test: add gpt-5.5 coverage for model cost map and gpt-5 routing

- Add gpt-5.5 to GPT5_MODELS parametrized list so both OpenAIGPT5Config
  and AzureOpenAIGPT5Config routing tests cover the new model.
- Add test_generic_cost_per_token_gpt55 verifying the new entry's
  cost-map values ($5/$0.50/$30 per 1M) and that generic_cost_per_token
  returns the expected prompt/completion costs.

tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py

@@ -328,6 +328,43 @@ def test_generic_cost_per_token_gpt54_above_272k_tokens():
     assert round(completion_cost, 10) == round(expected_completion, 10)
 
 
+def test_generic_cost_per_token_gpt55():
+    """gpt-5.5: base pricing — $5/1M input, $30/1M output, $0.50/1M cached input."""
+    model = "gpt-5.5"
+    custom_llm_provider = "openai"
+    os.environ["LITELLM_LOCAL_MODEL_COST_MAP"] = "True"
+    litellm.model_cost = litellm.get_model_cost_map(url="")
+
+    model_cost_map = litellm.model_cost[model]
+
+    # Sanity-check the map values match OpenAI's published pricing.
+    assert model_cost_map["input_cost_per_token"] == 5e-6
+    assert model_cost_map["output_cost_per_token"] == 3e-5
+    assert model_cost_map["cache_read_input_token_cost"] == 5e-7
+    assert model_cost_map["litellm_provider"] == "openai"
+    assert model_cost_map["mode"] == "chat"
+    assert model_cost_map["max_input_tokens"] == 272000
+
+    prompt_tokens = 1000
+    completion_tokens = 500
+    usage = Usage(
+        prompt_tokens=prompt_tokens,
+        completion_tokens=completion_tokens,
+        total_tokens=prompt_tokens + completion_tokens,
+    )
+    prompt_cost, completion_cost = generic_cost_per_token(
+        model=model,
+        usage=usage,
+        custom_llm_provider=custom_llm_provider,
+    )
+    assert round(prompt_cost, 10) == round(
+        model_cost_map["input_cost_per_token"] * prompt_tokens, 10
+    )
+    assert round(completion_cost, 10) == round(
+        model_cost_map["output_cost_per_token"] * completion_tokens, 10
+    )
+
+
 def test_generic_cost_per_token_anthropic_prompt_caching():
     model = "claude-sonnet-4@20250514"
     usage = Usage(

