feat: add context window limit lookup table

Author: opieter-aws

src/strands/models/_defaults.py

@@ -0,0 +1,153 @@
+"""Default model metadata lookup tables.
+
+Provides context window limits for known model IDs across all providers.
+Values sourced from provider documentation and
+https://github.com/BerriAI/litellm/blob/litellm_internal_staging/model_prices_and_context_window.json
+"""
+
+from typing import Any, TypeVar
+
+_T = TypeVar("_T", bound=dict[str, Any])
+
+# Context window limits (in tokens) for known model IDs.
+#
+# Best-effort lookup table — unknown models return None and callers
+# fall back gracefully (e.g. proactive compression is disabled).
+# Users can always override with an explicit context_window_limit in their model config.
+#
+# For Bedrock models with cross-region prefixes (e.g. us., eu., global.),
+# get_context_window_limit strips the prefix before lookup so only the base model ID is needed here.
+_CONTEXT_WINDOW_LIMITS: dict[str, int] = {
+    # Anthropic (direct API)
+    "claude-sonnet-4-6": 1_000_000,
+    "claude-sonnet-4-20250514": 1_000_000,
+    "claude-sonnet-4-5": 200_000,
+    "claude-sonnet-4-5-20250929": 200_000,
+    "claude-opus-4-6": 1_000_000,
+    "claude-opus-4-6-20260205": 1_000_000,
+    "claude-opus-4-7": 1_000_000,
+    "claude-opus-4-7-20260416": 1_000_000,
+    "claude-opus-4-5": 200_000,
+    "claude-opus-4-5-20251101": 200_000,
+    "claude-opus-4-20250514": 200_000,
+    "claude-opus-4-1": 200_000,
+    "claude-opus-4-1-20250805": 200_000,
+    "claude-haiku-4-5": 200_000,
+    "claude-haiku-4-5-20251001": 200_000,
+    "claude-3-7-sonnet-20250219": 200_000,
+    "claude-3-5-sonnet-20241022": 200_000,
+    "claude-3-5-sonnet-20240620": 200_000,
+    "claude-3-5-haiku-20241022": 200_000,
+    "claude-3-opus-20240229": 200_000,
+    "claude-3-haiku-20240307": 200_000,
+    # Bedrock Anthropic (base model IDs — cross-region prefixes stripped by get_context_window_limit)
+    "anthropic.claude-sonnet-4-6": 1_000_000,
+    "anthropic.claude-sonnet-4-20250514-v1:0": 1_000_000,
+    "anthropic.claude-sonnet-4-5-20250929-v1:0": 200_000,
+    "anthropic.claude-opus-4-6-v1": 1_000_000,
+    "anthropic.claude-opus-4-7": 1_000_000,
+    "anthropic.claude-opus-4-5-20251101-v1:0": 200_000,
+    "anthropic.claude-opus-4-20250514-v1:0": 200_000,
+    "anthropic.claude-opus-4-1-20250805-v1:0": 200_000,
+    "anthropic.claude-haiku-4-5-20251001-v1:0": 200_000,
+    "anthropic.claude-haiku-4-5@20251001": 200_000,
+    "anthropic.claude-3-7-sonnet-20250219-v1:0": 200_000,
+    "anthropic.claude-3-7-sonnet-20240620-v1:0": 200_000,
+    "anthropic.claude-3-5-sonnet-20241022-v2:0": 200_000,
+    "anthropic.claude-3-5-sonnet-20240620-v1:0": 200_000,
+    "anthropic.claude-3-5-haiku-20241022-v1:0": 200_000,
+    "anthropic.claude-3-opus-20240229-v1:0": 200_000,
+    "anthropic.claude-3-haiku-20240307-v1:0": 200_000,
+    "anthropic.claude-3-sonnet-20240229-v1:0": 200_000,
+    "anthropic.claude-mythos-preview": 1_000_000,
+    # Bedrock Amazon Nova
+    "amazon.nova-pro-v1:0": 300_000,
+    "amazon.nova-lite-v1:0": 300_000,
+    "amazon.nova-micro-v1:0": 128_000,
+    "amazon.nova-premier-v1:0": 1_000_000,
+    "amazon.nova-2-lite-v1:0": 1_000_000,
+    "amazon.nova-2-pro-preview-20251202-v1:0": 1_000_000,
+    # OpenAI
+    "gpt-5.5": 1_050_000,
+    "gpt-5.5-pro": 1_050_000,
+    "gpt-5.4": 1_050_000,
+    "gpt-5.4-pro": 1_050_000,
+    "gpt-5.4-mini": 272_000,
+    "gpt-5.4-nano": 272_000,
+    "gpt-5.2": 272_000,
+    "gpt-5.2-pro": 272_000,
+    "gpt-5.1": 272_000,
+    "gpt-5": 272_000,
+    "gpt-5-mini": 272_000,
+    "gpt-5-nano": 272_000,
+    "gpt-5-pro": 128_000,
+    "gpt-4.1": 1_047_576,
+    "gpt-4.1-mini": 1_047_576,
+    "gpt-4.1-nano": 1_047_576,
+    "gpt-4o": 128_000,
+    "gpt-4o-mini": 128_000,
+    "gpt-4-turbo": 128_000,
+    "o3": 200_000,
+    "o3-mini": 200_000,
+    "o3-pro": 200_000,
+    "o4-mini": 200_000,
+    "o1": 200_000,
+    # Google Gemini
+    "gemini-2.5-flash": 1_048_576,
+    "gemini-2.5-flash-lite": 1_048_576,
+    "gemini-2.5-pro": 1_048_576,
+    "gemini-2.0-flash": 1_048_576,
+    "gemini-2.0-flash-lite": 1_048_576,
+    "gemini-3-pro-preview": 1_048_576,
+    "gemini-3-flash-preview": 1_048_576,
+    "gemini-3.1-pro-preview": 1_048_576,
+    "gemini-3.1-flash-lite-preview": 1_048_576,
+}
+
+
+def get_context_window_limit(model_id: str) -> int | None:
+    """Look up the context window limit for a model ID.
+
+    For Bedrock cross-region model IDs (e.g. ``us.anthropic.claude-sonnet-4-6``),
+    the region prefix is stripped as a fallback if the direct lookup fails.
+
+    Args:
+        model_id: The model ID to look up.
+
+    Returns:
+        The context window limit in tokens, or None if not found.
+    """
+    direct = _CONTEXT_WINDOW_LIMITS.get(model_id)
+    if direct is not None:
+        return direct
+
+    # Fallback: strip prefix before first dot and retry (handles cross-region prefixes)
+    dot_index = model_id.find(".")
+    if dot_index != -1:
+        return _CONTEXT_WINDOW_LIMITS.get(model_id[dot_index + 1 :])
+
+    return None
+
+
+def resolve_config_metadata(config: _T, model_id: str) -> _T:
+    """Resolve model metadata fields on a config dict from built-in lookup tables.
+
+    When ``context_window_limit`` is not explicitly set, looks it up from the built-in table.
+    Explicit values pass through unchanged. Returns a new dict only when resolution adds a field;
+    otherwise returns the original config to avoid unnecessary allocation.
+
+    Args:
+        config: The stored model config dict.
+        model_id: The model ID to look up.
+
+    Returns:
+        The config with resolved metadata, or the original config if nothing to resolve.
+    """
+    if "context_window_limit" in config:
+        return config
+
+    limit = get_context_window_limit(model_id)
+    if limit is None:
+        return config
+
+    return {**config, "context_window_limit": limit}  # type: ignore[return-value]

