fix: keep reasoning_effort xhigh on Gemini and suffixed Claude ids

Gemini has no thinking level above high, so xhigh was a 400. Claude ids with an effort suffix such as claude-sonnet-5-5-high now inherit the base model's xhigh flag.

litellm/llms/anthropic/common_utils.py

@@ -108,6 +108,7 @@ def anthropic_error_frame_exception(error_type: str, message: str, status_code:
 _BEDROCK_VERSION_SUFFIX_RE: Final = re.compile(r"-v\d+(?::\d+)?$")
 _INFERENCE_PROFILE_MINOR_RE: Final = re.compile(r":\d+$")
 _DATED_RELEASE_SUFFIX_RE: Final = re.compile(r"-\d{8}$")
+_EFFORT_ALIAS_SUFFIX_RE: Final = re.compile(r"-(?:minimal|low|medium|high|xhigh|max)$")
 _DOTTED_VERSION_RE: Final = re.compile(r"(\d)\.(\d)")
 _CLAUDE_CODE_BILLING_HEADER_PREFIX: Final = "x-anthropic-billing-header:"
 OBJECT_MAPPING_ADAPTER: Final = TypeAdapter(dict[object, object])
@@ -743,7 +744,9 @@ class AnthropicModelInfo(BaseLLMModelInfo):
         (``4.6`` -> ``4-6``). Lets any reasonable alias (e.g.
         ``bedrock/invoke/global.anthropic.claude-opus-4-7-v1:0``,
         ``claude-sonnet-4-6-20260219`` or ``claude-sonnet-4.6``) resolve to its base
-        cost-map entry so the capability flag on that entry stays authoritative."""
+        cost-map entry so the capability flag on that entry stays authoritative.
+        A trailing effort alias (``-high``, ``-xhigh``) is tried the same way, so
+        ``claude-sonnet-5-5-high`` keeps the xhigh flag from ``claude-sonnet-5-5``."""
         prefixes: Final = (
             "bedrock/converse/",
             "bedrock/invoke/",
@@ -766,6 +769,7 @@ class AnthropicModelInfo(BaseLLMModelInfo):
                 _BEDROCK_VERSION_SUFFIX_RE.sub("", cand),
                 _INFERENCE_PROFILE_MINOR_RE.sub("", cand),
                 _DATED_RELEASE_SUFFIX_RE.sub("", cand),
+                _EFFORT_ALIAS_SUFFIX_RE.sub("", cand),
                 _DOTTED_VERSION_RE.sub(r"\1-\2", cand),
                 _strip_bedrock_id_suffixes(cand),
                 AnthropicModelInfo._strip_version_suffix(cand),

litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py

@@ -985,7 +985,8 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
                 "thinkingBudget": DEFAULT_REASONING_EFFORT_MEDIUM_THINKING_BUDGET,
                 "includeThoughts": sends_thoughts,
             }
-        elif reasoning_effort == "high":
+        elif reasoning_effort in ("high", "xhigh"):
+            # Gemini has no thinking budget above high. OpenAI clients send xhigh.
             return {
                 "thinkingBudget": DEFAULT_REASONING_EFFORT_HIGH_THINKING_BUDGET,
                 "includeThoughts": sends_thoughts,
@@ -1037,7 +1038,8 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
             return {"thinkingLevel": "low", "includeThoughts": sends_thoughts}
         elif reasoning_effort == "medium":
             return {"thinkingLevel": "medium", "includeThoughts": sends_thoughts}
-        elif reasoning_effort == "high":
+        elif reasoning_effort in ("high", "xhigh"):
+            # Gemini 3+ thinkingLevel tops out at high. Keep xhigh instead of 400.
             return {"thinkingLevel": "high", "includeThoughts": sends_thoughts}
         elif reasoning_effort in ("disable", "none"):
             return {

tests/unit/llms/anthropic/chat/test_anthropic_chat_transformation.py

@@ -2640,6 +2640,12 @@ def test_supports_effort_level_handles_provider_prefixes(model, level, expected)
     assert AnthropicConfig._supports_effort_level(model, level, "anthropic") is expected
 
 
+def test_effort_alias_suffix_inherits_base_model_xhigh():
+    """``claude-sonnet-5-5-high`` is the same model as ``claude-sonnet-5-5``."""
+    assert AnthropicConfig._supports_effort_level("claude-sonnet-5-5-high", "xhigh", "anthropic") is True
+    assert AnthropicConfig.validate_effort_for_model("claude-sonnet-5-5-high", "xhigh", "anthropic") is None
+
+
 @pytest.mark.parametrize(
     "model,effort,expect_error",
     [

tests/unit/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py

@@ -3285,6 +3285,22 @@ def test_reasoning_effort_maps_to_thinking_level_gemini_3():
     assert result["thinkingConfig"]["thinkingLevel"] == "high"
     assert result["thinkingConfig"]["includeThoughts"] is True
 
+    # xhigh has no Gemini thinkingLevel above high, so it uses that ceiling.
+    optional_params = {}
+    non_default_params = {"reasoning_effort": "xhigh"}
+    result = v.map_openai_params(
+        non_default_params=non_default_params,
+        optional_params=optional_params,
+        model=model,
+        drop_params=False,
+    )
+    assert result["thinkingConfig"]["thinkingLevel"] == "high"
+    assert result["thinkingConfig"]["includeThoughts"] is True
+    assert (
+        VertexGeminiConfig._map_reasoning_effort_to_thinking_budget("xhigh", "gemini-2.5-pro")
+        == VertexGeminiConfig._map_reasoning_effort_to_thinking_budget("high", "gemini-2.5-pro")
+    )
+
     # Test disable -> low + includeThoughts=False (cannot fully disable in Gemini 3)
     optional_params = {}
     non_default_params = {"reasoning_effort": "disable"}