DFlash2

This repository contains the promoted DFlash2 draft head used with Qwen/Qwen3.8-27B. It is not a fine-tune of the full Qwen target and must not be loaded as a standalone language model. It has no tokenizer and no target weights: a compatible DFlash2 runtime loads this head alongside the Qwen verifier.

The Hub base-model tree is intentionally omitted. A conventional "Qwen finetune" label would misrepresent the artifact: only the small speculative draft head is changed, while target-controlled output remains the authority.

The head descends from the public Qwen3.8-27B DFlash2 draft model. It was adapted with target-verified cycles from the incumbent legacy corpus and a session-grouped Fable agentic corpus. The final checkpoint combines a generation-2 Fable adaptation at strength 0.0625 with a generation-3 combined-domain adaptation at strength 0.1875.

No trace dataset, prompt file, capture cycle, selector tensor, or W&B log is included in this repository. Only the final draft checkpoint, configuration, blend metadata, and evaluation summary are published.

Acceptance results

All acceptance runs used greedy target-controlled generation on one Apple M4 Max through DFlash MLX. The target was the calibrated Qwen3.8-27B MXFP4 runtime. Draft quantization was disabled for this head.

Paired gate	Incumbent	This head	Mean delta	Wins / ties / losses
Legacy 24-prompt corpus	0.6712239583	0.6718750000	+0.0006510417	5 / 14 / 5
Fable 25-prompt held-out	0.6471875000	0.6492187500	+0.0020312500	11 / 5 / 9

The Fable live-gate prompts were excluded from the generation-2 and combined training splits. The legacy corpus had already been used to train the incumbent, so it remained in the combined training capture for a paired comparison.

Exact parity

The exact 256-token baseline-versus-DFlash smoke gate passed:

• token_match: true
• smoke acceptance: 0.7109375
• diagnostic baseline throughput: 21.9615 tok/s
• diagnostic DFlash throughput: 33.5111 tok/s

Throughput is diagnostic only. Thermal pressure and co-tenant machine load were not controlled.

Training summary

• combined capture: 11,273 target-verified cycles
• prompt groups: 127
• legacy contribution: 1,981 cycles from 24 prompts
• Fable contribution: 9,292 cycles from 103 training prompts
• excluded Fable live gate: 25 prompts
• teacher signal: target top-64 logits and greedy target tokens
• final full-run held-out prefix accuracy: 0.7932212528
• final full-run held-out top-1 accuracy: 0.8714877986

The capture teacher was the calibrated MXFP4 Qwen3.8-27B target runtime, not the pinned BF16 Qwen3.8-27B checkpoint. This precision choice is part of the training provenance.

Checkpoint integrity

• model.safetensors SHA-256: c90e0fc65dddbe4107b1b417d771c3be188c87197e89cf4b14415f56abc866f0
• config.json SHA-256: 873e3556509b0da06e29654ba00d4944888d4b5e8a33afde25f7eb27d321e980
• blend.json SHA-256: e53a6bb5e890d7e3368053302189766c3ef68d2eb7887152ece1ea9eac4f64d5

Intended use and limits

This artifact is for lossless speculative decoding research with a compatible DFlash2 implementation. Acceptance metrics do not establish broad task quality, natural-EOS behavior, multilingual performance, long-context performance, or a controlled thermal throughput win. The Fable held-out prompts come from the same eval shard as the Fable training prompts, so that gate does not prove out-of-domain generalization.