JetSpec++: Foresight Parallel Drafting with Self Refinements

Speculative decoding's effectiveness is governed by two quantities: the acceptance rate of drafted tokens and the cost of producing them. We show the two objectives can be co-optimized with algorithm-system co-design, and present JetSpec++, which retains a strong learned draft model while hiding its cost almost entirely. JetSpec++ combines three components: intra-block self refinement, which trains the draft model to iteratively correct its own parallel predictions within a block of tokens; inter-block foresight drafting, which begins the next block before the current one is verified; and pipelined drafting and verification, which overlaps the two stages so drafting's marginal wall-clock cost approaches zero. In comparison with state-of-the-art speculative decoding methods, JetSpec++ attains a wall-clock speedup of up to 6.74× over autoregressive (AR) decoding and 1.41× over DSpark, with up to 1250 TPS single-request throughput on GB200, and an average acceptance length of 7.60 across seven benchmarks, while preserving the target model's output distribution.