Kimi-K3.1-Dflash2-Preview

Overview

A DFlash2 speculator for Kimi-K3.1-Pro, designed to accelerate inference through speculative decoding with SGLang. In each step the draft proposes a block of tokens in parallel from the target's hidden states, and the target verifies the block in one forward pass.

This repository contains the BF16 draft weights and configuration. The target model supplies the embeddings, LM head, tokenizer, and native chat template. The draft is used alongside the target and is not a standalone language model.

The draft is a five-layer MLA stack. It reads hidden states from six target layers, fuses them through one projection, and runs block-causal sliding-window attention over the target's context. A low-rank candidate selector then picks each proposed token from the draft's top-k candidates, conditioned on the token before it, so the block is sampled as a path rather than position by position.

Model Specifications

• Base model: moonshotai/Kimi-K3.1-Pro
• Format: Single-file BF16 Safetensors, 2,784,811,008 parameters
• Draft: 5 MLA layers (DeepSeek-style multi-head latent attention), hidden size 7168, 96 heads, q LoRA rank 1536, KV LoRA rank 512, QK head dim 192 (128 + 64 RoPE), V head dim 128, SwiGLU MLP 14336
• Block convolutions: a learned convolution over the block (kernel 2, group size 16) in the attention and MLP branches of every layer
• Attention: Block-causal sliding-window attention with a 1,024-token window
• Verification width: 5 tokens (1 current token + 4 draft tokens) as configured; the same weights also serve at 8 (see below)
• Selector: Rank 256, top-k 32
• Auxiliary target layers: [7, 23, 51, 67, 83, 91]
• Configured context length: 1,048,576 tokens (YaRN, factor 32), aligned with the target
• Target weights: Embedding and unembedding weights are loaded from the target

The configured context limit is distinct from the attention window. The config alignment does not establish draft acceptance quality across the full 1M context.

Evaluation Results

acc_len is the per-request acceptance length L = C / V, where C is the number of completion tokens and V is the number of verification steps, averaged equally across successful requests. Completion-token-weighted AL is sum(C * L) / sum(C); pooled AL is sum(C) / sum(V). Every verification step commits the accepted draft tokens plus one token from the target, so AL is at most the verification width.

Verification width 5 (1 current token + 4 draft tokens, as configured)

Verification width 8 (1 current token + 7 draft tokens)

Measured with real DFlash2 and block verification enabled, thinking_effort max, temperature=1.0 and top_p=0.95, on one 8x B300 node (TP8) with FP8 target KV cache, FP8 draft KV cache and cutedsl_mla draft attention, using the command below. The three suites ran concurrently against one server, with 32 client workers per suite and at most 64 running requests at 5 tokens (32 at 8 tokens). These results are not from a single-request-at-a-time evaluation.

All 3,514 requests (1,757 per width) finished with an end-of-turn token. None was truncated (the longest used 104,938 of the 131,072-token context), and none needed a retry. Mean completion length at width 5: GSM8K 344, AIME26 9,806 and GPQA Diamond 5,761 tokens.

Prompts: each sample is one user turn rendered with the target's chat template. GSM8K and AIME26 append "Please reason step by step, and put your final answer within \boxed{}."; GPQA Diamond uses the simple-evals multiple-choice template with options shuffled per question. AIME26 is the 30 AIME 2026 problems from MathArena/aime_2026, sampled 8 times each with different seeds. Only acceptance length is measured here, not answer accuracy.

Serving with SGLang

The following example launches one TP8 replica with block verification, FP8 KV caches for the target and the draft, and cutedsl_mla draft attention:

python -m sglang.launch_server \
  --model-path moonshotai/Kimi-K3.1-Pro \
  --trust-remote-code \
  --tp-size 8 \
  --mem-fraction-static 0.85 \
  --mamba-full-memory-ratio 1.0 \
  --reasoning-parser kimi_k3 \
  --tool-call-parser kimi_k3 \
  --kv-cache-dtype fp8_e4m3 \
  --disable-radix-cache \
  --max-running-requests 64 \
  --context-length 131072 \
  --speculative-algorithm DFLASH \
  --speculative-draft-model-path RadixArk/Kimi-K3.1-Dflash2-Preview \
  --speculative-draft-attention-backend cutedsl_mla \
  --speculative-draft-kv-cache-dtype fp8_e4m3 \
  --speculative-num-draft-tokens 5 \
  --speculative-use-block-verification \
  --host 127.0.0.1 \
  --port 30000

For an 8-token verification width, pass --speculative-num-draft-tokens 8. It overrides the config's block_size of 5, and SGLang logs a warning. Also lower --max-running-requests to 32: the target's speculative Mamba state cache grows with verification width × running requests, and at 8 × 64 it leaves no memory for the KV cache at --mem-fraction-static 0.85 on B300.