From 6e64c39ddccfac7cbb61bef90a9bf15a2bb37934 Mon Sep 17 00:00:00 2001
From: Alex Castillo <alex.castillog33@gmail.com>
Date: Fri, 2 Oct 2026 20:44:51 -0400
Subject: [PATCH 1/5] fix(anthropic): remap disabled thinking to between_tools
 on Sonnet 5.5

maybe_drop_disabled_thinking dropped thinking={type: disabled} for every
always-on-thinking model, including Sonnet 5.5, which silently left thinking
on at whatever effort the caller set. Sonnet 5.5 has a real off-equivalent,
between_tools, valid at low/medium/high effort. Remap to that instead of
dropping, and keep the existing drop-and-warn path for xhigh/max effort
(where between_tools 400s) and for every other always-on-thinking family,
whose own off-equivalent is not confirmed yet.

Fixes #44298
---
 litellm/llms/anthropic/common_utils.py        | 43 +++++++++++++--
 ...odel_prices_and_context_window_backup.json | 16 ++++++
 litellm/types/llms/anthropic.py               |  2 +-
 litellm/types/utils.py                        |  1 +
 model_prices_and_context_window.json          | 16 ++++++
 model_prices_and_context_window.schema.json   |  3 ++
 .../anthropic/test_anthropic_common_utils.py  | 53 +++++++++++++++++++
 tests/unit/test_claude_sonnet_5_config.py     | 28 ++++++++--
 8 files changed, 155 insertions(+), 7 deletions(-)

diff --git a/litellm/llms/anthropic/common_utils.py b/litellm/llms/anthropic/common_utils.py
index 65c2fccceeb..dff8a1de385 100644
--- a/litellm/llms/anthropic/common_utils.py
+++ b/litellm/llms/anthropic/common_utils.py
@@ -57,6 +57,11 @@ DROP_DISABLED_THINKING_WARNING: Final = (
     "disabled (the alternative is a provider 400). The model will still think adaptively, its response can contain "
     "thinking blocks, and those thinking tokens are billed as output tokens."
 )
+REMAP_DISABLED_TO_BETWEEN_TOOLS_WARNING: Final = (
+    "Replacing `thinking={'type': 'disabled'}` with `thinking={'type': 'between_tools'}` for model=%s: this model "
+    "400s on `disabled`, and `between_tools` is its lowest thinking setting. The model will not think before "
+    "responding; progress notes it writes between tool calls still come back as `thinking` blocks."
+)
 
 # Anthropic error `type` (both the JSON error body and SSE `event: error`
 # payloads use this field) mapped to the HTTP status code it corresponds to.
@@ -713,6 +718,28 @@ class AnthropicModelInfo(BaseLLMModelInfo):
         """
         return AnthropicModelInfo._supports_model_capability(model, "thinking_always_on", custom_llm_provider)
 
