DEEP EXPLANATION

What Is Speculative Decoding? (ANSWERED)

Model BasedLLMsMedium12 min read

Model question on speculative decoding — draft model, target verification, lossless speedup, and production deployment notes.

TL;DR — Quick Answer

Speculative decoding uses a small draft model to propose several tokens quickly; the large target model verifies them in parallel in one forward pass. Accepted tokens advance faster than sequential decoding — lossless vs target-only sampling when verification matches exact decoding rules. Speedup depends on acceptance rate (draft quality and alignment). Used in inference servers (vLLM, TensorRT-LLM) for latency-sensitive serving — not a replacement for model routing or quantization.

The Interview Question

What is speculative decoding and how does it speed up LLM inference without changing outputs?

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