From 6ec1263e9faf6c3baa83a4bfb0972ca7be267f9c Mon Sep 17 00:00:00 2001
From: Anubhav <anubhavlal.15@gmail.com>
Date: Mon, 9 Nov 2026 22:36:15 +0530
Subject: [PATCH] fix(client): send additional_headers from async_api

---
 langfuse/_client/resource_manager.py         |  1 +
 tests/unit/test_additional_headers_simple.py | 25 ++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/langfuse/_client/resource_manager.py b/langfuse/_client/resource_manager.py
index 1c1afa424..360fc7d5d 100644
--- a/langfuse/_client/resource_manager.py
+++ b/langfuse/_client/resource_manager.py
@@ -366,6 +366,7 @@ def _init_api_clients(self) -> None:
             x_langfuse_sdk_name="python",
             x_langfuse_sdk_version=langfuse_version,
             x_langfuse_public_key=self.public_key,
+            headers=self.additional_headers,
             timeout=self.timeout,
         )
 
diff --git a/tests/unit/test_additional_headers_simple.py b/tests/unit/test_additional_headers_simple.py
index d05475a3c..e22c4c141 100644
--- a/tests/unit/test_additional_headers_simple.py
+++ b/tests/unit/test_additional_headers_simple.py
@@ -3,6 +3,7 @@
 This module tests that additional headers are properly configured in the HTTP clients.
 """
 
+import asyncio
 from typing import Sequence
 
 import httpx
@@ -56,6 +57,30 @@ def test_httpx_client_has_additional_headers_when_none_provided(self):
             == "another-value"
         )
 
+    def test_async_api_sends_additional_headers(self):
+        langfuse = Langfuse(
+            public_key="test-public-key",
+            secret_key="test-secret-key",
+            host="https://mock-host.com",
+            additional_headers={"X-Custom-Header": "custom-value"},
+            tracing_enabled=False,
+        )
+        captured_requests = []
+
+        def handler(request: httpx.Request) -> httpx.Response:
+            captured_requests.append(request)
+            return httpx.Response(200, json={"status": "OK", "version": "1.0.0"})
+
+        wrapper = langfuse.async_api._client_wrapper
+        wrapper.httpx_client.httpx_client = httpx.AsyncClient(
+            transport=httpx.MockTransport(handler)
+        )
+
+        asyncio.run(langfuse.async_api.health.health())
+
+        assert len(captured_requests) == 1
+        assert captured_requests[0].headers["X-Custom-Header"] == "custom-value"
+
     def test_custom_httpx_client_with_additional_headers_ignores_additional_headers(
         self,
     ):