diff --git a/apps/backend/core/providers/config.py b/apps/backend/core/providers/config.py
index 386fe5566..de0be683d 100644
--- a/apps/backend/core/providers/config.py
+++ b/apps/backend/core/providers/config.py
@@ -372,6 +372,25 @@ def get_model_for(self, provider: str) -> str | None:
             return self.ollama_model or None
         return None
 
+    def coherent_session_model(self, requested_model: str | None) -> str | None:
+        """Return a model id coherent with this config's provider.
+
+        The phase-model default is Claude-centric (``phase_config`` tiers
+        resolve to ``claude-*`` ids). When the configured provider is a
+        non-Claude provider and ``requested_model`` is a Claude-family id,
+        return the provider's OWN configured model instead, so a direct-API
+        session does not receive a Claude id it cannot serve (404
+        model_not_found). Otherwise return ``requested_model`` unchanged.
+
+        This is the QA-path analog of the coder fix in #337; both keep a
+        Claude-family phase default from leaking into a non-Claude session.
+        """
+        if self.provider != "claude" and (requested_model or "").startswith("claude"):
+            provider_model = self.get_model_for(self.provider)
+            if provider_model:
+                return provider_model
+        return requested_model
+
     def with_provider_model(self, provider: str, model: str) -> "ProviderConfig":
         """Return a copy configured to use the given provider/model pair."""
         provider = provider.lower()
diff --git a/apps/backend/qa/fixer.py b/apps/backend/qa/fixer.py
index 84f6c1651..d32f9ddbf 100644
--- a/apps/backend/qa/fixer.py
+++ b/apps/backend/qa/fixer.py
@@ -212,10 +212,12 @@ def _build_qa_fixer_runtime_session(
             f"routed={provider_name}, env={config.provider}"
         )
     provider = create_engine_provider(config)
+    # Keep a Claude-family QA phase default from 404ing a direct provider
+    # (the QA-path analog of #337). See ProviderConfig.coherent_session_model.
     session = provider.create_session(
         SessionConfig(
             name=f"qa_fixer-runtime-{fix_session}",
-            model=model,
+            model=config.coherent_session_model(model),
             extra={"agent_type": "qa_fixer"},
         )
     )
diff --git a/apps/backend/qa/reviewer.py b/apps/backend/qa/reviewer.py
index 12a858eb9..04cff5eca 100644
--- a/apps/backend/qa/reviewer.py
+++ b/apps/backend/qa/reviewer.py
@@ -579,10 +579,12 @@ async def run_qa_reviewer_runtime_session(
             f"routed={provider_name}, env={config.provider}"
         )
     provider = create_engine_provider(config)
+    # Keep a Claude-family QA phase default from 404ing a direct provider
+    # (the QA-path analog of #337). See ProviderConfig.coherent_session_model.
     session = provider.create_session(
         SessionConfig(
             name=f"qa_reviewer-runtime-{qa_session}",
-            model=model,
+            model=config.coherent_session_model(model),
             extra={"agent_type": "qa_reviewer"},
         )
     )
diff --git a/tests/test_provider_coherent_model.py b/tests/test_provider_coherent_model.py
new file mode 100644
index 000000000..26b0e9d84
--- /dev/null
+++ b/tests/test_provider_coherent_model.py
@@ -0,0 +1,47 @@
+"""Tests for ProviderConfig.coherent_session_model (QA/coder model coherence)."""
+
+from core.providers.config import ProviderConfig
+
+
+def test_claude_family_model_replaced_for_direct_provider():
+    """A claude-family phase default must not reach a non-Claude session."""
+    config = ProviderConfig(provider="openai", openai_model="gpt-5.2")
+
+    assert (
+        config.coherent_session_model("claude-sonnet-4-5-20250929") == "gpt-5.2"
+    )
+
+
+def test_explicit_provider_model_is_preserved():
+    config = ProviderConfig(provider="openai", openai_model="gpt-5.2")
+
+    assert config.coherent_session_model("gpt-4o") == "gpt-4o"
+
+
+def test_none_model_passes_through():
+    config = ProviderConfig(provider="openai", openai_model="gpt-5.2")
+
+    assert config.coherent_session_model(None) is None
+
+
+def test_claude_provider_keeps_claude_model():
+    config = ProviderConfig(
+        provider="claude", claude_model="claude-sonnet-4-5-20250929"
+    )
+
+    assert (
+        config.coherent_session_model("claude-sonnet-4-5-20250929")
+        == "claude-sonnet-4-5-20250929"
+    )
+
+
+def test_direct_provider_without_configured_model_keeps_request():
+    """If the provider has no configured model, fall back to the request
+    rather than returning an empty string."""
+    config = ProviderConfig(provider="openrouter", openrouter_model="")
+
+    # openrouter_model empty -> get_model_for returns "" (falsy) -> keep request
+    assert (
+        config.coherent_session_model("claude-sonnet-4-5-20250929")
+        == "claude-sonnet-4-5-20250929"
+    )