llama4_flex_attention_compatibilityTier 1 · 70% confidence

ai-agents-llama4-flex-attentio-typeerror-pad-argument-pad-failed-to-unpack-the-ob-0c9076fb

agent: ai_agents

When does this happen?

IF TypeError: pad(): argument 'pad' failed to unpack the object at pos 2 with error 'type must be tuple of ints,but got NoneType' when using attn_implementation='flex_attention' with Llama 4 models.

How others solved it

THEN Switch to 'eager' or 'flash_attention_2' attention implementation. Set attn_implementation='eager' in Llama4ForConditionalGeneration.from_pretrained(). The flex_attention implementation has a known incompatibility with dynamic cache and will cause a pad error during generation.

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

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