fix(azure_ai): bridge Foundry function-tool requests only where the chat surface rejects them

Foundry's OpenAI v1 chat surface rejects function tools with an explicit
reasoning_effort from gpt-5.6 on and with reasoning left on from gpt-6 on,
while gpt-5.4, gpt-5.5 and unset-effort gpt-5.6 serve them. Key the
azure_ai bridge on those measured boundaries instead of the azure
provider's gpt-5.4+ rule so working chat traffic keeps its n, logprobs,
seed and chatcmpl ids.

litellm/llms/azure_ai/common_utils.py

@@ -6,6 +6,7 @@ from urllib.parse import urlparse
 
 import litellm
 from litellm.llms.base_llm.base_utils import BaseLLMModelInfo, BaseTokenCounter
+from litellm.llms.openai.chat.gpt_5_transformation import OpenAIGPT5Config
 from litellm.secret_managers.main import get_secret_str
 from litellm.types.llms.openai import AllMessageValues
 from litellm.types.router import GenericLiteLLMParams
@@ -150,6 +151,14 @@ def azure_ai_supports_native_responses(model: str | None, api_base: str | None)
     return AzureFoundryModelInfo.get_azure_ai_route(model) == "default"
 
 
+def foundry_chat_rejects_function_tools_while_reasoning(
+    model: str, reasoning_effort: str | Mapping[str, object] | None
+) -> bool:
+    if reasoning_effort is None:
+        return OpenAIGPT5Config.is_model_gpt_6_plus_model(model)
+    return OpenAIGPT5Config.is_model_gpt_5_6_plus_model(model)
+
+
 class AzureFoundryModelInfo(BaseLLMModelInfo):
     """Model info for Azure AI / Azure Foundry models."""
 

litellm/llms/openai/chat/gpt_5_transformation.py

@@ -1,5 +1,6 @@
 """Support for OpenAI gpt-5 model family."""
 
+import re
 from typing import Final
 
 import litellm
@@ -11,6 +12,8 @@ from litellm.utils import (
 
 from .gpt_transformation import OpenAIGPTConfig
 
+_GPT_SERIES_VERSION: Final = re.compile(r"^gpt-(\d+)(?:\.(\d+))?(?=[.-]|$)")
+
 
 def _catalogue_declares_default_effort() -> bool:
     """Whether the loaded cost map carries default_reasoning_effort for ANY entry.
@@ -112,20 +115,28 @@ class OpenAIGPT5Config(OpenAIGPTConfig):
         model_name: Final = model.split("/")[-1]
         return model_name.startswith("gpt-5.4")
 
+    @staticmethod
+    def _gpt_series_version(model: str) -> tuple[int, int] | None:
+        match: Final = _GPT_SERIES_VERSION.match(model.split("/")[-1])
+        if match is None:
+            return None
+        return int(match.group(1)), int(match.group(2) or 0)
+
     @classmethod
     def is_model_gpt_5_4_plus_model(cls, model: str) -> bool:
         """Check if the model is gpt-5.4 or newer (5.4, 5.5, 5.6, etc., including pro)."""
-        model_name: Final = model.split("/")[-1]
-        if model_name.startswith("gpt-6"):
-            return True
-        if not model_name.startswith("gpt-5."):
-            return False
-        try:
-            version_str: Final = model_name.replace("gpt-5.", "").split("-")[0]
-            major: Final = version_str.split(".")[0]
-            return int(major) >= 4
-        except (ValueError, IndexError):
-            return False
+        version: Final = cls._gpt_series_version(model)
+        return version is not None and version >= (5, 4)
+
+    @classmethod
+    def is_model_gpt_5_6_plus_model(cls, model: str) -> bool:
+        version: Final = cls._gpt_series_version(model)
+        return version is not None and version >= (5, 6)
+
+    @classmethod
+    def is_model_gpt_6_plus_model(cls, model: str) -> bool:
+        version: Final = cls._gpt_series_version(model)
+        return version is not None and version >= (6, 0)
 
     @classmethod
     def _model_map_lookup_name(cls, model: str) -> str:

