From 0c0a2eb0a27923e8a801a19d5c151d8abb27af8d Mon Sep 17 00:00:00 2001
From: adavyas <adavyasharma@gmail.com>
Date: Fri, 27 Feb 2026 21:19:29 -0800
Subject: [PATCH] fix(agent): fail fast on Anthropic native base URLs

---
 mini_swe_runner.py      |  7 +++++++
 run_agent.py            |  6 ++++++
 tests/test_run_agent.py | 17 +++++++++++++++++
 3 files changed, 30 insertions(+)

diff --git a/mini_swe_runner.py b/mini_swe_runner.py
index 3fe0e0162..ffa28f769 100644
--- a/mini_swe_runner.py
+++ b/mini_swe_runner.py
@@ -199,6 +199,13 @@ class MiniSWERunner:
             client_kwargs["base_url"] = base_url
         else:
             client_kwargs["base_url"] = "https://openrouter.ai/api/v1"
+
+        if base_url and "api.anthropic.com" in base_url.strip().lower():
+            raise ValueError(
+                "Anthropic /v1/messages is not supported yet. "
+                "Hermes uses OpenAI-compatible /chat/completions. "
+                "Use OpenRouter or leave base_url unset."
+            )
         
         # Handle API key - OpenRouter is the primary provider
         if api_key:
diff --git a/run_agent.py b/run_agent.py
index 8958353f5..0a539616d 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -183,6 +183,12 @@ class AIAgent:
         # Store effective base URL for feature detection (prompt caching, reasoning, etc.)
         # When no base_url is provided, the client defaults to OpenRouter, so reflect that here.
         self.base_url = base_url or OPENROUTER_BASE_URL
+        if base_url and "api.anthropic.com" in base_url.strip().lower():
+            raise ValueError(
+                "Anthropic /v1/messages is not supported yet. "
+                "Hermes uses OpenAI-compatible /chat/completions. "
+                "Use OpenRouter or leave base_url unset."
+            )
         self.tool_progress_callback = tool_progress_callback
         self.clarify_callback = clarify_callback
         self._last_reported_tool = None  # Track for "new tool" mode
diff --git a/tests/test_run_agent.py b/tests/test_run_agent.py
index a07c52f84..77ef460ab 100644
--- a/tests/test_run_agent.py
+++ b/tests/test_run_agent.py
@@ -278,6 +278,23 @@ class TestMaskApiKey:
 
 
 class TestInit:
+    def test_anthropic_base_url_fails_fast(self):
+        """Anthropic native endpoints should error before building an OpenAI client."""
+        with (
+            patch("run_agent.get_tool_definitions", return_value=[]),
+            patch("run_agent.check_toolset_requirements", return_value={}),
+            patch("run_agent.OpenAI") as mock_openai,
+        ):
+            with pytest.raises(ValueError, match="Anthropic /v1/messages is not supported yet"):
+                AIAgent(
+                    api_key="test-key-1234567890",
+                    base_url="https://api.anthropic.com/v1/messages",
+                    quiet_mode=True,
+                    skip_context_files=True,
+                    skip_memory=True,
+                )
+            mock_openai.assert_not_called()
+
     def test_prompt_caching_claude_openrouter(self):
         """Claude model via OpenRouter should enable prompt caching."""
         with (