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Fix GPT-OSS BlockMask error during inference #3982

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Merged
danielhanchen merged 1 commit into from
Feb 5, 2026
Merged

Fix GPT-OSS BlockMask error during inference #3982

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6 changes: 6 additions & 0 deletions unsloth/models/_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,12 @@ def prefer_flex_attn_if_supported(model_class, config):
model_class, "_supports_flex_attn", False
):
return None
# GPT-OSS uses eager attention during inference since flex attention
# returns incorrect results (likely due to left padding issues).
# Skip setting flex_attention to avoid BlockMask type errors.
model_type = getattr(config, "model_type", "") if config else ""
if model_type == "gpt_oss":
return None
if config is not None:
setattr(config, "_attn_implementation", "flex_attention")
if hasattr(config, "attn_implementation"):
Expand Down