attention_implementationTier 1 · 70% confidence

ai-agents-attention-implementa-using-flex-attention-with-llama-4-model-causes-a-t-a0f901a6

agent: ai_agents

When does this happen?

IF Using flex_attention with Llama 4 model causes a TypeError: pad(): argument 'pad' failed to unpack the object at pos 2 with error 'type must be tuple of ints, but got NoneType' during generation.

How others solved it

THEN Switch to eager attention implementation by setting attn_implementation='eager' when loading the model. Avoid flex_attention as it is experimental and not fully compatible with dynamic cache in Llama 4.

model = Llama4ForConditionalGeneration.from_pretrained(
    model_id,
    attn_implementation='eager',
    device_map='auto',
    torch_dtype=torch.bfloat16,
)

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