+    @staticmethod
+    def _supports_between_tools_thinking(model: str, custom_llm_provider: str) -> bool:
+        """Whether ``model`` accepts ``thinking.type=between_tools`` as its off-equivalent
+        setting for an always-on-thinking model. The model cost map is authoritative: an
+        explicit ``supports_between_tools_thinking`` entry resolved under
+        ``custom_llm_provider``. Sonnet 5.5 is the only family with this entry today;
+        other always-on-thinking families fall back to the drop-and-warn path in
+        ``maybe_drop_disabled_thinking`` until their own off-equivalent is confirmed.
+        """
+        return AnthropicModelInfo._supports_model_capability(
+            model, "supports_between_tools_thinking", custom_llm_provider
+        )
+
+    @staticmethod
+    def _effort_rejects_between_tools(optional_params: Mapping[str, object]) -> bool:
+        """``thinking.type=between_tools`` 400s at ``xhigh``/``max`` effort; those levels
+        keep adaptive thinking as their only valid off-equivalent."""
+        output_config: Final = optional_params.get("output_config")
+        if not isinstance(output_config, dict):
+            return False
+        return output_config.get("effort") in ("xhigh", "max")
+
     @staticmethod
     def _supports_legacy_thinking(model: str, custom_llm_provider: str) -> bool:
         """Whether ``model`` is an adaptive-thinking model that still accepts legacy
@@ -729,14 +756,24 @@ class AnthropicModelInfo(BaseLLMModelInfo):
         optional_params: MutableMapping[str, object],  # mutable-ok: in-place out-param, as in _maybe_drop_speed_param
         custom_llm_provider: str,
     ) -> None:
-        """Omit ``thinking={'type': 'disabled'}`` for always-on-thinking models
-        (Fable 5 / Mythos 5), which 400 on it; omission is the API-documented
-        remedy and yields the model's default adaptive thinking."""
+        """Replace ``thinking={'type': 'disabled'}`` for always-on-thinking models
+        (Fable 5 / Mythos 5, Sonnet 5.5, Opus 5.5), which 400 on it. Sonnet 5.5 has a
+        real off-equivalent, ``between_tools``, valid at `low`/`medium`/`high` effort;
+        remap to that instead of silently leaving thinking on at whatever effort the
+        caller set. Every other always-on-thinking family falls back to omitting
+        ``thinking``, the API-documented remedy, which yields the model's default
+        adaptive thinking."""
         thinking: Final = optional_params.get("thinking")
         if not isinstance(thinking, dict) or thinking.get("type") != "disabled":
             return
         if not AnthropicModelInfo._is_always_on_thinking_model(model, custom_llm_provider):
             return
+        if AnthropicModelInfo._supports_between_tools_thinking(
+            model, custom_llm_provider
+        ) and not AnthropicModelInfo._effort_rejects_between_tools(optional_params):
+            litellm.verbose_logger.warning(REMAP_DISABLED_TO_BETWEEN_TOOLS_WARNING, model)
+            optional_params["thinking"] = {"type": "between_tools"}
+            return
         litellm.verbose_logger.warning(
             DROP_DISABLED_THINKING_WARNING,
             model,
diff --git a/litellm/model_prices_and_context_window_backup.json b/litellm/model_prices_and_context_window_backup.json
index 12e4760ed3a..800e4de6c74 100644
--- a/litellm/model_prices_and_context_window_backup.json
+++ b/litellm/model_prices_and_context_window_backup.json
@@ -15057,6 +15057,7 @@
         "supports_output_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://platform.claude.com/docs/en/models/sonnet-5-5/overview",
         "supports_web_search": true
@@ -59065,6 +59066,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://docs.aws.amazon.com/bedrock/latest/userguide/model-card-anthropic-claude-sonnet-5-5.html"
     },
@@ -65798,6 +65800,7 @@
         "output_cost_per_token": 1.2e-05,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
         "supports_assistant_prefill": false,
@@ -78708,6 +78711,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonBedrockFoundationModels/current/index.json"
     },
@@ -78739,6 +78743,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "cache_creation_input_token_cost_above_1hr": 4.4e-06,
         "cache_creation_input_token_cost": 2.75e-06,
@@ -78785,6 +78790,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -78820,6 +78826,7 @@
         "supports_max_reasoning_effort": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512
     },
     "bedrock/us-gov-east-1/anthropic.claude-sonnet-5-5": {
@@ -78838,6 +78845,7 @@
         "output_cost_per_token": 1.2e-05,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
         "supports_assistant_prefill": false,
@@ -78873,6 +78881,7 @@
         "output_cost_per_token": 1.2e-05,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
         "supports_assistant_prefill": false,
@@ -78930,6 +78939,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -78971,6 +78981,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -79012,6 +79023,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -79134,6 +79146,7 @@
         "output_cost_per_token": 1.2e-05,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/",
         "supports_adaptive_thinking": true,
@@ -79192,6 +79205,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -79232,6 +79246,7 @@
         "supports_max_reasoning_effort": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://cloud.google.com/gemini-enterprise-agent-platform/generative-ai/pricing"
     },
@@ -79272,6 +79287,7 @@
         "supports_max_reasoning_effort": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://cloud.google.com/gemini-enterprise-agent-platform/generative-ai/pricing"
     },
diff --git a/litellm/types/llms/anthropic.py b/litellm/types/llms/anthropic.py
index ee357cd6581..67cb38d2bcb 100644
--- a/litellm/types/llms/anthropic.py
+++ b/litellm/types/llms/anthropic.py
@@ -731,7 +731,7 @@ ANTHROPIC_API_ONLY_HEADERS: Final = {  # fails if calling anthropic on vertex ai
 
