fix(bedrock): Fable reports 128K context — add Fable + Claude 4.6/4.7/4.8 1M entries to Bedrock table, invalidate stale cache

agent/bedrock_adapter.py

@@ -1276,9 +1276,19 @@ def classify_bedrock_error(error_message: str) -> str:
 # detection is unavailable.
 
 BEDROCK_CONTEXT_LENGTHS: Dict[str, int] = {
-    # Anthropic Claude models on Bedrock
-    "anthropic.claude-opus-4-6":     200_000,
-    "anthropic.claude-sonnet-4-6":   200_000,
+    # Anthropic Claude models on Bedrock.
+    # AWS and Anthropic list Opus/Sonnet 4.6+ as 1M-context Bedrock models;
+    # this fallback must not assume the older Claude-wide 200K window.
+    # These 1M entries must match agent/model_metadata.py DEFAULT_CONTEXT_LENGTHS
+    # or the agent compresses context prematurely (~200K) on a 1M-capable model.
+    # Longest-substring matching means more specific keys (…opus-4-8) win over
+    # the generic …opus-4 fallback, so list the generic 200K entry last.
+    "anthropic.claude-fable-5":      1_000_000,
+    "anthropic.claude-fable":        1_000_000,
+    "anthropic.claude-opus-4-8":     1_000_000,
+    "anthropic.claude-opus-4-7":     1_000_000,
+    "anthropic.claude-opus-4-6":     1_000_000,
+    "anthropic.claude-sonnet-4-6":   1_000_000,
     "anthropic.claude-sonnet-4-5":   200_000,
     "anthropic.claude-haiku-4-5":    200_000,
     "anthropic.claude-opus-4":       200_000,

agent/model_metadata.py

@@ -1584,6 +1584,12 @@ def get_model_context_length(
     # local servers actually know about.  Ollama "model:tag" colons are preserved.
     model = _strip_provider_prefix(model)
 
+    is_bedrock_context = provider == "bedrock" or (
+        base_url
+        and base_url_hostname(base_url).startswith("bedrock-runtime.")
+        and base_url_host_matches(base_url, "amazonaws.com")
+    )
+
     # 1. Check persistent cache (model+provider)
     # LM Studio is excluded — its loaded context length is transient (the
     # user can reload the model with a different context_length at any time
@@ -1652,23 +1658,39 @@ def get_model_context_length(
                     model, base_url,
                 )
                 # Fall through; step 5b reconciles and overwrites if portal responds.
+            # Invalidate stale Bedrock entries seeded before the Claude 4.6+
+            # long-context table was corrected to 1M.
+            elif is_bedrock_context:
+                try:
+                    from agent.bedrock_adapter import get_bedrock_context_length
+                    bedrock_ctx = get_bedrock_context_length(model)
+                    if cached != bedrock_ctx:
+                        logger.info(
+                            "Dropping stale Bedrock cache entry %s@%s -> %s; "
+                            "using static Bedrock table value %s",
+                            model,
+                            base_url,
+                            f"{cached:,}",
+                            f"{bedrock_ctx:,}",
+                        )
+                        _invalidate_cached_context_length(model, base_url)
+                        return bedrock_ctx
+                except ImportError:
+                    pass
+                return cached
             else:
                 return cached
 
     # 1b. AWS Bedrock — use static context length table.
     # Bedrock's ListFoundationModels API doesn't expose context window sizes,
     # so we maintain a curated table in bedrock_adapter.py that reflects
-    # AWS-imposed limits (e.g. 200K for Claude models vs 1M on the native
-    # Anthropic API).  This must run BEFORE the custom-endpoint probe at
+    # Bedrock-hosted model limits (e.g. older Claude 4 at 200K; Claude
+    # Opus/Sonnet 4.6+ at 1M).  This must run BEFORE the custom-endpoint probe at
     # step 2 — bedrock-runtime.<region>.amazonaws.com is not in
     # _URL_TO_PROVIDER, so it would otherwise be treated as a custom endpoint,
     # fail the /models probe (Bedrock doesn't expose that shape), and fall
     # back to the 128K default before reaching the original step 4b branch.
-    if provider == "bedrock" or (
-        base_url
-        and base_url_hostname(base_url).startswith("bedrock-runtime.")
-        and base_url_host_matches(base_url, "amazonaws.com")
-    ):
+    if is_bedrock_context:
         try:
             from agent.bedrock_adapter import get_bedrock_context_length
             return get_bedrock_context_length(model)

tests/agent/test_bedrock_adapter.py

@@ -1099,11 +1099,36 @@ class TestBedrockContextLength:
 
