diff --git a/src/models/__tests__/openai.test.ts b/src/models/__tests__/openai.test.ts
index 01614b7f..9419fd1a 100644
--- a/src/models/__tests__/openai.test.ts
+++ b/src/models/__tests__/openai.test.ts
@@ -100,7 +100,7 @@ describe('OpenAIModel', () => {
         vi.stubEnv('OPENAI_API_KEY', '')
       }
       expect(() => new OpenAIModel({ modelId: 'gpt-4o' })).toThrow(
-        "OpenAI API key is required. Provide it via the 'apiKey' option or set the OPENAI_API_KEY environment variable."
+        "OpenAI API key is required. Provide it via the 'apiKey' option (string or function) or set the OPENAI_API_KEY environment variable."
       )
     })
 
@@ -144,6 +144,37 @@ describe('OpenAIModel', () => {
       const mockClient = {} as OpenAI
       expect(() => new OpenAIModel({ modelId: 'gpt-4o', client: mockClient })).not.toThrow()
     })
+
+    it('accepts function-based API key', () => {
+      const apiKeyFn = vi.fn(async () => 'sk-dynamic')
+      new OpenAIModel({
+        modelId: 'gpt-4o',
+        apiKey: apiKeyFn,
+      })
+      expect(OpenAI).toHaveBeenCalledWith(
+        expect.objectContaining({
+          apiKey: apiKeyFn,
+        })
+      )
+    })
+
+    it('accepts async function-based API key', () => {
+      const apiKeyFn = async (): Promise<string> => {
+        await new Promise((resolve) => globalThis.setTimeout(resolve, 10))
+        return 'sk-async-key'
+      }
+
+      new OpenAIModel({
+        modelId: 'gpt-4o',
+        apiKey: apiKeyFn,
+      })
+
+      expect(OpenAI).toHaveBeenCalledWith(
+        expect.objectContaining({
+          apiKey: apiKeyFn,
+        })
+      )
+    })
   })
 
   describe('updateConfig', () => {
diff --git a/src/models/openai.ts b/src/models/openai.ts
index 3e325a22..85d3a18b 100644
--- a/src/models/openai.ts
+++ b/src/models/openai.ts
@@ -8,6 +8,7 @@
  */
 
 import OpenAI, { type ClientOptions } from 'openai'
+import type { ApiKeySetter } from 'openai/client'
 import { Model } from '../models/model.js'
 import type { BaseModelConfig, StreamOptions } from '../models/model.js'
 import type { Message } from '../types/messages.js'
@@ -169,8 +170,12 @@ export interface OpenAIModelConfig extends BaseModelConfig {
 export interface OpenAIModelOptions extends OpenAIModelConfig {
   /**
    * OpenAI API key (falls back to OPENAI_API_KEY environment variable).
+   *
+   * Accepts either a static string or an async function that resolves to a string.
+   * When a function is provided, it is invoked before each request, allowing for
+   * dynamic API key rotation or runtime credential refresh.
    */
-  apiKey?: string
+  apiKey?: string | ApiKeySetter
 
   /**
    * Pre-configured OpenAI client instance.
@@ -241,6 +246,12 @@ export class OpenAIModel extends Model<OpenAIModelConfig> {
    *   modelId: 'gpt-3.5-turbo'
    * })
    *
+   * // Using function-based API key for dynamic key retrieval
+   * const provider = new OpenAIModel({
+   *   modelId: 'gpt-4o',
+   *   apiKey: async () => await getRotatingApiKey()
+   * })
+   *
    * // Using a pre-configured client instance
    * const client = new OpenAI({ apiKey: 'sk-...', timeout: 60000 })
    * const provider = new OpenAIModel({
@@ -267,7 +278,7 @@ export class OpenAIModel extends Model<OpenAIModelConfig> {
         typeof process !== 'undefined' && typeof process.env !== 'undefined' && process.env.OPENAI_API_KEY
       if (!apiKey && !hasEnvKey) {
         throw new Error(
-          "OpenAI API key is required. Provide it via the 'apiKey' option or set the OPENAI_API_KEY environment variable."
+          "OpenAI API key is required. Provide it via the 'apiKey' option (string or function) or set the OPENAI_API_KEY environment variable."
         )
       }