 
 class AnthropicThinkingParam(TypedDict, total=False):
-    type: ReadOnly[Literal["enabled", "adaptive", "disabled"]]
+    type: ReadOnly[Literal["enabled", "adaptive", "disabled", "between_tools"]]
     budget_tokens: int
     display: ReadOnly[Literal["summarized", "omitted", "updates"]]
 
diff --git a/litellm/types/utils.py b/litellm/types/utils.py
index 8c10b9e3497..7910983c4b7 100644
--- a/litellm/types/utils.py
+++ b/litellm/types/utils.py
@@ -193,6 +193,7 @@ class ProviderSpecificModelInfo(TypedDict, total=False):
     supports_adaptive_thinking: bool | None
     supports_legacy_thinking: ReadOnly[bool | None]
     thinking_always_on: ReadOnly[bool | None]
+    supports_between_tools_thinking: ReadOnly[bool | None]
     supports_tool_search: bool | None
     supports_mid_conversation_system: bool | None
     supports_url_context: bool | None
diff --git a/model_prices_and_context_window.json b/model_prices_and_context_window.json
index 12e4760ed3a..800e4de6c74 100644
--- a/model_prices_and_context_window.json
+++ b/model_prices_and_context_window.json
@@ -15057,6 +15057,7 @@
         "supports_output_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://platform.claude.com/docs/en/models/sonnet-5-5/overview",
         "supports_web_search": true
@@ -59065,6 +59066,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://docs.aws.amazon.com/bedrock/latest/userguide/model-card-anthropic-claude-sonnet-5-5.html"
     },
@@ -65798,6 +65800,7 @@
         "output_cost_per_token": 1.2e-05,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
         "supports_assistant_prefill": false,
@@ -78708,6 +78711,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonBedrockFoundationModels/current/index.json"
     },
@@ -78739,6 +78743,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "cache_creation_input_token_cost_above_1hr": 4.4e-06,
         "cache_creation_input_token_cost": 2.75e-06,
@@ -78785,6 +78790,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -78820,6 +78826,7 @@
         "supports_max_reasoning_effort": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512
     },
     "bedrock/us-gov-east-1/anthropic.claude-sonnet-5-5": {
@@ -78838,6 +78845,7 @@
         "output_cost_per_token": 1.2e-05,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
         "supports_assistant_prefill": false,
@@ -78873,6 +78881,7 @@
         "output_cost_per_token": 1.2e-05,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "supports_adaptive_thinking": true,
         "supports_assistant_prefill": false,
@@ -78930,6 +78939,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -78971,6 +78981,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -79012,6 +79023,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -79134,6 +79146,7 @@
         "output_cost_per_token": 1.2e-05,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/",
         "supports_adaptive_thinking": true,
@@ -79192,6 +79205,7 @@
         "supports_parallel_tool_use_config": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://aws.amazon.com/bedrock/pricing/"
     },
@@ -79232,6 +79246,7 @@
         "supports_max_reasoning_effort": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://cloud.google.com/gemini-enterprise-agent-platform/generative-ai/pricing"
     },
@@ -79272,6 +79287,7 @@
         "supports_max_reasoning_effort": true,
         "supports_forced_tool_use": false,
         "thinking_always_on": true,
+        "supports_between_tools_thinking": true,
         "prompt_cache_min_tokens": 512,
         "source": "https://cloud.google.com/gemini-enterprise-agent-platform/generative-ai/pricing"
     },
diff --git a/model_prices_and_context_window.schema.json b/model_prices_and_context_window.schema.json
index cdf023e71ef..104380c0fe3 100644
--- a/model_prices_and_context_window.schema.json
+++ b/model_prices_and_context_window.schema.json
@@ -990,6 +990,9 @@
         "supports_audio_output": {
           "type": "boolean"
         },
+        "supports_between_tools_thinking": {
+          "type": "boolean"
+        },
         "supports_computer_use": {
           "type": "boolean"
         },
diff --git a/tests/unit/llms/anthropic/test_anthropic_common_utils.py b/tests/unit/llms/anthropic/test_anthropic_common_utils.py
index 68e2e9650d5..9f9133dfbc9 100644
--- a/tests/unit/llms/anthropic/test_anthropic_common_utils.py
+++ b/tests/unit/llms/anthropic/test_anthropic_common_utils.py
@@ -2504,3 +2504,56 @@ def test_tool_changes_beta_requires_system_tool_reference(role: str, content: ob
     )
 
