diff --git a/llm_connect/openrouter.py b/llm_connect/openrouter.py
index 9a7c283..623c5a8 100644
--- a/llm_connect/openrouter.py
+++ b/llm_connect/openrouter.py
@@ -37,6 +37,14 @@ class OpenRouterAdapter(LLMAdapter):
         max_retries: Optional[int] = None,
     ):
         self._config = config or LLMConfig()
+        # Track whether the model was explicitly supplied (constructor or
+        # LLMConfig). Comparing self._model to _DEFAULT_MODEL is not enough —
+        # callers who pass --model anthropic/claude-sonnet-4 happen to match
+        # the default and would otherwise be misrouted to RunConfig.model_name
+        # (which defaults to "gpt-4" — quietly sending every call to OpenAI's
+        # gpt-4 model, which is what broke the activity-core CUST-WP-0045
+        # canary on 2026-06-02).
+        self._explicit_model = model is not None or self._config.model is not None
         self._model = model or self._config.model or _DEFAULT_MODEL
         self._api_base = (api_base or self._config.api_base).rstrip("/")
         self._system_prompt = system_prompt
@@ -56,7 +64,14 @@ class OpenRouterAdapter(LLMAdapter):
 
     def execute_prompt(self, prompt: str, config: RunConfig) -> LLMResponse:
         self._preflight_budget(config)
-        model = self._model if self._model != _DEFAULT_MODEL else (config.model_name or self._model)
+        # Explicit constructor/LLMConfig model wins; only fall back to the
+        # per-call RunConfig.model_name when the adapter wasn't told what to
+        # use. RunConfig.model_name defaults to "gpt-4", so falling back
+        # unconditionally would silently misroute callers.
+        if self._explicit_model:
+            model = self._model
+        else:
+            model = config.model_name or self._model
 
         messages: list[Dict[str, str]] = []
         if self._system_prompt: