diff --git a/mini_swe_runner.py b/mini_swe_runner.py
index ffa28f769..6a3871d76 100644
--- a/mini_swe_runner.py
+++ b/mini_swe_runner.py
@@ -202,9 +202,10 @@ class MiniSWERunner:
 
         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."
+                "Anthropic's native /v1/messages API is not supported yet (planned for a future release). "
+                "Hermes currently requires OpenAI-compatible /chat/completions endpoints. "
+                "To use Claude models now, route through OpenRouter (OPENROUTER_API_KEY) "
+                "or any OpenAI-compatible proxy that wraps the Anthropic API."
             )
         
         # Handle API key - OpenRouter is the primary provider
diff --git a/run_agent.py b/run_agent.py
index 0bd785bab..d66e4099d 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -185,9 +185,10 @@ class AIAgent:
         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."
+                "Anthropic's native /v1/messages API is not supported yet (planned for a future release). "
+                "Hermes currently requires OpenAI-compatible /chat/completions endpoints. "
+                "To use Claude models now, route through OpenRouter (OPENROUTER_API_KEY) "
+                "or any OpenAI-compatible proxy that wraps the Anthropic API."
             )
         self.tool_progress_callback = tool_progress_callback
         self.clarify_callback = clarify_callback
diff --git a/tests/test_run_agent.py b/tests/test_run_agent.py
index ca53d8af5..2d3703933 100644
--- a/tests/test_run_agent.py
+++ b/tests/test_run_agent.py
@@ -285,7 +285,7 @@ class TestInit:
             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"):
+            with pytest.raises(ValueError, match="not supported yet"):
                 AIAgent(
                     api_key="test-key-1234567890",
                     base_url="https://api.anthropic.com/v1/messages",