-messages">,
+	apiKey: string,
+	interleavedThinking: boolean,
+	optionsHeaders?: Record<string, string>,
+	dynamicHeaders?: Record<string, string>,
+): { client: Anthropic; isOAuthToken: boolean } {
+	const config = buildAnthropicClientOptions({
+		model,
+		apiKey,
+		interleavedThinking,
+		dynamicHeaders,
+		optionsHeaders,
 	});
 
-	return { client, isOAuthToken: false };
+	const client = new Anthropic({
+		apiKey: config.apiKey,
+		...(config.authToken ? { authToken: config.authToken } : {}),
+		baseURL: config.baseURL,
+		defaultHeaders: config.defaultHeaders,
+		dangerouslyAllowBrowser: config.dangerouslyAllowBrowser,
+	});
+
+	return { client, isOAuthToken: config.isOAuthToken };
 }
 
 function buildParams(

packages/ai/src/providers/github-copilot-headers.ts

@@ -0,0 +1,59 @@
+import type { Message } from "../types.js";
+
+/**
+ * Infer whether the current request to Copilot is user-initiated or agent-initiated.
+ * Accepts `unknown[]` because providers may pass pre-converted message shapes.
+ */
+export function inferCopilotInitiator(messages: unknown[]): "user" | "agent" {
+	if (messages.length === 0) return "user";
+
+	const last = messages[messages.length - 1] as Record<string, unknown>;
+	const role = last.role as string | undefined;
+	if (!role) return "user";
+
+	if (role !== "user") return "agent";
+
+	// Check if last content block is a tool_result (Anthropic-converted shape)
+	const content = last.content;
+	if (Array.isArray(content) && content.length > 0) {
+		const lastBlock = content[content.length - 1] as Record<string, unknown>;
+		if (lastBlock.type === "tool_result") {
+			return "agent";
+		}
+	}
+
+	return "user";
+}
+
+/** Check whether any message in the conversation contains image content. */
+export function hasCopilotVisionInput(messages: Message[]): boolean {
+	return messages.some((msg) => {
+		if (msg.role === "user" && Array.isArray(msg.content)) {
+			return msg.content.some((c) => c.type === "image");
+		}
+		if (msg.role === "toolResult" && Array.isArray(msg.content)) {
+			return msg.content.some((c) => c.type === "image");
+		}
+		return false;
+	});
+}
+
+/**
+ * Build dynamic Copilot headers that vary per-request.
+ * Static headers (User-Agent, Editor-Version, etc.) come from model.headers.
+ */
+export function buildCopilotDynamicHeaders(params: {
+	messages: unknown[];
+	hasImages: boolean;
+}): Record<string, string> {
+	const headers: Record<string, string> = {
+		"X-Initiator": inferCopilotInitiator(params.messages),
+		"Openai-Intent": "conversation-edits",
+	};
+
+	if (params.hasImages) {
+		headers["Copilot-Vision-Request"] = "true";
+	}
+
+	return headers;
+}

packages/ai/src/providers/openai-completions.ts

@@ -29,6 +29,7 @@ import type {
 import { AssistantMessageEventStream } from "../utils/event-stream.js";
 import { parseStreamingJson } from "../utils/json-parse.js";
 import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
+import { buildCopilotDynamicHeaders, hasCopilotVisionInput } from "./github-copilot-headers.js";
 import { buildBaseOptions, clampReasoning } from "./simple-options.js";
 import { transformMessages } from "./transform-messages.js";
 
@@ -359,28 +360,12 @@ function createClient(
 
 	const headers = { ...model.headers };
 	if (model.provider === "github-copilot") {
-		// Copilot expects X-Initiator to indicate whether the request is user-initiated
+		const hasImages = hasCopilotVisionInput(context.messages);
-		// or agent-initiated (e.g. follow-up after assistant/tool messages). If there is
+		const copilotHeaders = buildCopilotDynamicHeaders({
-		// no prior message, default to user-initiated.
+			messages: context.messages,
-		const messages = context.messages || [];
+			hasImages,
-		const lastMessage = messages[messages.length - 1];
-		const isAgentCall = lastMessage ? lastMessage.role !== "user" : false;
-		headers["X-Initiator"] = isAgentCall ? "agent" : "user";
-		headers["Openai-Intent"] = "conversation-edits";
-
-		// Copilot requires this header when sending images
-		const hasImages = messages.some((msg) => {
-			if (msg.role === "user" && Array.isArray(msg.content)) {
-				return msg.content.some((c) => c.type === "image");
-			}
-			if (msg.role === "toolResult" && Array.isArray(msg.content)) {
-				return msg.content.some((c) => c.type === "image");
-			}
-			return false;
 		});
-		if (hasImages) {
+		Object.assign(headers, copilotHeaders);
-			headers["Copilot-Vision-Request"] = "true";
-		}
 	}
 