src/strands/models/anthropic.py

@@ -20,6 +20,7 @@
 from ..types.exceptions import ContextWindowOverflowException, ModelThrottledException
 from ..types.streaming import StreamEvent
 from ..types.tools import ToolChoice, ToolChoiceToolDict, ToolSpec
+from ._defaults import resolve_config_metadata
 from ._validation import _has_location_source, validate_config_keys
 from .model import BaseModelConfig, Model
 
@@ -95,7 +96,7 @@ def get_config(self) -> AnthropicConfig:
         Returns:
             The Anthropic model configuration.
         """
-        return self.config
+        return resolve_config_metadata(self.config, self.config["model_id"])
 
     def _format_request_message_content(self, content: ContentBlock) -> dict[str, Any]:
         """Format an Anthropic content block.

src/strands/models/bedrock.py

@@ -31,6 +31,7 @@
 )
 from ..types.streaming import CitationsDelta, StreamEvent
 from ..types.tools import ToolChoice, ToolSpec
+from ._defaults import resolve_config_metadata
 from ._strict_schema import ensure_strict_json_schema
 from ._validation import validate_config_keys
 from .model import BaseModelConfig, CacheConfig, Model
@@ -217,7 +218,7 @@ def get_config(self) -> BedrockConfig:
         Returns:
             The Bedrock model configuration.
         """
-        return self.config
+        return resolve_config_metadata(self.config, self.config.get("model_id", ""))
 
     def _format_request(
         self,

src/strands/models/gemini.py

@@ -19,6 +19,7 @@
 from ..types.exceptions import ContextWindowOverflowException, ModelThrottledException, ProviderTokenCountError
 from ..types.streaming import StreamEvent
 from ..types.tools import ToolChoice, ToolSpec
+from ._defaults import resolve_config_metadata
 from ._validation import _has_location_source, validate_config_keys
 from .model import BaseModelConfig, Model
 
