Add custom headers support for models.json

Fixes #39

- Added headers field to Model type (provider and model level)
- Model headers override provider headers when merged
- Supported in all APIs:
  - Anthropic: defaultHeaders
  - OpenAI (completions/responses): defaultHeaders
  - Google: httpOptions.headers
- Enables bypassing Cloudflare bot detection for proxied endpoints
- Updated documentation with examples

Also fixed:
- Mistral/Chutes syntax error (iif -> if)
- process.env.ANTHROPIC_API_KEY bug (use delete instead of = undefined)

packages/ai/README.md

@@ -576,6 +576,24 @@ const ollamaModel: Model<'openai-completions'> = {
   maxTokens: 32000
 };
 
+// Example: Custom endpoint with headers (bypassing Cloudflare bot detection)
+const proxyModel: Model<'anthropic-messages'> = {
+  id: 'claude-sonnet-4',
+  name: 'Claude Sonnet 4 (Proxied)',
+  api: 'anthropic-messages',
+  provider: 'custom-proxy',
+  baseUrl: 'https://proxy.example.com/v1',
+  reasoning: true,
+  input: ['text', 'image'],
+  cost: { input: 3, output: 15, cacheRead: 0.3, cacheWrite: 3.75 },
+  contextWindow: 200000,
+  maxTokens: 8192,
+  headers: {
+    'User-Agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36',
+    'X-Custom-Auth': 'bearer-token-here'
+  }
+};
+
 // Use the custom model
 const response = await stream(ollamaModel, context, {
   apiKey: 'dummy' // Ollama doesn't need a real key

packages/ai/src/providers/anthropic.ts

@@ -288,11 +288,12 @@ function createClient(
 			accept: "application/json",
 			"anthropic-dangerous-direct-browser-access": "true",
 			"anthropic-beta": "oauth-2025-04-20,fine-grained-tool-streaming-2025-05-14",
+			...(model.headers || {}),
 		};
 
 		// Clear the env var if we're in Node.js to prevent SDK from using it
 		if (typeof process !== "undefined" && process.env) {
-			process.env.ANTHROPIC_API_KEY = undefined;
+			delete process.env.ANTHROPIC_API_KEY;
 		}
 
 		const client = new Anthropic({
@@ -309,6 +310,7 @@ function createClient(
 			accept: "application/json",
 			"anthropic-dangerous-direct-browser-access": "true",
 			"anthropic-beta": "fine-grained-tool-streaming-2025-05-14",
+			...(model.headers || {}),
 		};
 
 		const client = new Anthropic({

packages/ai/src/providers/google.ts

@@ -63,7 +63,7 @@ export const streamGoogle: StreamFunction<"google-generative-ai"> = (
 		};
 
 		try {
-			const client = createClient(options?.apiKey);
+			const client = createClient(model, options?.apiKey);
 			const params = buildParams(model, context, options);
 			const googleStream = await client.models.generateContentStream(params);
 
@@ -252,7 +252,7 @@ export const streamGoogle: StreamFunction<"google-generative-ai"> = (
 	return stream;
 };
 
-function createClient(apiKey?: string): GoogleGenAI {
+function createClient(model: Model<"google-generative-ai">, apiKey?: string): GoogleGenAI {
 	if (!apiKey) {
 		if (!process.env.GEMINI_API_KEY) {
 			throw new Error(
@@ -261,7 +261,10 @@ function createClient(apiKey?: string): GoogleGenAI {
 		}
 		apiKey = process.env.GEMINI_API_KEY;
 	}
-	return new GoogleGenAI({ apiKey });
+	return new GoogleGenAI({
+		apiKey,
+		httpOptions: model.headers ? { headers: model.headers } : undefined,
+	});
 }
 
 function buildParams(

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

@@ -260,7 +260,12 @@ function createClient(model: Model<"openai-completions">, apiKey?: string) {
 		}
 		apiKey = process.env.OPENAI_API_KEY;
 	}
-	return new OpenAI({ apiKey, baseURL: model.baseUrl, dangerouslyAllowBrowser: true });
+	return new OpenAI({
+		apiKey,
+		baseURL: model.baseUrl,
+		dangerouslyAllowBrowser: true,
+		defaultHeaders: model.headers,
+	});
 }
 
 function buildParams(model: Model<"openai-completions">, context: Context, options?: OpenAICompletionsOptions) {
@@ -285,7 +290,7 @@ function buildParams(model: Model<"openai-completions">, context: Context, optio
 
 	if (options?.maxTokens) {
 		// Mistral/Chutes uses max_tokens instead of max_completion_tokens
-		iif (model.baseUrl.includes("mistral.ai") || model.baseUrl.includes("chutes.ai")) {
+		if (model.baseUrl.includes("mistral.ai") || model.baseUrl.includes("chutes.ai")) {
 			(params as any).max_tokens = options?.maxTokens;
 		} else {
 			params.max_completion_tokens = options?.maxTokens;

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

@@ -307,7 +307,12 @@ function createClient(model: Model<"openai-responses">, apiKey?: string) {
 		}
 		apiKey = process.env.OPENAI_API_KEY;
 	}
-	return new OpenAI({ apiKey, baseURL: model.baseUrl, dangerouslyAllowBrowser: true });
+	return new OpenAI({
+		apiKey,
+		baseURL: model.baseUrl,
+		dangerouslyAllowBrowser: true,
+		defaultHeaders: model.headers,
+	});
 }
 
 function buildParams(model: Model<"openai-responses">, context: Context, options?: OpenAIResponsesOptions) {

packages/ai/src/types.ts

@@ -168,4 +168,5 @@ export interface Model<TApi extends Api> {
 	};
 	contextWindow: number;
 	maxTokens: number;
+	headers?: Record<string, string>;
 }