     def test_claude_opus_4_6(self):
         from agent.bedrock_adapter import get_bedrock_context_length
-        assert get_bedrock_context_length("anthropic.claude-opus-4-6-20250514-v1:0") == 200_000
+        # Opus 4.6 is a 1M-context model on Bedrock.
+        assert get_bedrock_context_length("anthropic.claude-opus-4-6-20250514-v1:0") == 1_000_000
+
+    def test_claude_opus_4_7_and_4_8(self):
+        from agent.bedrock_adapter import get_bedrock_context_length
+        # Opus 4.7/4.8 inference profiles must not fall back to the generic
+        # …opus-4 (200K) key.
+        assert get_bedrock_context_length("us.anthropic.claude-opus-4-7") == 1_000_000
+        assert get_bedrock_context_length("us.anthropic.claude-opus-4-8") == 1_000_000
+        assert get_bedrock_context_length("global.anthropic.claude-opus-4-8") == 1_000_000
+
+    def test_claude_fable_5(self):
+        from agent.bedrock_adapter import get_bedrock_context_length
+        # Fable is a 1M-context model. DEFAULT_CONTEXT_LENGTHS already maps
+        # claude-fable-5 -> 1M, but the Bedrock resolution path short-circuits
+        # to this table before consulting it, so without entries here every
+        # Fable inference profile fell through to
+        # BEDROCK_DEFAULT_CONTEXT_LENGTH (128K).
+        assert get_bedrock_context_length("us.anthropic.claude-fable-5") == 1_000_000
+        assert get_bedrock_context_length("global.anthropic.claude-fable-5") == 1_000_000
+        assert get_bedrock_context_length("anthropic.claude-fable-5-v1:0") == 1_000_000
+
+    def test_claude_opus_4_base_stays_200k(self):
+        from agent.bedrock_adapter import get_bedrock_context_length
+        # The original Opus 4 (no minor version) keeps the 200K window.
+        assert get_bedrock_context_length("anthropic.claude-opus-4-20250514-v1:0") == 200_000
 
     def test_claude_sonnet_versioned(self):
         from agent.bedrock_adapter import get_bedrock_context_length
-        assert get_bedrock_context_length("anthropic.claude-sonnet-4-6-20250514-v1:0") == 200_000
+        assert get_bedrock_context_length("anthropic.claude-sonnet-4-6-20250514-v1:0") == 1_000_000
 
     def test_nova_pro(self):
         from agent.bedrock_adapter import get_bedrock_context_length
@@ -1120,7 +1145,7 @@ def test_unknown_model_gets_default(self):
     def test_inference_profile_resolves(self):
         from agent.bedrock_adapter import get_bedrock_context_length
         # Cross-region inference profiles contain the base model ID
-        assert get_bedrock_context_length("us.anthropic.claude-sonnet-4-6") == 200_000
+        assert get_bedrock_context_length("us.anthropic.claude-sonnet-4-6") == 1_000_000
 
     def test_longest_prefix_wins(self):
         from agent.bedrock_adapter import get_bedrock_context_length

tests/agent/test_model_metadata.py

@@ -1007,6 +1007,49 @@ def test_bedrock_provider_returns_static_table_before_probe(self, mock_fetch):
         assert ctx == 200000
         mock_fetch.assert_not_called()
 
+    @patch("agent.model_metadata.fetch_endpoint_model_metadata")
+    def test_bedrock_claude_4_6_resolves_to_1m_before_probe(self, mock_fetch):
+        """Claude 4.6 Bedrock IDs resolve to the 1M table entry."""
+        ctx = get_model_context_length(
+            "us.anthropic.claude-sonnet-4-6",
+            provider="bedrock",
+            base_url="https://bedrock-runtime.us-east-2.amazonaws.com",
+        )
+        assert ctx == 1_000_000
+        mock_fetch.assert_not_called()
+
+    @patch("agent.model_metadata.fetch_endpoint_model_metadata")
+    def test_bedrock_claude_fable_resolves_to_1m_not_128k_default(self, mock_fetch):
+        """Fable on Bedrock must hit its own table entry, not the 128K default.
+
+        DEFAULT_CONTEXT_LENGTHS maps claude-fable-5 -> 1M, but the Bedrock
+        branch at step 1b returns get_bedrock_context_length() before that
+        catalog is ever consulted — so a missing BEDROCK_CONTEXT_LENGTHS
+        entry silently reported 128K for a 1M model.
+        """
+        ctx = get_model_context_length(
+            "global.anthropic.claude-fable-5",
+            provider="bedrock",
+            base_url="https://bedrock-runtime.us-east-2.amazonaws.com",
+        )
+        assert ctx == 1_000_000
+        mock_fetch.assert_not_called()
+
+    @patch("agent.model_metadata.fetch_endpoint_model_metadata")
+    def test_bedrock_claude_4_6_ignores_stale_200k_cache(self, mock_fetch, tmp_path):
+        """Old 200K Bedrock cache entries must not mask the 1M table entry."""
+        cache_file = tmp_path / "context_length_cache.yaml"
+        base_url = "https://bedrock-runtime.us-east-2.amazonaws.com"
+        with patch("agent.model_metadata._get_context_cache_path", return_value=cache_file):
+            save_context_length("us.anthropic.claude-sonnet-4-6", base_url, 200_000)
+            ctx = get_model_context_length(
+                "us.anthropic.claude-sonnet-4-6",
+                provider="bedrock",
+                base_url=base_url,
+            )
+        assert ctx == 1_000_000
+        mock_fetch.assert_not_called()
+
     @patch("agent.model_metadata.fetch_endpoint_model_metadata")
     def test_bedrock_url_without_provider_hint(self, mock_fetch):
         """bedrock-runtime host infers Bedrock even when provider is omitted."""