fix(anthropic/passthrough): drop incompatible temperature when downgrading adaptive thinking for pre-4.6 models (#33244)

* fix(anthropic/passthrough): drop temperature and cap thinking budget when downgrading adaptive thinking for pre-4.6 models

* test(anthropic/passthrough): use sufficient max_tokens for reasoning_effort thinking mapping

* fix(anthropic/passthrough): drop incompatible temperature when downgrading adaptive thinking for pre-4.6 models

Narrow the fix to the temperature reconciliation; the reasoning_effort
budget cap is reverted because the live translation grid relies on
budget_tokens >= max_tokens to reject unsupported effort tiers
(xhigh/max) on budget-mode models, so capping turned those 400s into
200s.

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
(cherry picked from commit 71dffc1e9a)

litellm/llms/anthropic/experimental_pass_through/messages/transformation.py

@@ -386,6 +386,36 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             return thinking
         return {**thinking, "budget_tokens": max_tokens - 1}
 
+    @staticmethod
+    def _drop_incompatible_temperature_for_thinking(
+        model: str, optional_params: dict, custom_llm_provider: str
+    ) -> None:
+        """Anthropic rejects any ``temperature`` other than 1 while extended thinking
+        is enabled ("temperature may only be set to 1 when thinking is enabled").
+
+        Clients like Claude Code send ``thinking``/``output_config.effort`` together
+        with a pinned ``temperature`` (e.g. the safety classifier uses ``temperature=0``
+        for determinism). When the request lands on a non-adaptive model, the effort
+        interface is reshaped above into legacy ``thinking={type: enabled}`` (or kept
+        as ``output_config.effort`` on Opus 4.5), and the leftover ``temperature`` would
+        400. Preserving the thinking the caller asked for wins over an unhonorable
+        sampling value (Anthropic forces ``temperature=1`` under thinking regardless),
+        so drop it and let the API default apply.
+
+        Adaptive models (4.6+) own this natively and are left untouched.
+        """
+        if AnthropicModelInfo._is_adaptive_thinking_model(model, custom_llm_provider):
+            return
+        temperature = optional_params.get("temperature")
+        if temperature is None or temperature == 1:
+            return
+        thinking = optional_params.get("thinking")
+        output_config = optional_params.get("output_config")
+        thinking_enabled = isinstance(thinking, dict) and thinking.get("type") == "enabled"
+        effort_enabled = isinstance(output_config, dict) and output_config.get("effort") is not None
+        if thinking_enabled or effort_enabled:
+            optional_params.pop("temperature", None)
+
     def transform_anthropic_messages_request(
         self,
         model: str,
@@ -426,6 +456,12 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             custom_llm_provider=self._resolved_provider,
         )
 
+        self._drop_incompatible_temperature_for_thinking(
+            model=model,
+            optional_params=anthropic_messages_optional_request_params,
+            custom_llm_provider=self._resolved_provider,
+        )
+
         system_param = anthropic_messages_optional_request_params.get("system")
         if self.should_strip_billing_metadata() and system_param is not None:
             filtered_system = self._filter_billing_headers_from_system(system_param)

tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_messages_effort.py

@@ -2,6 +2,7 @@ import pytest
 
 from litellm.constants import (
     DEFAULT_REASONING_EFFORT_HIGH_THINKING_BUDGET,
+    DEFAULT_REASONING_EFFORT_LOW_THINKING_BUDGET,
     DEFAULT_REASONING_EFFORT_MEDIUM_THINKING_BUDGET,
     DEFAULT_REASONING_EFFORT_XHIGH_THINKING_BUDGET,
 )
@@ -174,6 +175,81 @@ def test_unrecognized_effort_raises_clean_400():
     assert exc_info.value.status_code == 400
 
 
+def test_pinned_temperature_dropped_when_adaptive_downgraded_to_enabled():
+    """Regression (#33203): Claude Code's safety classifier sends adaptive thinking +
+    temperature=0 to Haiku 4.5. The adaptive interface is downgraded to legacy enabled
+    thinking, but Anthropic rejects "temperature may only be set to 1 when thinking is
+    enabled". The pinned temperature must be dropped so the request succeeds while the
+    downgraded thinking is preserved."""
+    params = _claude_code_payload(effort="medium")
+    params["temperature"] = 0
+    result = _transform("claude-haiku-4-5", params)
+
+    assert result["thinking"] == {
+        "type": "enabled",
+        "budget_tokens": DEFAULT_REASONING_EFFORT_MEDIUM_THINKING_BUDGET,
+    }
+    assert "temperature" not in result
+
+
+def test_temperature_one_preserved_with_enabled_thinking():
+    """temperature=1 is compatible with extended thinking, so it must be kept."""
+    params = _claude_code_payload(effort="medium")
+    params["temperature"] = 1
+    result = _transform("claude-haiku-4-5", params)
+
+    assert result["thinking"]["type"] == "enabled"
+    assert result["temperature"] == 1
+
+
+def test_pinned_temperature_preserved_when_thinking_dropped():
+    """When thinking is dropped entirely (non-reasoning model), there is no thinking
+    conflict, so a pinned temperature must survive untouched."""
+    params = _claude_code_payload(effort="medium")
+    params["temperature"] = 0
+    result = _transform("claude-3-5-haiku-latest", params)
+
+    assert "thinking" not in result
+    assert result["temperature"] == 0
+
+
+def test_pinned_temperature_preserved_for_adaptive_model():
+    """Adaptive models (4.6+) own the thinking/temperature relationship natively, so
+    the passthrough must not strip a pinned temperature for them."""
+    params = _claude_code_payload(effort="high")
+    params["temperature"] = 0
+    result = _transform("claude-sonnet-4-6", params)
+
+    assert result["thinking"] == {"type": "adaptive"}
+    assert result["temperature"] == 0
+
+
+def test_pinned_temperature_dropped_for_opus_4_5_effort():
+    """Opus 4.5 keeps native output_config.effort (extended thinking), which is equally
+    incompatible with a pinned non-1 temperature, so the temperature must be dropped."""
+    params = _claude_code_payload(effort="medium")
+    params["temperature"] = 0
+    result = _transform("claude-opus-4-5", params)
+
+    assert result["output_config"] == {"effort": "medium"}
+    assert "temperature" not in result
+
+
+def test_reasoning_effort_with_pinned_temperature_drops_temperature():
+    """The reasoning_effort alias synthesizes legacy enabled thinking on a non-adaptive
+    model; a co-pinned non-1 temperature must be dropped to avoid the Anthropic 400."""
+    result = _transform(
+        "claude-haiku-4-5",
+        {"max_tokens": 8192, "reasoning_effort": "low", "temperature": 0},
+    )
+
+    assert result["thinking"] == {
+        "type": "enabled",
+        "budget_tokens": DEFAULT_REASONING_EFFORT_LOW_THINKING_BUDGET,
+    }
+    assert "temperature" not in result
+
+
 def test_non_adaptive_request_without_effort_is_untouched():
     """A non-adaptive model receiving a request with no adaptive interface (no
     effort, no adaptive thinking) must pass through untouched."""