     assert ANTHROPIC_MID_CONVERSATION_TOOL_CHANGES_BETA_HEADER not in headers.get("anthropic-beta", "").split(",")
+
+
+@pytest.mark.parametrize("effort", (None, "low", "medium", "high"))
+def test_maybe_drop_disabled_thinking_remaps_sonnet_5_5_to_between_tools(
+    local_model_cost_map: None, effort: str | None
+) -> None:
+    from litellm.llms.anthropic.common_utils import AnthropicModelInfo
+
+    optional_params: Final[dict[str, object]] = {"thinking": {"type": "disabled"}}
+    if effort is not None:
+        optional_params["output_config"] = {"effort": effort}
+
+    AnthropicModelInfo.maybe_drop_disabled_thinking(
+        model="claude-sonnet-5-5",
+        optional_params=optional_params,
+        custom_llm_provider="anthropic",
+    )
+
+    assert optional_params["thinking"] == {"type": "between_tools"}
+
+
+@pytest.mark.parametrize("effort", ("xhigh", "max"))
+def test_maybe_drop_disabled_thinking_drops_for_sonnet_5_5_at_rejecting_effort(
+    local_model_cost_map: None, effort: str
+) -> None:
+    from litellm.llms.anthropic.common_utils import AnthropicModelInfo
+
+    optional_params: Final[dict[str, object]] = {
+        "thinking": {"type": "disabled"},
+        "output_config": {"effort": effort},
+    }
+
+    AnthropicModelInfo.maybe_drop_disabled_thinking(
+        model="claude-sonnet-5-5",
+        optional_params=optional_params,
+        custom_llm_provider="anthropic",
+    )
+
+    assert "thinking" not in optional_params
+
+
+def test_maybe_drop_disabled_thinking_still_drops_for_opus_5_5(local_model_cost_map: None) -> None:
+    from litellm.llms.anthropic.common_utils import AnthropicModelInfo
+
+    optional_params: Final[dict[str, object]] = {"thinking": {"type": "disabled"}}
+
+    AnthropicModelInfo.maybe_drop_disabled_thinking(
+        model="claude-opus-5-5",
+        optional_params=optional_params,
+        custom_llm_provider="anthropic",
+    )
+
+    assert "thinking" not in optional_params
diff --git a/tests/unit/test_claude_sonnet_5_config.py b/tests/unit/test_claude_sonnet_5_config.py
index 36078ff494f..0f6eeb81ad9 100644
--- a/tests/unit/test_claude_sonnet_5_config.py
+++ b/tests/unit/test_claude_sonnet_5_config.py
@@ -10,8 +10,10 @@ populate ``litellm.anthropic_models`` at import, which is what lets a bare
 ``anthropic/*`` wildcard deployment).
 
