openai[patch]: update system role to developer for o-series models (#29785)

Some o-series models will raise a 400 error for `"role": "system"`
(`o1-mini` and `o1-preview` will raise, `o1` and `o3-mini` will not).

Here we update `ChatOpenAI` to update the role to `"developer"` for all
model names matching `^o\d`.

We only make this change on the ChatOpenAI class (not BaseChatOpenAI).

libs/partners/openai/langchain_openai/chat_models/base.py

@@ -6,6 +6,7 @@ import base64
 import json
 import logging
 import os
+import re
 import sys
 import warnings
 from io import BytesIO
@@ -2011,6 +2012,12 @@ class ChatOpenAI(BaseChatOpenAI):  # type: ignore[override]
         # in September 2024 release
         if "max_tokens" in payload:
             payload["max_completion_tokens"] = payload.pop("max_tokens")
+
+        # Mutate system message role to "developer" for o-series models
+        if self.model_name and re.match(r"^o\d", self.model_name):
+            for message in payload.get("messages", []):
+                if message["role"] == "system":
+                    message["role"] = "developer"
         return payload
 
     def _should_stream_usage(

libs/partners/openai/tests/unit_tests/chat_models/test_base.py

@@ -881,6 +881,20 @@ def test__get_request_payload() -> None:
     payload = llm._get_request_payload(messages)
     assert payload == expected
 
+    # Test we coerce to developer role for o-series models
+    llm = ChatOpenAI(model="o3-mini")
+    payload = llm._get_request_payload(messages)
+    expected = {
+        "messages": [
+            {"role": "developer", "content": "hello"},
+            {"role": "developer", "content": "bye"},
+            {"role": "user", "content": "how are you"},
+        ],
+        "model": "o3-mini",
+        "stream": False,
+    }
+    assert payload == expected
+
 
 def test_init_o1() -> None:
     with pytest.warns(None) as record:  # type: ignore[call-overload]