litellm/main.py

@@ -100,7 +100,10 @@ from litellm.litellm_core_utils.prompt_templates.common_utils import (
 from litellm.litellm_core_utils.request_timeout_resolver import (
     get_configured_request_timeout,
 )
-from litellm.llms.azure_ai.common_utils import azure_ai_supports_native_responses
+from litellm.llms.azure_ai.common_utils import (
+    azure_ai_supports_native_responses,
+    foundry_chat_rejects_function_tools_while_reasoning,
+)
 from litellm.llms.base_llm import BaseConfig, BaseImageGenerationConfig
 from litellm.llms.base_llm.base_model_iterator import (
     convert_model_response_to_streaming,
@@ -1107,6 +1110,10 @@ def responses_api_bridge_check(
     #   provider with a custom api_base and gpt-5.4+ model names serve tools without
     #   reasoning fine and have no /responses route, so they keep pre-existing
     #   behavior (bridge only on an explicit reasoning_effort).
+    # - Azure AI Foundry's OpenAI v1 hosts (azure_ai provider) enforce it later in the series:
+    #   an explicit effort with function tools is rejected from gpt-5.6 on, and the unset
+    #   effort only from gpt-6 on (gpt-5.6 serves tools with reasoning silently off), so the
+    #   azure_ai gate keys on those measured boundaries instead of gpt-5.4+.
     # - Older GPT-5 names (e.g. ``gpt-5``, ``gpt-5.1``): bridge only when a reasoning
     #   summary alias is present with ``reasoning_effort`` (tools alone stay on chat).
     has_function_tool: Final = any(
@@ -1119,35 +1126,35 @@ def responses_api_bridge_check(
         reasoning_active = reasoning_effort != "none"
     # The reasoning+tools constraint is enforced by the real OpenAI backend behind any api.openai.com
     # host (the default URL or a PrivateLink hostname such as <region>.privatelink.api.openai.com) and
-    # by Azure OpenAI, whether reached through the azure provider or as a Foundry OpenAI v1 host through
-    # the azure_ai provider. Resolve the effective OpenAI base arg>global>env>default exactly as the chat
-    # handler does, so a custom base set via litellm.api_base or OPENAI_BASE_URL/OPENAI_API_BASE isn't
-    # misread as the default and bridged to a /responses route it lacks. A whitespace-only base
-    # collapses to the default too.
+    # by Azure OpenAI through the azure provider. Resolve the effective OpenAI base arg>global>env>default
+    # exactly as the chat handler does, so a custom base set via litellm.api_base or
+    # OPENAI_BASE_URL/OPENAI_API_BASE isn't misread as the default and bridged to a /responses route it
+    # lacks. A whitespace-only base collapses to the default too.
     resolved_api_base: Final = _resolve_openai_api_base(api_base).strip()
     on_foundry_openai_endpoint: Final = custom_llm_provider == "azure_ai" and azure_ai_supports_native_responses(
         model, api_base
     )
     on_constraint_enforcing_endpoint: Final = (
-        custom_llm_provider == "azure"
-        or on_foundry_openai_endpoint
-        or resolved_api_base == ""
-        or _is_openai_backed_api_base(resolved_api_base)
+        custom_llm_provider == "azure" or resolved_api_base == "" or _is_openai_backed_api_base(resolved_api_base)
+    )
+    chat_rejects_function_tools: Final = (
+        has_function_tool
+        and reasoning_active
+        and (
+            foundry_chat_rejects_function_tools_while_reasoning(model, reasoning_effort)
+            if on_foundry_openai_endpoint
+            else (
+                OpenAIGPT5Config.is_model_gpt_5_4_plus_model(model)
+                and (reasoning_effort is not None or on_constraint_enforcing_endpoint)
+            )
+        )
     )
     if (
         (custom_llm_provider in ("openai", "azure") or on_foundry_openai_endpoint)
         and model_info.get("mode") != "responses"
         and OpenAIGPT5Config.is_model_gpt_5_model(model)
         and not OpenAIGPT5Config.is_model_gpt_5_search_model(model)
-        and (
-            (reasoning_effort is not None and reasoning_summary is not None)
-            or (
-                OpenAIGPT5Config.is_model_gpt_5_4_plus_model(model)
-                and has_function_tool
-                and reasoning_active
-                and (reasoning_effort is not None or on_constraint_enforcing_endpoint)
-            )
-        )
+        and ((reasoning_effort is not None and reasoning_summary is not None) or chat_rejects_function_tools)
     ):
         model_info["mode"] = "responses"
         model = model.replace("responses/", "")

tests/test_litellm/llms/openai/test_is_model_gpt_5_model.py

@@ -159,6 +159,58 @@ class TestOpenAIGPT5ConfigIsModelGpt54PlusModel:
         ), f"Expected '{model}' NOT to be classified as gpt-5.4-or-newer"
 