 	// Merge options headers last so they can override defaults

packages/ai/src/providers/openai-responses.ts

@@ -14,6 +14,7 @@ import type {
 	Usage,
 } from "../types.js";
 import { AssistantMessageEventStream } from "../utils/event-stream.js";
+import { buildCopilotDynamicHeaders, hasCopilotVisionInput } from "./github-copilot-headers.js";
 import { convertResponsesMessages, convertResponsesTools, processResponsesStream } from "./openai-responses-shared.js";
 import { buildBaseOptions, clampReasoning } from "./simple-options.js";
 
@@ -159,28 +160,12 @@ function createClient(
 
 	const headers = { ...model.headers };
 	if (model.provider === "github-copilot") {
-		// Copilot expects X-Initiator to indicate whether the request is user-initiated
+		const hasImages = hasCopilotVisionInput(context.messages);
-		// or agent-initiated (e.g. follow-up after assistant/tool messages). If there is
+		const copilotHeaders = buildCopilotDynamicHeaders({
-		// no prior message, default to user-initiated.
+			messages: context.messages,
-		const messages = context.messages || [];
+			hasImages,
-		const lastMessage = messages[messages.length - 1];
-		const isAgentCall = lastMessage ? lastMessage.role !== "user" : false;
-		headers["X-Initiator"] = isAgentCall ? "agent" : "user";
-		headers["Openai-Intent"] = "conversation-edits";
-
-		// Copilot requires this header when sending images
-		const hasImages = messages.some((msg) => {
-			if (msg.role === "user" && Array.isArray(msg.content)) {
-				return msg.content.some((c) => c.type === "image");
-			}
-			if (msg.role === "toolResult" && Array.isArray(msg.content)) {
-				return msg.content.some((c) => c.type === "image");
-			}
-			return false;
 		});
-		if (hasImages) {
+		Object.assign(headers, copilotHeaders);
-			headers["Copilot-Vision-Request"] = "true";
-		}
 	}
 
 	// Merge options headers last so they can override defaults

packages/ai/test/github-copilot-anthropic-auth.test.ts

@@ -40,7 +40,7 @@ describe("Anthropic Copilot auth config", () => {
 		});
 
 		expect(options.apiKey).toBeNull();
-		expect(options.defaultHeaders?.["Authorization"]).toBe(`Bearer ${token}`);
+		expect(options.defaultHeaders?.Authorization).toBe(`Bearer ${token}`);
 	});
 
 	it("includes Copilot static headers from model.headers", () => {

packages/ai/test/github-copilot-claude-messages-routing.test.ts

@@ -28,7 +28,7 @@ describe("Copilot Claude model routing", () => {
 
 	it("does not have compat block on Claude models (completions-API-specific)", () => {
 		const sonnet = getModel("github-copilot", "claude-sonnet-4");
-		expect((sonnet as any).compat).toBeUndefined();
+		expect("compat" in sonnet).toBe(false);
 	});
 
 	it("preserves static Copilot headers on Claude models", () => {

packages/ai/test/github-copilot-headers.test.ts

@@ -75,6 +75,17 @@ describe("inferCopilotInitiator", () => {
 		];
 		expect(inferCopilotInitiator(messages)).toBe("agent");
 	});
+
+	it("returns 'agent' for any non-user role (e.g. 'tool' in OpenAI format)", () => {
+		const messages: unknown[] = [
+			{
+				role: "tool",
+				tool_call_id: "call_abc123",
+				content: "tool output",
+			},
+		];
+		expect(inferCopilotInitiator(messages)).toBe("agent");
+	});
 });
 
 describe("hasCopilotVisionInput", () => {