diff --git a/astrbot/core/provider/sources/anthropic_source.py b/astrbot/core/provider/sources/anthropic_source.py
index 20a3a813d5..19762282fb 100644
--- a/astrbot/core/provider/sources/anthropic_source.py
+++ b/astrbot/core/provider/sources/anthropic_source.py
@@ -112,11 +112,17 @@ def _init_api_key(self, provider_config: dict) -> None:
         self.chosen_api_key: str = ""
         self.api_keys: list = super().get_keys()
         self.chosen_api_key = self.api_keys[0] if len(self.api_keys) > 0 else ""
+        # SDK 2.x uses Bearer auth; compatible endpoints may require X-Api-Key.
+        default_headers = {"X-Api-Key": self.chosen_api_key}
+        for name, value in (self.custom_headers or {}).items():
+            # Match older SDK casing to avoid duplicate API key headers.
+            name = "X-Api-Key" if name.lower() == "x-api-key" else name
+            default_headers[name] = value
         self.client = AsyncAnthropic(
             api_key=self.chosen_api_key,
             timeout=self.timeout,
             base_url=self.base_url,
-            default_headers=self.custom_headers,
+            default_headers=default_headers,
             http_client=self._create_http_client(provider_config),
         )
 
diff --git a/tests/test_anthropic_kimi_code_provider.py b/tests/test_anthropic_kimi_code_provider.py
index d67fd56fd5..69b7431bb2 100644
--- a/tests/test_anthropic_kimi_code_provider.py
+++ b/tests/test_anthropic_kimi_code_provider.py
@@ -77,6 +77,7 @@ def test_anthropic_provider_passes_custom_headers_via_default_headers(monkeypatc
     assert provider.client.kwargs["default_headers"] == {
         "User-Agent": "custom-agent/1.0",
         "X-Test-Header": "123",
+        "X-Api-Key": "test-key",
     }
     assert provider.client.kwargs["http_client"] is None
 
@@ -103,6 +104,7 @@ def test_kimi_code_provider_sets_defaults_and_preserves_custom_headers(monkeypat
     assert provider.client.kwargs["default_headers"] == {
         "User-Agent": kimi_code_source.KIMI_CODE_USER_AGENT,
         "X-Trace-Id": "trace-1",
+        "X-Api-Key": "test-key",
     }
 
 
diff --git a/tests/test_anthropic_source.py b/tests/test_anthropic_source.py
index 38d059aaad..60f4965382 100644
--- a/tests/test_anthropic_source.py
+++ b/tests/test_anthropic_source.py
@@ -20,6 +20,45 @@ def _provider() -> ProviderAnthropic:
     return ProviderAnthropic.__new__(ProviderAnthropic)
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    ("custom_headers", "expected_key"),
+    [({}, "test-key"), ({"x-api-key": "override-key"}, "override-key")],
+)
+async def test_anthropic_request_sends_single_api_key_header(
+    monkeypatch, custom_headers, expected_key
+):
+    monkeypatch.delenv("ANTHROPIC_AUTH_TOKEN", raising=False)
+    monkeypatch.delenv("ANTHROPIC_CUSTOM_HEADERS", raising=False)
+
+    def handle(request):
+        assert request.headers.get_list("x-api-key") == [expected_key]
+        return sdk_httpx.Response(200, json={})
+
+    async with sdk_httpx.AsyncClient(
+        transport=sdk_httpx.MockTransport(handle)
+    ) as http_client:
+        monkeypatch.setattr(
+            ProviderAnthropic,
+            "_create_http_client",
+            lambda self, config: http_client,
+        )
+        provider = ProviderAnthropic(
+            provider_config={
+                "key": ["test-key"],
+                "api_base": "https://opencode.ai/zen/go",
+                "custom_headers": custom_headers,
+            },
+            provider_settings={},
+        )
+        provider.client.max_retries = 0
+        await provider.client.messages.with_raw_response.create(
+            model="claude-test",
+            max_tokens=16,
+            messages=[{"role": "user", "content": "hi"}],
+        )
+
+
 def test_anthropic_extract_usage_counts_cache_creation_input():
     provider = _provider()