 Sonnet 5.5 (``claude-sonnet-5-5``) is covered here too. It carries the same
-gen-5 profile but thinking cannot be turned off and forced tool use is not
-supported, same as Opus 5.5
+gen-5 profile, and forced tool use is not supported, same as Opus 5.5. Thinking
+cannot be turned off via ``thinking.type=disabled``, the Sonnet 5 shape; the
+off-equivalent is ``thinking.type=between_tools``, which ``maybe_drop_disabled_thinking``
+remaps a caller's ``disabled`` request to.
 """
 
 import json
@@ -79,9 +81,29 @@ def test_sonnet_5_5_present_in_bundled_backup(model_name):
 )
 def test_sonnet_5_5_thinking_profile(local_model_cost_map, model, provider):
     """Sonnet 5.5 has thinking always on with the adaptive thinking surface, and
-    no forced tool use, same as Opus 5.5."""
+    no forced tool use, same as Opus 5.5. Unlike the rest of that family, it also
+    has a real off-equivalent for thinking: between_tools."""
     from litellm.llms.anthropic.common_utils import AnthropicModelInfo
 
     assert AnthropicModelInfo._is_adaptive_thinking_model(model, provider) is True
     assert AnthropicModelInfo._is_always_on_thinking_model(model, provider) is True
+    assert AnthropicModelInfo._supports_between_tools_thinking(model, provider) is True
     assert AnthropicModelInfo.forced_tool_use_unsupported(model.removeprefix("anthropic/")) is True
+
+
+@pytest.mark.parametrize(
+    ("model", "provider"),
+    [
+        ("claude-opus-5-5", "anthropic"),
+        ("claude-fable-5", "anthropic"),
+        ("claude-mythos-5", "anthropic"),
+    ],
+)
+def test_other_always_on_thinking_models_lack_between_tools(local_model_cost_map, model, provider):
+    """Sonnet 5.5 is the only always-on-thinking family with a confirmed
+    between_tools off-equivalent today; the rest must keep falling back to the
+    drop-and-warn path in maybe_drop_disabled_thinking."""
+    from litellm.llms.anthropic.common_utils import AnthropicModelInfo
+
+    assert AnthropicModelInfo._is_always_on_thinking_model(model, provider) is True
+    assert AnthropicModelInfo._supports_between_tools_thinking(model, provider) is False

From 2927cbd1e3172b2f7690080e97694982b0574102 Mon Sep 17 00:00:00 2001
From: Alex Castillo <alex.castillog33@gmail.com>
Date: Fri, 2 Oct 2026 21:13:24 -0400
Subject: [PATCH 2/5] fix(anthropic): add supports_between_tools_thinking to
 the test_utils.py cost-map schema

test_aaamodel_prices_and_context_window_json_is_valid validates the cost map
against its own copy of the schema, separate from
model_prices_and_context_window.schema.json. Missed updating it in the
previous commit.
---
 tests/unit/test_utils.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index ab7ecfcda05..ed94b54d138 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -975,6 +975,7 @@ def test_aaamodel_prices_and_context_window_json_is_valid():
                 "supports_anthropic_thinking_payload": {"type": "boolean"},
                 "supports_legacy_thinking": {"type": "boolean"},
                 "thinking_always_on": {"type": "boolean"},
+                "supports_between_tools_thinking": {"type": "boolean"},
                 "supports_mid_conversation_system": {"type": "boolean"},
                 "supports_sampling_params": {"type": "boolean"},
                 "supports_output_config": {"type": "boolean"},

From 601a4092d09a50202178786e806816ee7cbdeb55 Mon Sep 17 00:00:00 2001
From: Alex Castillo <alex.castillog33@gmail.com>
Date: Mon, 5 Oct 2026 02:54:58 -0400
Subject: [PATCH 3/5] fix(anthropic): keep disabled thinking through the
 missing-thinking-blocks guard