tests/test_litellm/llms/openai/test_is_model_gpt_5_model.py

@@ -0,0 +1,152 @@
+"""
+Regression tests for is_model_gpt_5_model() in both OpenAI and Azure GPT-5 config
+classes.
+
+Background
+----------
+In v1.82.3 a substring check was introduced::
+
+    return "gpt-5" in model and "gpt-5-chat" not in model
+
+This inadvertently treated versioned chat models like ``gpt-5.3-chat`` and
+``gpt-5.1-chat`` as *non*-GPT-5 models, because the string ``"gpt-5-chat"`` is
+a substring of ``"gpt-5.3-chat"``.  Those models were then routed through the
+regular Azure chat path which does not suppress ``parallel_tool_calls``, causing
+Azure to return ``finish_reason="stop"`` together with tool_calls and breaking
+n8n AI-agent workflows.
+
+There are two distinct families:
+
+* **gpt-5-chat family** (``gpt-5-chat``, ``gpt-5-chat-latest``,
+  ``gpt-5-chat-2025-08-07``, …) — regular chat models that support ``temperature``
+  and ``tool_choice`` but NOT ``reasoning_effort``.  Must NOT be on the GPT-5
+  reasoning path.
+
+* **Versioned chat models** (``gpt-5.1-chat``, ``gpt-5.2-chat``,
+  ``gpt-5.3-chat``, …) — ARE GPT-5 reasoning models and must stay on the GPT-5
+  path.
+
+The fix uses a prefix check (``startswith("gpt-5-chat")``) on the normalised model
+name instead of a substring check, which correctly distinguishes the two families.
+"""
+
+import pytest
+
+from litellm.llms.openai.chat.gpt_5_transformation import OpenAIGPT5Config
+from litellm.llms.azure.chat.gpt_5_transformation import AzureOpenAIGPT5Config
+
+# ---------------------------------------------------------------------------
+# Parametrized fixtures
+# ---------------------------------------------------------------------------
+
+# Models that MUST be classified as GPT-5 (routed through GPT-5 reasoning path)
+GPT5_MODELS = [
+    "gpt-5",
+    "gpt-5.1",
+    "gpt-5.2",
+    "gpt-5.3",
+    "gpt-5.4",
+    "gpt-5.5",
+    "gpt-5.1-chat",  # versioned chat — THE KEY REGRESSION CASE
+    "gpt-5.2-chat",  # versioned chat — also a regression case
+    "gpt-5.3-chat",  # versioned chat — THE KEY REGRESSION CASE
+    "gpt-5.2-chat-latest",  # versioned chat with date suffix
+    "gpt-5.1-codex",
+    "gpt-5.1-codex-mini",
+    "gpt-5.1-mini",
+    "gpt-5-nano",
+    "gpt-5-mini",
+    "gpt-5-codex",
+]
+
+# Models that must NOT be classified as GPT-5 (regular chat path)
+NON_GPT5_MODELS = [
+    "gpt-5-chat",  # gpt-5-chat family — regular chat path
+    "gpt-5-chat-latest",  # gpt-5-chat family with alias suffix
+    "gpt-5-chat-2025-08-07",  # gpt-5-chat family with date suffix
+    "gpt-4",
+    "gpt-4o",
+    "gpt-4-turbo",
+    "gpt-3.5-turbo",
+    "o1",
+    "o3",
+    "o3-mini",
+]
+
+
+# ---------------------------------------------------------------------------
+# OpenAIGPT5Config
+# ---------------------------------------------------------------------------
+
+
+class TestOpenAIGPT5ConfigIsModelGpt5Model:
+
+    @pytest.mark.parametrize("model", GPT5_MODELS)
+    def test_gpt5_models_are_classified_as_gpt5(self, model: str):
+        assert OpenAIGPT5Config.is_model_gpt_5_model(
+            model
+        ), f"Expected '{model}' to be classified as a GPT-5 model"
+
+    @pytest.mark.parametrize("model", NON_GPT5_MODELS)
+    def test_non_gpt5_models_are_not_classified_as_gpt5(self, model: str):
+        assert not OpenAIGPT5Config.is_model_gpt_5_model(
+            model
+        ), f"Expected '{model}' NOT to be classified as a GPT-5 model"
+
+    def test_versioned_chat_models_are_not_excluded_by_prefix(self):
+        """Core regression guard: gpt-5-chat prefix must not match versioned models."""
+        versioned_chat_models = ["gpt-5.1-chat", "gpt-5.2-chat", "gpt-5.3-chat"]
+        for model in versioned_chat_models:
+            assert OpenAIGPT5Config.is_model_gpt_5_model(
+                model
+            ), f"Regression: '{model}' was incorrectly excluded from GPT-5 path"
+
+    def test_gpt5_chat_family_is_excluded(self):
+        """gpt-5-chat family should stay on the regular chat path."""
+        for model in ["gpt-5-chat", "gpt-5-chat-latest", "gpt-5-chat-2025-08-07"]:
+            assert not OpenAIGPT5Config.is_model_gpt_5_model(
+                model
+            ), f"Expected '{model}' (gpt-5-chat family) NOT to be on the GPT-5 path"
+
+
+# ---------------------------------------------------------------------------
+# AzureOpenAIGPT5Config
+# ---------------------------------------------------------------------------
+
+
+class TestAzureOpenAIGPT5ConfigIsModelGpt5Model:
+
+    @pytest.mark.parametrize("model", GPT5_MODELS)
+    def test_gpt5_models_are_classified_as_gpt5(self, model: str):
+        assert AzureOpenAIGPT5Config.is_model_gpt_5_model(
+            model
+        ), f"Expected Azure '{model}' to be classified as a GPT-5 model"
+
+    @pytest.mark.parametrize("model", NON_GPT5_MODELS)
+    def test_non_gpt5_models_are_not_classified_as_gpt5(self, model: str):
+        assert not AzureOpenAIGPT5Config.is_model_gpt_5_model(
+            model
+        ), f"Expected Azure '{model}' NOT to be classified as a GPT-5 model"
+
+    def test_versioned_chat_models_are_not_excluded_by_prefix(self):
+        """Core regression guard: gpt-5-chat prefix must not match versioned models."""
+        versioned_chat_models = ["gpt-5.1-chat", "gpt-5.2-chat", "gpt-5.3-chat"]
+        for model in versioned_chat_models:
+            assert AzureOpenAIGPT5Config.is_model_gpt_5_model(
+                model
+            ), f"Regression: Azure '{model}' was incorrectly excluded from GPT-5 path"
+
+    def test_gpt5_chat_family_is_excluded(self):
+        """gpt-5-chat family should stay on the regular chat path."""
+        for model in ["gpt-5-chat", "gpt-5-chat-latest", "gpt-5-chat-2025-08-07"]:
+            assert not AzureOpenAIGPT5Config.is_model_gpt_5_model(
+                model
+            ), f"Expected Azure '{model}' (gpt-5-chat family) NOT to be on the GPT-5 path"
+
+    def test_gpt5_series_routing_prefix_is_always_classified_as_gpt5(self):
+        """Models using the gpt5_series/ manual-routing prefix must always match."""
+        series_models = ["gpt5_series/my-deployment", "gpt5_series/prod"]
+        for model in series_models:
+            assert AzureOpenAIGPT5Config.is_model_gpt_5_model(
+                model
+            ), f"Azure '{model}' with gpt5_series/ prefix should be classified as GPT-5"