diff --git a/agent/anthropic_adapter.py b/agent/anthropic_adapter.py
index 1e6a2a240..2678e85bb 100644
--- a/agent/anthropic_adapter.py
+++ b/agent/anthropic_adapter.py
@@ -328,10 +328,15 @@ def normalize_model_name(model: str) -> str:
     """Normalize a model name for the Anthropic API.
 
     - Strips 'anthropic/' prefix (OpenRouter format, case-insensitive)
+    - Converts dots to hyphens in version numbers (OpenRouter uses dots,
+      Anthropic uses hyphens: claude-opus-4.6 → claude-opus-4-6)
     """
     lower = model.lower()
     if lower.startswith("anthropic/"):
         model = model[len("anthropic/"):]
+    # OpenRouter uses dots for version separators (claude-opus-4.6),
+    # Anthropic uses hyphens (claude-opus-4-6). Convert dots to hyphens.
+    model = model.replace(".", "-")
     return model
 
 
diff --git a/tests/test_anthropic_adapter.py b/tests/test_anthropic_adapter.py
index 1f4006d51..cc563f105 100644
--- a/tests/test_anthropic_adapter.py
+++ b/tests/test_anthropic_adapter.py
@@ -351,6 +351,17 @@ class TestNormalizeModelName:
     def test_leaves_bare_name(self):
         assert normalize_model_name("claude-sonnet-4-20250514") == "claude-sonnet-4-20250514"
 
+    def test_converts_dots_to_hyphens(self):
+        """OpenRouter uses dots (4.6), Anthropic uses hyphens (4-6)."""
+        assert normalize_model_name("anthropic/claude-opus-4.6") == "claude-opus-4-6"
+        assert normalize_model_name("anthropic/claude-sonnet-4.5") == "claude-sonnet-4-5"
+        assert normalize_model_name("claude-opus-4.6") == "claude-opus-4-6"
+
+    def test_already_hyphenated_unchanged(self):
+        """Names already in Anthropic format should pass through."""
+        assert normalize_model_name("claude-opus-4-6") == "claude-opus-4-6"
+        assert normalize_model_name("claude-opus-4-5-20251101") == "claude-opus-4-5-20251101"
+
 
 # ---------------------------------------------------------------------------
 # Tool conversion