diff --git a/nanobot/providers/openai_compat_provider.py b/nanobot/providers/openai_compat_provider.py
index 5b766edf6..3a2ba2fbe 100644
--- a/nanobot/providers/openai_compat_provider.py
+++ b/nanobot/providers/openai_compat_provider.py
@@ -94,10 +94,10 @@ def _model_slug(model_name: str) -> str:
 
 
 def _requires_max_completion_tokens(model_name: str) -> bool:
-    """Return True for models that reject ``max_tokens`` (GPT-5 family, o3/o4)."""
+    """Return True for models that reject ``max_tokens`` (GPT-5 family, o-series)."""
     slug = _model_slug(model_name)
     return "gpt-5" in slug or any(
-        slug == p or slug.startswith((p + "-", p + ".")) for p in ("o3", "o4")
+        slug == p or slug.startswith((p + "-", p + ".")) for p in ("o1", "o3", "o4")
     )
 
 
diff --git a/tests/providers/test_litellm_kwargs.py b/tests/providers/test_litellm_kwargs.py
index 81e5f5d0a..27896e58b 100644
--- a/tests/providers/test_litellm_kwargs.py
+++ b/tests/providers/test_litellm_kwargs.py
@@ -933,8 +933,12 @@ def test_openai_compat_build_kwargs_uses_gpt5_safe_parameters() -> None:
     ("model_name", "expected_key"),
     [
         ("gpt-5.4", "max_completion_tokens"),
+        ("o1-mini", "max_completion_tokens"),
         ("o3-mini", "max_completion_tokens"),
+        ("o4-mini", "max_completion_tokens"),
         ("gpt-4", "max_tokens"),
+        ("foo3-mini", "max_tokens"),
+        ("foo4-mini", "max_tokens"),
     ],
 )
 def test_openai_compat_build_kwargs_max_completion_tokens_by_model_name(