@@ -115,7 +116,7 @@ def get_config(self) -> GeminiConfig:
         Returns:
             The Gemini model configuration.
         """
-        return self.config
+        return resolve_config_metadata(self.config, self.config["model_id"])
 
     def _get_client(self) -> genai.Client:
         """Get a Gemini client for making requests.

src/strands/models/openai.py

@@ -21,6 +21,7 @@
 from ..types.exceptions import ContextWindowOverflowException, ModelThrottledException
 from ..types.streaming import StreamEvent
 from ..types.tools import ToolChoice, ToolResult, ToolSpec, ToolUse
+from ._defaults import resolve_config_metadata
 from ._openai_bedrock import BedrockMantleConfig, resolve_bedrock_client_args
 from ._validation import _has_location_source, validate_config_keys
 from .model import BaseModelConfig, Model
@@ -150,7 +151,9 @@ def get_config(self) -> OpenAIConfig:
         Returns:
             The OpenAI model configuration.
         """
-        return cast(OpenAIModel.OpenAIConfig, self.config)
+        return cast(
+            OpenAIModel.OpenAIConfig, resolve_config_metadata(self.config, str(self.config.get("model_id", "")))
+        )
 
     @classmethod
     def format_request_message_content(cls, content: ContentBlock, **kwargs: Any) -> dict[str, Any]:

src/strands/models/openai_responses.py

@@ -58,6 +58,7 @@
 from ..types.exceptions import ContextWindowOverflowException, ModelThrottledException  # noqa: E402
 from ..types.streaming import StreamEvent  # noqa: E402
 from ..types.tools import ToolChoice, ToolResult, ToolSpec, ToolUse  # noqa: E402
+from ._defaults import resolve_config_metadata  # noqa: E402
 from ._openai_bedrock import BedrockMantleConfig, resolve_bedrock_client_args  # noqa: E402
 from ._validation import validate_config_keys  # noqa: E402
 from .model import BaseModelConfig, Model  # noqa: E402
@@ -210,7 +211,10 @@ def get_config(self) -> OpenAIResponsesConfig:
         Returns:
             The OpenAI Responses API model configuration.
         """
-        return cast(OpenAIResponsesModel.OpenAIResponsesConfig, self.config)
+        return cast(
+            OpenAIResponsesModel.OpenAIResponsesConfig,
+            resolve_config_metadata(self.config, str(self.config.get("model_id", ""))),
+        )
 
     @override
     async def count_tokens(

tests/strands/models/test_anthropic.py

@@ -82,6 +82,30 @@ def test__init__model_configs(anthropic_client, model_id, max_tokens):
     assert tru_temperature == exp_temperature
 
 
+def test__init__auto_populates_context_window_limit(anthropic_client):
+    _ = anthropic_client
+
+    model = AnthropicModel(model_id="claude-sonnet-4-20250514", max_tokens=1)
+
+    assert model.get_config().get("context_window_limit") == 1_000_000
+
+
+def test__init__explicit_context_window_limit_not_overridden(anthropic_client):
+    _ = anthropic_client
+
+    model = AnthropicModel(model_id="claude-sonnet-4-20250514", max_tokens=1, context_window_limit=100_000)
+
+    assert model.get_config().get("context_window_limit") == 100_000
+
+
+def test__init__unknown_model_no_context_window_limit(anthropic_client):
+    _ = anthropic_client
+
+    model = AnthropicModel(model_id="unknown-model", max_tokens=1)
+
+    assert model.get_config().get("context_window_limit") is None
+
+
 def test_update_config(model, model_id):
     model.update_config(model_id=model_id)
 

tests/strands/models/test_bedrock.py

@@ -296,6 +296,46 @@ def test__init__context_window_limit(bedrock_client):
     assert model.context_window_limit == 200_000
 
 
+def test__init__auto_populates_context_window_limit(bedrock_client):
+    _ = bedrock_client
+
+    model = BedrockModel(model_id="anthropic.claude-sonnet-4-20250514-v1:0")
+
+    assert model.get_config().get("context_window_limit") == 1_000_000
+
+
+def test__init__auto_populates_context_window_limit_cross_region(bedrock_client):
+    _ = bedrock_client
+
+    model = BedrockModel(model_id="us.anthropic.claude-sonnet-4-6")
+
+    assert model.get_config().get("context_window_limit") == 1_000_000
+
+
+def test__init__auto_populates_context_window_limit_default_model(bedrock_client):
+    _ = bedrock_client
+
+    model = BedrockModel()
+
+    assert model.get_config().get("context_window_limit") == 1_000_000
+
+
+def test__init__explicit_context_window_limit_not_overridden(bedrock_client):
+    _ = bedrock_client
+
+    model = BedrockModel(model_id="anthropic.claude-sonnet-4-20250514-v1:0", context_window_limit=100_000)
+
+    assert model.get_config().get("context_window_limit") == 100_000
+
+
+def test__init__unknown_model_no_context_window_limit(bedrock_client):
+    _ = bedrock_client
+
+    model = BedrockModel(model_id="unknown.model-v1:0")
+
+    assert model.get_config().get("context_window_limit") is None
+
+
 def test_update_config(model, model_id):
     model.update_config(model_id=model_id)
 

