diff --git a/AGENTS.md b/AGENTS.md
index 99ee047..c0d4306 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -123,3 +123,4 @@ Query params configure `PageAgentConfig` in `src/umd.ts`.
 
 - Explicit typing for exported/public APIs
 - ESLint relaxes some unsafe rules for rapid iteration
+- All code and comments must be in English.
diff --git a/packages/llms/src/OpenAILenientClient.ts b/packages/llms/src/OpenAILenientClient.ts
index 64c723d..b35f3f1 100644
--- a/packages/llms/src/OpenAILenientClient.ts
+++ b/packages/llms/src/OpenAILenientClient.ts
@@ -6,10 +6,12 @@ import type { InvokeResult, LLMClient, LLMConfig, MacroToolInput, Message, Tool
 import { lenientParseMacroToolCall, modelPatch, zodToOpenAITool } from './utils'
 
 export class OpenAIClient implements LLMClient {
-	config: LLMConfig
+	config: Required<LLMConfig>
+	private fetch: typeof globalThis.fetch
 
-	constructor(config: LLMConfig) {
+	constructor(config: Required<LLMConfig>) {
 		this.config = config
+		this.fetch = config.customFetch
 	}
 
 	async invoke(
@@ -23,7 +25,7 @@ export class OpenAIClient implements LLMClient {
 		// 2. Call API
 		let response: Response
 		try {
-			response = await fetch(`${this.config.baseURL}/chat/completions`, {
+			response = await this.fetch(`${this.config.baseURL}/chat/completions`, {
 				method: 'POST',
 				headers: {
 					'Content-Type': 'application/json',
diff --git a/packages/llms/src/index.ts b/packages/llms/src/index.ts
index 644b308..38f2527 100644
--- a/packages/llms/src/index.ts
+++ b/packages/llms/src/index.ts
@@ -71,6 +71,7 @@ export function parseLLMConfig(config: LLMConfig): Required<LLMConfig> {
 		temperature: config.temperature ?? DEFAULT_TEMPERATURE,
 		maxTokens: config.maxTokens ?? DEFAULT_MAX_TOKENS,
 		maxRetries: config.maxRetries ?? LLM_MAX_RETRIES,
+		customFetch: config.customFetch ?? globalThis.fetch,
 	}
 }
 
@@ -83,13 +84,7 @@ export class LLM extends EventTarget {
 		this.config = parseLLMConfig(config)
 
 		// Default to OpenAI client
-		this.client = new OpenAIClient({
-			model: this.config.model,
-			apiKey: this.config.apiKey,
-			baseURL: this.config.baseURL,
-			temperature: this.config.temperature,
-			maxTokens: this.config.maxTokens,
-		})
+		this.client = new OpenAIClient(this.config)
 	}
 
 	/**
diff --git a/packages/llms/src/types.ts b/packages/llms/src/types.ts
index d978417..10e547c 100644
--- a/packages/llms/src/types.ts
+++ b/packages/llms/src/types.ts
@@ -71,9 +71,17 @@ export interface LLMConfig {
 	baseURL?: string
 	apiKey?: string
 	model?: string
+
 	temperature?: number
 	maxTokens?: number
 	maxRetries?: number
+
+	/**
+	 * Custom fetch function for LLM API requests.
+	 * Use this to customize headers, credentials, proxy, etc.
+	 * The response should follow OpenAI API format.
+	 */
+	customFetch?: typeof globalThis.fetch
 }
 
 /**
diff --git a/packages/website/src/docs/integration/configuration/page.tsx b/packages/website/src/docs/integration/configuration/page.tsx
index 1af83a9..9b6ef44 100644
--- a/packages/website/src/docs/integration/configuration/page.tsx
+++ b/packages/website/src/docs/integration/configuration/page.tsx
@@ -18,6 +18,13 @@ interface LLMConfig {
 	temperature?: number
 	maxTokens?: number
 	maxRetries?: number
+
+	/**
+	 * Custom fetch function for LLM API requests.
+	 * Use this to customize headers, credentials, proxy, etc.
+	 * The response should follow OpenAI API format.
+	 */
+	customFetch?: typeof globalThis.fetch
 }
 
 interface AgentConfig {