diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index 63a3704d8..48f0d34ba 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "5.19.0"
+  ".": "5.19.1"
 }
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ddbf18dd..d9b8e7d29 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 5.19.1 (2025-09-03)
+
+Full Changelog: [v5.19.0...v5.19.1](https://github.com/openai/openai-node/compare/v5.19.0...v5.19.1)
+
+### Bug Fixes
+
+* **azure:** correctly send API key ([#1635](https://github.com/openai/openai-node/issues/1635)) ([08f6178](https://github.com/openai/openai-node/commit/08f6178ff0d4ccc6b80462c86a36f11eb3bfd5fe))
+
 ## 5.19.0 (2025-09-03)
 
 Full Changelog: [v5.18.1...v5.19.0](https://github.com/openai/openai-node/compare/v5.18.1...v5.19.0)
diff --git a/jsr.json b/jsr.json
index 968472c49..d6d3f55a9 100644
--- a/jsr.json
+++ b/jsr.json
@@ -1,6 +1,6 @@
 {
   "name": "@openai/openai",
-  "version": "5.19.0",
+  "version": "5.19.1",
   "exports": {
     ".": "./index.ts",
     "./helpers/zod": "./helpers/zod.ts",
diff --git a/package.json b/package.json
index 7f78591e8..a8fd383fc 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "openai",
-  "version": "5.19.0",
+  "version": "5.19.1",
   "description": "The official TypeScript library for the OpenAI API",
   "author": "OpenAI <support@openai.com>",
   "types": "dist/index.d.ts",
diff --git a/src/azure.ts b/src/azure.ts
index 5719fc40c..97765df6d 100644
--- a/src/azure.ts
+++ b/src/azure.ts
@@ -1,4 +1,6 @@
 import type { RequestInit } from './internal/builtin-types';
+import type { NullableHeaders } from './internal/headers';
+import { buildHeaders } from './internal/headers';
 import * as Errors from './error';
 import { FinalRequestOptions } from './internal/request-options';
 import { isObj, readEnv } from './internal/utils';
@@ -134,6 +136,13 @@ export class AzureOpenAI extends OpenAI {
     }
     return super.buildRequest(options, props);
   }
+
+  protected override async authHeaders(opts: FinalRequestOptions): Promise<NullableHeaders | undefined> {
+    if (typeof this._options.apiKey === 'string') {
+      return buildHeaders([{ 'api-key': this.apiKey }]);
+    }
+    return super.authHeaders(opts);
+  }
 }
 
 const _deployments_endpoints = new Set([
diff --git a/src/client.ts b/src/client.ts
index cc2cc0a30..b3c899b44 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -331,7 +331,7 @@ export class OpenAI {
   private fetch: Fetch;
   #encoder: Opts.RequestEncoder;
   protected idempotencyHeader?: string;
-  private _options: ClientOptions;
+  protected _options: ClientOptions;
 
   /**
    * API Client for interfacing with the OpenAI API.
diff --git a/src/version.ts b/src/version.ts
index 6bd23c18e..51eae91f3 100644
--- a/src/version.ts
+++ b/src/version.ts
@@ -1 +1 @@
-export const VERSION = '5.19.0'; // x-release-please-version
+export const VERSION = '5.19.1'; // x-release-please-version
diff --git a/tests/lib/azure.test.ts b/tests/lib/azure.test.ts
index b93defab0..82af3ec85 100644
--- a/tests/lib/azure.test.ts
+++ b/tests/lib/azure.test.ts
@@ -307,6 +307,22 @@ describe('instantiate azure client', () => {
     });
   });
 
+  test('uses api-key header when apiKey is provided', async () => {
+    const testFetch = async (url: RequestInfo, { headers }: RequestInit = {}): Promise<Response> => {
+      return new Response(JSON.stringify({ a: 1 }), { headers: headers ?? [] });
+    };
+    const client = new AzureOpenAI({
+      baseURL: 'http://localhost:5000/',
+      apiKey: 'My API Key',
+      apiVersion,
+      fetch: testFetch,
+    });
+
+    const res = await client.request({ method: 'post', path: 'https://example.com' }).asResponse();
+    expect(res.headers.get('api-key')).toEqual('My API Key');
+    expect(res.headers.get('authorization')).toEqual(null);
+  });
+
   test('with endpoint', () => {
     const client = new AzureOpenAI({ endpoint: 'https://example.com', apiKey: 'My API Key', apiVersion });
     expect(client.baseURL).toEqual('https://example.com/openai');