 
+GPT5_6_PLUS_MODELS = [
+    "gpt-6-astra",
+    "openai/gpt-6-astra",
+    "gpt-5.6",
+    "gpt-5.6-sol",
+    "gpt-5.6-terra",
+    "gpt-5.10-preview",
+]
+
+GPT5_PRE_5_6_MODELS = [
+    "gpt-5",
+    "gpt-5.4",
+    "gpt-5.4-mini",
+    "gpt-5.5",
+    "gpt-5.5-pro",
+    "gpt-4o",
+]
+
+GPT6_PLUS_MODELS = [
+    "gpt-6-astra",
+    "openai/gpt-6-astra",
+    "gpt-6",
+    "gpt-6.1-preview",
+]
+
+GPT_PRE_6_MODELS = [
+    "gpt-5.6-sol",
+    "gpt-5.5",
+    "gpt-5",
+    "gpt-4o",
+]
+
+
+class TestOpenAIGPT5ConfigSeriesBoundaries:
+
+    @pytest.mark.parametrize("model", GPT5_6_PLUS_MODELS)
+    def test_gpt5_6_plus_models_are_classified_as_5_6_plus(self, model: str):
+        assert OpenAIGPT5Config.is_model_gpt_5_6_plus_model(model)
+
+    @pytest.mark.parametrize("model", GPT5_PRE_5_6_MODELS)
+    def test_pre_5_6_models_are_not_classified_as_5_6_plus(self, model: str):
+        assert not OpenAIGPT5Config.is_model_gpt_5_6_plus_model(model)
+
+    @pytest.mark.parametrize("model", GPT6_PLUS_MODELS)
+    def test_gpt6_plus_models_are_classified_as_6_plus(self, model: str):
+        assert OpenAIGPT5Config.is_model_gpt_6_plus_model(model)
+
+    @pytest.mark.parametrize("model", GPT_PRE_6_MODELS)
+    def test_pre_6_models_are_not_classified_as_6_plus(self, model: str):
+        assert not OpenAIGPT5Config.is_model_gpt_6_plus_model(model)
+
+
 # ---------------------------------------------------------------------------
 # AzureOpenAIGPT5Config
 # ---------------------------------------------------------------------------

tests/test_litellm/test_main.py

@@ -1313,25 +1313,29 @@ _FOUNDRY_FUNCTION_TOOL: Final = ({"type": "function", "function": {"name": "get_
 
 
 @pytest.mark.parametrize(
-    "api_base, reasoning_effort",
+    "model_name, api_base, reasoning_effort",
     [
-        pytest.param(_FOUNDRY_API_BASE, None, id="foundry-host-unset-effort"),
-        pytest.param(_FOUNDRY_API_BASE, "low", id="foundry-host-explicit-effort"),
-        pytest.param("https://myresource.openai.azure.com", None, id="azure-openai-host-unset-effort"),
+        pytest.param("gpt-6-astra", _FOUNDRY_API_BASE, None, id="gpt-6-unset-effort"),
+        pytest.param("gpt-6-astra", _FOUNDRY_API_BASE, "low", id="gpt-6-explicit-effort"),
+        pytest.param("gpt-6-astra", "https://myresource.openai.azure.com", None, id="gpt-6-azure-openai-host"),
+        pytest.param("gpt-5.6-sol", _FOUNDRY_API_BASE, "low", id="gpt-5.6-explicit-effort"),
+        pytest.param("gpt-5.6-sol", _FOUNDRY_API_BASE, {"effort": "high"}, id="gpt-5.6-explicit-effort-dict"),
     ],
 )
-def test_responses_api_bridge_check_azure_ai_foundry_gpt_5_4_plus_tools_routes_to_responses(api_base, reasoning_effort):
+def test_responses_api_bridge_check_azure_ai_foundry_rejected_tools_route_to_responses(
+    model_name, api_base, reasoning_effort
+):
     from litellm.main import responses_api_bridge_check
 
     model_info, model = responses_api_bridge_check(
-        model="gpt-6-astra",
+        model=model_name,
         custom_llm_provider="azure_ai",
         tools=_FOUNDRY_FUNCTION_TOOL,
         reasoning_effort=reasoning_effort,
         api_base=api_base,
     )
 
-    assert model == "gpt-6-astra"
+    assert model == model_name
     assert model_info.get("mode") == "responses"
 
 
@@ -1339,6 +1343,11 @@ def test_responses_api_bridge_check_azure_ai_foundry_gpt_5_4_plus_tools_routes_t
     "model_name, api_base, reasoning_effort",
     [
         pytest.param("gpt-6-astra", _FOUNDRY_API_BASE, "none", id="explicit-none-stays-chat"),
+        pytest.param("gpt-5.6-sol", _FOUNDRY_API_BASE, None, id="gpt-5.6-unset-effort-stays-chat"),
+        pytest.param("gpt-5.6-sol", _FOUNDRY_API_BASE, "none", id="gpt-5.6-explicit-none-stays-chat"),
+        pytest.param("gpt-5.5", _FOUNDRY_API_BASE, "high", id="gpt-5.5-explicit-effort-stays-chat"),
+        pytest.param("gpt-5.4-mini", _FOUNDRY_API_BASE, None, id="gpt-5.4-mini-unset-effort-stays-chat"),
+        pytest.param("gpt-5.4-mini", _FOUNDRY_API_BASE, "low", id="gpt-5.4-mini-explicit-effort-stays-chat"),
         pytest.param("gpt-6-astra", "https://myproject.models.ai.azure.com", None, id="serverless-host-stays-chat"),
         pytest.param("Mistral-large-2411", _FOUNDRY_API_BASE, None, id="non-gpt-5-model-stays-chat"),
         pytest.param("claude-opus-4-1", _FOUNDRY_API_BASE, None, id="claude-on-foundry-stays-chat"),