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LEAP reuses the serving model's own prefill hidden states to predict output length, cutting per-token latency 15.9 to 40.8 percent

AspireAI community · arXiv (cs.LG, cs.CL)
Length-aware scheduling reduces serving latency by running shorter requests first, but length predictors degrade under domain shift and need costly retraining, and their overhead can cancel the benefit. LEAP reuses the serving model's prefill hidden states, which already carry output-length information, and extracts the signal with a linear readout that adapts at test time through recursive least squares using completed requests as supervision, with no gradient computation or historical-data replay. Prediction and updates run asynchronously on CPU while prediction and initial batch ordering overlap the remaining GPU prefill. The authors report that online adaptation improves Spearman correlation by 64.7 percent under a larger domain shift, that serving experiments cut average per-token latency by 15.9-40.8 percent against the evaluated length predictors, and that it reaches 1.9 percent higher throughput with 30,569 times fewer predictor parameters than the strongest baseline. The comparisons are against the predictors the authors evaluated, not against every scheduler in production.
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