diff --git a/dspy/clients/lm.py b/dspy/clients/lm.py
index 19085bea81..c165ceca4d 100644
--- a/dspy/clients/lm.py
+++ b/dspy/clients/lm.py
@@ -85,7 +85,13 @@ def __init__(
         model_family = model.split("/")[-1].lower() if "/" in model else model.lower()
 
         # Recognize OpenAI reasoning models (o1, o3, o4, gpt-5 family)
-        model_pattern = re.match(r"^(?:o[1345]|gpt-5)(?:-(?:mini|nano))?", model_family)
+        # Exclude non-reasoning variants like gpt-5-chat this is in azure ai foundry
+        # Allow date suffixes like -2023-01-01 after model name or mini/nano/pro
+        # For gpt-5, use negative lookahead to exclude -chat and allow other suffixes
+        model_pattern = re.match(
+            r"^(?:o[1345](?:-(?:mini|nano|pro))?(?:-\d{4}-\d{2}-\d{2})?|gpt-5(?!-chat)(?:-.*)?)$",
+            model_family,
+        )
 
         if model_pattern:
             if (temperature and temperature != 1.0) or (max_tokens and max_tokens < 16000):
diff --git a/tests/clients/test_lm.py b/tests/clients/test_lm.py
index a24c09a9d4..64e76ecd9c 100644
--- a/tests/clients/test_lm.py
+++ b/tests/clients/test_lm.py
@@ -298,6 +298,7 @@ def test_reasoning_model_token_parameter():
         ("openai/gpt-5", True),
         ("openai/gpt-5-mini", True),
         ("openai/gpt-5-nano", True),
+        ("azure/gpt-5-chat", False),  # gpt-5-chat is NOT a reasoning model
         ("openai/gpt-4", False),
         ("anthropic/claude-2", False),
     ]
@@ -318,7 +319,7 @@ def test_reasoning_model_token_parameter():
             assert lm.kwargs["max_tokens"] == 1000
 
 
-@pytest.mark.parametrize("model_name", ["openai/o1", "openai/gpt-5-nano"])
+@pytest.mark.parametrize("model_name", ["openai/o1", "openai/gpt-5-nano", "openai/gpt-5-mini"])
 def test_reasoning_model_requirements(model_name):
     # Should raise assertion error if temperature or max_tokens requirements not met
     with pytest.raises(
@@ -347,6 +348,21 @@ def test_reasoning_model_requirements(model_name):
     assert lm.kwargs["max_completion_tokens"] is None
 
 
+def test_gpt_5_chat_not_reasoning_model():
+    """Test that gpt-5-chat is NOT treated as a reasoning model."""
+    # Should NOT raise validation error - gpt-5-chat is not a reasoning model
+    lm = dspy.LM(
+        model="openai/gpt-5-chat",
+        temperature=0.7,  # Can be any value
+        max_tokens=1000,  # Can be any value
+    )
+    # Should use max_tokens, not max_completion_tokens
+    assert "max_completion_tokens" not in lm.kwargs
+    assert "max_tokens" in lm.kwargs
+    assert lm.kwargs["max_tokens"] == 1000
+    assert lm.kwargs["temperature"] == 0.7
+
+
 def test_dump_state():
     lm = dspy.LM(
         model="openai/gpt-4o-mini",