tests/strands/models/test_defaults.py

@@ -0,0 +1,77 @@
+"""Tests for model metadata lookup tables."""
+
+
+from strands.models._defaults import get_context_window_limit, resolve_config_metadata
+
+
+class TestGetContextWindowLimit:
+    """Tests for get_context_window_limit."""
+
+    def test_known_anthropic_direct_api(self):
+        assert get_context_window_limit("claude-sonnet-4-6") == 1_000_000
+        assert get_context_window_limit("claude-opus-4-6") == 1_000_000
+        assert get_context_window_limit("claude-opus-4-5") == 200_000
+        assert get_context_window_limit("claude-haiku-4-5") == 200_000
+
+    def test_known_bedrock_anthropic(self):
+        assert get_context_window_limit("anthropic.claude-sonnet-4-6") == 1_000_000
+        assert get_context_window_limit("anthropic.claude-haiku-4-5-20251001-v1:0") == 200_000
+
+    def test_known_bedrock_nova(self):
+        assert get_context_window_limit("amazon.nova-pro-v1:0") == 300_000
+        assert get_context_window_limit("amazon.nova-micro-v1:0") == 128_000
+
+    def test_known_openai(self):
+        assert get_context_window_limit("gpt-5.4") == 1_050_000
+        assert get_context_window_limit("gpt-4o") == 128_000
+        assert get_context_window_limit("o3") == 200_000
+        assert get_context_window_limit("o4-mini") == 200_000
+
+    def test_known_gemini(self):
+        assert get_context_window_limit("gemini-2.5-flash") == 1_048_576
+        assert get_context_window_limit("gemini-2.5-pro") == 1_048_576
+
+    def test_strips_bedrock_cross_region_prefix(self):
+        assert get_context_window_limit("us.anthropic.claude-sonnet-4-6") == 1_000_000
+        assert get_context_window_limit("global.anthropic.claude-sonnet-4-6") == 1_000_000
+        assert get_context_window_limit("eu.anthropic.claude-sonnet-4-6") == 1_000_000
+        assert get_context_window_limit("ap.anthropic.claude-sonnet-4-6") == 1_000_000
+
+    def test_strips_any_prefix_as_fallback(self):
+        # Any prefix before the first dot is stripped if direct lookup fails
+        assert get_context_window_limit("custom.anthropic.claude-sonnet-4-6") == 1_000_000
+
+    def test_unknown_model_returns_none(self):
+        assert get_context_window_limit("unknown-model-xyz") is None
+        assert get_context_window_limit("foo.unknown-model-xyz") is None
+
+
+class TestResolveConfigMetadata:
+    """Tests for resolve_config_metadata."""
+
+    def test_resolves_context_window_limit(self):
+        config: dict = {"model_id": "claude-sonnet-4-6"}
+        result = resolve_config_metadata(config, "claude-sonnet-4-6")
+        assert result["context_window_limit"] == 1_000_000
+
+    def test_preserves_explicit_context_window_limit(self):
+        config: dict = {"model_id": "claude-sonnet-4-6", "context_window_limit": 100_000}
+        result = resolve_config_metadata(config, "claude-sonnet-4-6")
+        assert result["context_window_limit"] == 100_000
+
+    def test_returns_original_config_when_explicit(self):
+        config: dict = {"model_id": "claude-sonnet-4-6", "context_window_limit": 100_000}
+        result = resolve_config_metadata(config, "claude-sonnet-4-6")
+        assert result is config
+
+    def test_returns_original_config_when_unknown_model(self):
+        config: dict = {"model_id": "unknown-model"}
+        result = resolve_config_metadata(config, "unknown-model")
+        assert result is config
+        assert "context_window_limit" not in result
+
+    def test_returns_new_dict_when_resolved(self):
+        config: dict = {"model_id": "claude-sonnet-4-6"}
+        result = resolve_config_metadata(config, "claude-sonnet-4-6")
+        assert result is not config
+        assert "context_window_limit" not in config