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Diffusion drafters were trained against the wrong targets, because a verifier sees tokens the drafter could not

AspireAI community · arXiv (cs.CL)
Speculative decoding cuts inference cost, and one-step diffusion drafters propose a block of several tokens in parallel to cut the sequential cost further. On-policy distillation trains them with verifier feedback on their own proposals, but parallel drafting makes that feedback mismatched: the drafter predicts each token without seeing the preceding tokens sampled in the same block, while the verifier conditions on those tokens, so different sampled prefixes imply different targets for the same prediction, and training on them separately can suppress tokens that are plausible under some prefixes. Multi-Draft On-Policy Distillation samples several draft blocks from the same context and aggregates the verifier's full-vocabulary conditionals across their prefixes, improving acceptance length beyond the pre-training level without changing the drafter's architecture or inference procedure.
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