With modify_params=True, a tool-result turn whose assistant history has no
thinking_blocks dropped thinking={'type': 'disabled'} before
maybe_drop_disabled_thinking could remap it to between_tools on Sonnet 5.5,
so the provider fell back to adaptive thinking. Disabled thinking needs no
thinking_blocks, so both the chat and Converse guards now skip it
---
 litellm/llms/anthropic/chat/transformation.py |  2 +-
 .../bedrock/chat/converse_transformation.py   |  2 +-
 .../test_anthropic_chat_transformation.py     | 26 ++++++++++++++++++
 .../chat/test_converse_transformation.py      | 27 +++++++++++++++++++
 4 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/litellm/llms/anthropic/chat/transformation.py b/litellm/llms/anthropic/chat/transformation.py
index 490912d42eb..d8dc9186b39 100644
--- a/litellm/llms/anthropic/chat/transformation.py
+++ b/litellm/llms/anthropic/chat/transformation.py
@@ -1921,7 +1921,7 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
         # Anthropic errors with: "When thinking is disabled, an assistant message cannot contain thinking"
         # Related issue: https://github.com/BerriAI/litellm/issues/18926
         if (
-            optional_params.get("thinking") is not None
+            optional_params.get("thinking") not in (None, {"type": "disabled"})
             and messages is not None
             and last_assistant_with_tool_calls_has_no_thinking_blocks(messages)
             and not any_assistant_message_has_thinking_blocks(messages)
diff --git a/litellm/llms/bedrock/chat/converse_transformation.py b/litellm/llms/bedrock/chat/converse_transformation.py
index 48a8b1b44bb..bbefd851801 100644
--- a/litellm/llms/bedrock/chat/converse_transformation.py
+++ b/litellm/llms/bedrock/chat/converse_transformation.py
@@ -1875,7 +1875,7 @@ class AmazonConverseConfig(BaseConfig):
         # If any message has thinking_blocks, we must keep thinking enabled, otherwise
         # Related issues: https://github.com/BerriAI/litellm/issues/14194
         if (
-            optional_params.get("thinking") is not None
+            optional_params.get("thinking") not in (None, {"type": "disabled"})
             and messages is not None
             and last_assistant_with_tool_calls_has_no_thinking_blocks(messages)
             and not any_assistant_message_has_thinking_blocks(messages)
diff --git a/tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py b/tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py
index 332153b4c7d..2fa71e63292 100644
--- a/tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py
+++ b/tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py
@@ -6798,3 +6798,29 @@ def test_chat_dummy_tool_result_for_an_orphaned_tool_call_replays_a_byte_identic
     _assert_prefix_stable(requests)
     assert [m["role"] for m in requests[0]["messages"]] == ["user", "assistant", "user"]
     assert requests[0]["messages"][2]["content"][0]["type"] == "tool_result"
+
+
+def test_disabled_thinking_on_sonnet_5_5_tool_result_turn_remaps_to_between_tools(local_model_cost_map, monkeypatch):
+    monkeypatch.setattr(litellm, "modify_params", True)
+    messages: Final = [
+        {"role": "user", "content": "Look it up"},
+        {
+            "role": "assistant",
+            "content": None,
+            "tool_calls": [{"id": "call_1", "type": "function", "function": {"name": "lookup", "arguments": "{}"}}],
+        },
+        {"role": "tool", "tool_call_id": "call_1", "content": "found"},
+    ]
+    tools: Final = [
+        {"name": "lookup", "description": "Look something up", "input_schema": {"type": "object", "properties": {}}}
+    ]
+
+    request: Final = AnthropicConfig().transform_request(
+        model="claude-sonnet-5-5",
+        messages=messages,
+        optional_params={"tools": tools, "thinking": {"type": "disabled"}},
+        litellm_params={},
+        headers={},
+    )
+
+    assert request["thinking"] == {"type": "between_tools"}
diff --git a/tests/unit/llms/bedrock/chat/test_converse_transformation.py b/tests/unit/llms/bedrock/chat/test_converse_transformation.py
index f6f98e3b9bd..95c0a6b78a7 100644
--- a/tests/unit/llms/bedrock/chat/test_converse_transformation.py
+++ b/tests/unit/llms/bedrock/chat/test_converse_transformation.py
@@ -7347,6 +7347,33 @@ def test_disabled_thinking_omitted_for_always_on_models_converse(
     else:
         assert additional.get("thinking") == {"type": "disabled"}
 
