diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 39daa4deed..0c8253d3e5 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -1283,7 +1283,7 @@ def _to_openai_base_url(base_url: str) -> str:
         # ZAI uses /api/anthropic for the Coding Plan's Anthropic wire.  The
         # matching OpenAI-wire endpoint is /api/coding/paas/v4; /api/paas/v4
         # is the independently billed general API.
-        if "open.bigmodel.cn" in url or "bigmodel" in url or "api.z.ai" in url:
+        if base_url_host_matches(url, "open.bigmodel.cn") or base_url_host_matches(url, "api.z.ai"):
             rewritten = url[: -len("/anthropic")] + "/coding/paas/v4"
             logger.debug("Auxiliary client: rewrote ZAI base URL %s → %s", url, rewritten)
             return rewritten
@@ -1297,7 +1297,7 @@ def _to_openai_base_url(base_url: str) -> str:
             url,
         )
         return url
-    if "api.kimi.com" in url and url.endswith("/coding"):
+    if base_url_host_matches(url, "api.kimi.com") and url.endswith("/coding"):
         # Kimi Code uses /coding/v1/messages for Anthropic SDK (appends /v1/messages)
         # but /coding/v1/chat/completions for OpenAI SDK (appends /chat/completions)
         # Without /v1 here, OpenAI SDK hits /coding/chat/completions — a 404.
diff --git a/tests/agent/test_minimax_auxiliary_url.py b/tests/agent/test_minimax_auxiliary_url.py
index 0f07670c7c..bfc41a0002 100644
--- a/tests/agent/test_minimax_auxiliary_url.py
+++ b/tests/agent/test_minimax_auxiliary_url.py
@@ -51,5 +51,24 @@ class TestToOpenaiBaseUrl:
             == "https://open.bigmodel.cn/api/coding/paas/v4"
         )
 
+    def test_bigmodel_marker_in_path_does_not_false_positive(self):
+        """Host-anchored matching: 'bigmodel' in the path must not trigger rewrite."""
+        url = "https://gateway.example.com/proxy/bigmodel-fallback/anthropic"
+        assert _to_openai_base_url(url) == url
+
+    def test_zai_marker_in_path_does_not_false_positive(self):
+        url = "https://gateway.example.com/api.z.ai-mirror/anthropic"
+        assert _to_openai_base_url(url) == url
+
+    def test_kimi_coding_host_rewritten(self):
+        assert (
+            _to_openai_base_url("https://api.kimi.com/coding")
+            == "https://api.kimi.com/coding/v1"
+        )
+
+    def test_kimi_marker_in_path_does_not_false_positive(self):
+        url = "https://gateway.example.com/some/api.kimi.com-proxy/coding"
+        assert _to_openai_base_url(url) == url
+
     def test_none(self):
         assert _to_openai_base_url(None) == ""