+
+def test_disabled_thinking_on_sonnet_5_5_tool_result_turn_remaps_to_between_tools_converse(
+    local_model_cost_map, monkeypatch
+):
+    monkeypatch.setattr(litellm, "modify_params", True)
+    messages: Final = [
+        {"role": "user", "content": "Look it up"},
+        {
+            "role": "assistant",
+            "content": None,
+            "tool_calls": [{"id": "call_1", "type": "function", "function": {"name": "lookup", "arguments": "{}"}}],
+        },
+        {"role": "tool", "tool_call_id": "call_1", "content": "found"},
+    ]
+    tools: Final = [{"type": "function", "function": {"name": "lookup", "parameters": {"type": "object"}}}]
+
+    result: Final = AmazonConverseConfig()._transform_request(
+        model="us.anthropic.claude-sonnet-5-5",
+        messages=messages,
+        optional_params={"maxTokens": 64, "tools": tools, "thinking": {"type": "disabled"}},
+        litellm_params={},
+        headers={},
+    )
+
+    assert result.get("additionalModelRequestFields", {}).get("thinking") == {"type": "between_tools"}
+
+
 @pytest.mark.parametrize(
     "model",
     ["anthropic.claude-fable-5-1", "us.anthropic.claude-fable-5-1"],

From 4142eace346996d9a99b593712326907c8d90c6b Mon Sep 17 00:00:00 2001
From: Alex Castillo <alex.castillog33@gmail.com>
Date: Mon, 12 Oct 2026 01:49:17 -0400
Subject: [PATCH 4/5] chore(anthropic): mark the between_tools remap as an
 intended in-place write

maybe_drop_disabled_thinking mutates optional_params by design (its
signature already carries mutable-ok); annotate the new store so the
type-discipline gate's LIT011 ceiling doesn't grow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 litellm/llms/anthropic/common_utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/litellm/llms/anthropic/common_utils.py b/litellm/llms/anthropic/common_utils.py
index 65ef0cc6c7d..77702146790 100644
--- a/litellm/llms/anthropic/common_utils.py
+++ b/litellm/llms/anthropic/common_utils.py
@@ -944,7 +944,7 @@ class AnthropicModelInfo(BaseLLMModelInfo):
             model, custom_llm_provider
         ) and not AnthropicModelInfo._effort_rejects_between_tools(optional_params):
             litellm.verbose_logger.warning(REMAP_DISABLED_TO_BETWEEN_TOOLS_WARNING, model)
-            optional_params["thinking"] = {"type": "between_tools"}
+            optional_params["thinking"] = {"type": "between_tools"}  # rebind-ok: in-place out-param, see signature
             return
         litellm.verbose_logger.warning(
             DROP_DISABLED_THINKING_WARNING,

From c572b9910fec8419a69fd2fa6f7d92d4e869ed67 Mon Sep 17 00:00:00 2001
From: Alex Castillo <alex.castillog33@gmail.com>
Date: Mon, 12 Oct 2026 02:17:56 -0400
Subject: [PATCH 5/5] chore(anthropic): read output_config.effort without an
 untyped dict.get

The bare dict narrowed from optional_params has unknown key/value types,
so .get() added a reportUnknownMemberType error past the basedpyright
ceiling. A membership check plus subscript reads the same value without
the member access.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 litellm/llms/anthropic/common_utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/litellm/llms/anthropic/common_utils.py b/litellm/llms/anthropic/common_utils.py
index 77702146790..c6e1546f53a 100644
--- a/litellm/llms/anthropic/common_utils.py
+++ b/litellm/llms/anthropic/common_utils.py
@@ -910,7 +910,7 @@ class AnthropicModelInfo(BaseLLMModelInfo):
         output_config: Final = optional_params.get("output_config")
         if not isinstance(output_config, dict):
             return False
-        return output_config.get("effort") in ("xhigh", "max")
+        return "effort" in output_config and output_config["effort"] in ("xhigh", "max")
 
     @staticmethod
     def _supports_legacy_thinking(model: str, custom_llm_provider: str) -> bool: