MTP HEAD ONLY — NOT A STANDALONE LANGUAGE MODEL. This repository contains a replacement BF16 MTP draft head, model-mtp.safetensors (844.6M parameters, 19 fused tensors, 1.689 GB). It does not contain the Ornith target weights. For ready-to-serve merged checkpoints, use shisa-ai/Ornith-1.5-35B-A3B-MTP for the full BF16 target or shisa-ai/Ornith-1.5-35B-A3B-MTP-FP8 for the official FP8 target with this same BF16 MTP head.

Component	Size	Notes
BF16 MTP head	844,640,768 params / 1.689 GB	19 exported `mtp.*` tensors

The head is initialized from the compatible MoE MTP head in Qwen/Qwen3.6-35B-A3B, then re-aligned to Ornith-1.5's hidden states with full-vocabulary KL distillation. The final 12K run is a two-epoch, code-heavy warm-start from our earlier 5K KL-distilled head.

Why replace the shipped Ornith-1.5 MTP head?

The official Ornith-1.5 checkpoint includes a native 785-tensor MTP head, but it performed poorly in our matched vLLM tests. On ShareGPT-style MTP3 rows it accepted only 21.7% of proposed draft tokens and reached 0.71x/0.68x the AR throughput at concurrency 1/4.

This is consistent with the community report “mtp.* tensors look like random init, not trained weights”. Our own sample of the released BF16 tensors also found initializer-like statistics: q_proj std 0.01993 with kurtosis 2.997; expert-0 projections std 0.01996–0.01998 with kurtosis approximately 3; and mtp.norm.weight centered at 0.02281 rather than near 1. These observations do not prove provenance, but the weight statistics and serving behavior point in the same direction.

The low acceptance is not explained by target quantization:

Native shipped head	Base/config	MTP3 accept	Accepted length	Per-position accept P1/P2/P3
Native BF16	reduced 32K / 8-seq diagnostic	21.5%	1.65	56.4 / 7.3 / 0.9%
Native official FP8	full 262K config	21.7%	1.65	56.6 / 7.6 / 0.9%

The acceptance profile is effectively identical, so the native-head weakness is intrinsic to the head rather than an FP8 artifact.

Acceptance accuracy: native vs graft vs KL distillation

"Accuracy" below means speculative draft acceptance, not downstream task accuracy. vLLM's target verifier is still responsible for model correctness. The canonical gate used MTP3, temperature 0, concurrency 1, 10 prompts × 3 repetitions, and up to 384 generated tokens. The suite contains code, English-general, Japanese-general, and mixed Japanese/English prompts; the code subset has 12 requests.

MTP head	Training	Code accept	Code accepted length	Code P1/P2/P3	Overall suite accept
Ornith-1.5 native	none; shipped head	37.20%	2.116	85.2 / 22.9 / 3.5%	32.19%
Qwen3.6 direct graft	zero training	50.19%	2.506	80.8 / 44.7 / 25.1%	48.34%
5K KL distill	1 epoch, private-code corpus	66.99%	3.010	89.2 / 67.3 / 44.5%	58.62%
This 12K KL distill	2 mixed-data epochs, warm-started	69.27%	3.078	92.2 / 71.1 / 44.5%	60.51%

The final head is strongest on code. Relative to the zero-training graft, code acceptance improves by 19.08 percentage points and overall suite acceptance by 12.17 points. The 12K run adds another 2.28 points of code acceptance over the 5K distill, mostly at the first two speculative positions.

Performance context on the same code gate: AR produced 220.47 client output tok/s at 1737.80 ms p50 E2E; the direct graft produced 247.10 tok/s at 1531.69 ms; this head produced 273.09 tok/s at 1299.62 ms. These are local single-GPU measurements, not universal throughput claims.

The code-heavy tradeoff is visible on matched ShareGPT rows: the 12K head's acceptance was 47.19% at c=1 and 48.08% at c=4, essentially flat versus the 5K head (48.71%/47.79%), while output throughput was 2.0%/1.1% lower. This head is therefore a code-priority variant, not an across-the-board replacement.

Training scale

The final checkpoint accumulates two stages: an initial 5K code distill from the Qwen3.6 graft, followed by the broader 12K mixed-data warm-start.

Variant	Prompt pool	Train rows usable at 2K	Epochs	Optimizer updates	Initialization
Native head	—	—	—	0	Ornith release
Qwen3.6 graft	—	—	—	0	Verbatim Qwen3.6 MTP tensors
5K KL distill	5,000	1,850	1	462	Qwen3.6 graft
Final 12K KL distill	12,000 designed	10,460 used/epoch	2	5,230	5K KL head

For the final stage, 11,964 teacher trajectories were generated from 12,000 prompts (36 duplicate prompt keys); 11,963 parsed into a length-stratified split of 10,763 train and 1,200 validation rows. Of the training split, 10,463 rows had completion room under the 2,048-token training cap, and 10,460 were used so the batch packed evenly.

Data mix

The designed 12K prompt mix is 50% code, plus agentic, multilingual general, and translation coverage:

Category	Prompts	Share	Description
Private repository-derived code engineering	3,600	30.0%	Local code/repository and rollout-derived engineering patterns
Synthetic coding tasks	2,400	20.0%	Python, TypeScript, JavaScript, Bash, Rust, Go, C++, and HIP
Agentic/planning/tool scenarios	1,600	13.3%	Debugging, research, incident response, orchestration, review
English general	1,200	10.0%	Explanation, writing, practical Q&A
Japanese general	1,200	10.0%	Explanation, writing, practical Q&A
Korean general	500	4.2%	General prompts
Chinese general	500	4.2%	General prompts
Other-language coverage	500	4.2%	Traditional Chinese and mixed CJK/non-CJK coverage
Translation	500	4.2%	en↔ja, ko/zh→en, en→ko/zh, ja→ko, en→European-language prompts

The 2,400 synthetic coding prompts include 500 Python, 400 HIP, 300 Bash, 300 Go, 300 C++, 250 TypeScript, 250 Rust, and 100 JavaScript tasks. Translation includes 150 en→ja, 150 ja→en, 50 ko→en, 40 zh→en, 40 ja→ko, and smaller en→ko/zh/European-language buckets.

The private prompt and trajectory corpus is not included in this repository. It contains local code/repository-derived material. The table documents the mix, but it is not a claim that the training data is public, clean-room, or fully redistributable.

Corpus generation and KL process

Generate target trajectories. We sampled the official Ornith-1.5 FP8 target offline with reasoning enabled, temperature 0.7, top-p 0.95, and up to 2,048 output tokens. The 11,964 trajectories contain about 22.45M generated tokens (about 1,914 per row on average).
Length-stratified split. We split 10,763/1,200 train/validation across ten total-token buckets, then selected completion positions that fit the 2,048 training window.
Freeze the target. The BF16 ornith-ai/Ornith-1.5-35B-A3B target and shared LM head are frozen. Only the 844.6M MTP-head parameters are optimized.
Match the full target distribution. At completion positions, the MTP head consumes Ornith's post-norm hidden state plus the next-token embedding. Its hidden output and the target hidden state are projected through the same frozen LM head, and we minimize full-vocabulary KL divergence at T=1.0. This follows the key result from protoLabsAI/Ornith-1.0-9B-MTP: hard CE on sampled tokens can sharpen the wrong distribution, while speculative acceptance rewards matching the target distribution.
Warm-start and export. We warm-start from the 5K KL head, train two epochs at LR 5e-5 with a 5% warmup and cosine decay, then export 19 BF16 fused mtp.* tensors for vLLM. The official FP8 target weights remain unchanged.

Training efficiency: 4.25× faster

We adapted the original protoLabs technique first for shisa-ai/Ornith-1.0-35B-FP8-BLOCK-MTP, then optimized the 1.5/35B MoE training path:

pack four 2,048-token rows per forward while preserving the same 8,192-token optimizer batch;
project only completion positions into the 248K vocabulary;
use an FLA/Triton fused full-vocabulary KL that computes gradients only for student hidden states, skipping the frozen 1 GB LM-head gradient;
use BF16 for LM-head projection and FP32 for softmax/KL reduction;
enable high matmul precision/TF32 and fused AdamW.

On one RTX PRO 6000 Blackwell 96 GB GPU, our own measured update time fell from 12.0 to 2.82 seconds/update (4.25×) at 84.24 GiB peak allocation. The full 5,230-update run finished in about four hours instead of the naive ~17.4-hour projection. This is a before/after comparison of our implementation, not a cross-hardware benchmark against protoLabs.

Why this upload keeps the BF16 head

We also tested MTP-head-only FP8_BLOCK post-training quantization with the same Triton draft-MoE backend:

Head/backend	Head payload	Model load	Logical KV tokens	Code accept	Code tok/s	ShareGPT c1/c4 tok/s
BF16 / Triton	1.689 GB	36.04 GiB	4.115M	65.26%	277.32	221.68 / 547.18
FP8_BLOCK / Triton	0.854 GB	35.26 GiB	4.247M	66.47%	261.81	220.89 / 495.04

FP8 saved 0.78 GiB of loaded model memory and added 3.2% logical KV capacity, but regressed code throughput by 5.6% and ShareGPT c4 by 9.5% against the backend-matched BF16 control. Acceptance did not collapse, so the current cost appears to be the draft FP8 kernel path rather than head quality. This upload therefore keeps the MTP head in BF16.

Using the head

This repository is a sidecar. Do not point vLLM or Transformers directly at this head-only repository. The native Ornith-1.5 MTP tensors must be removed from the target index/shard and replaced by these 19 fused tensors; merely copying this file over the official checkpoint is not a safe merge procedure.

Ready-to-serve merged releases are available with either the full BF16 Ornith target or the official FP8 Ornith target. The replacement-aware graft/distillation workflow is based on the recipe published with protoLabsAI/Ornith-1.0-9B-MTP.

The locally tested vLLM 0.27.1 command shape below uses the FP8 merged release:

bash

MODEL=shisa-ai/Ornith-1.5-35B-A3B-MTP-FP8

vllm serve "$MODEL" \
  --served-model-name ornith-1.5-35b-mtp \
  --trust-remote-code \
  --quantization compressed-tensors \
  --language-model-only \
  --max-model-len 262144 \
  --gpu-memory-utilization 0.93 \
  --max-num-seqs 32 \
  --max-num-batched-tokens 32768 \
  --max-cudagraph-capture-size 32 \
  --attention-backend flashinfer \
  --kv-cache-dtype fp8 \
  --calculate-kv-scales \
  --generation-config vllm \
  --no-enable-prefix-caching \
  --speculative-config '{"method":"mtp","num_speculative_tokens":3}'

Use gpu-memory-utilization=0.93 as the starting point on a 96 GB GPU. At 0.95, all tested MTP depths hit reproducible temporary GDN/FLA workspace OOMs on the first 32K-prefill row. The 0.93 matched recovery passed 80/80 rows. Re-benchmark memory utilization, depth, and concurrency on your own hardware.

Limitations and correctness status

Experimental; not promoted as a production default. On vLLM 0.27.1, selected long-output and c16 greedy rows differed reproducibly between AR and speculative modes. One unchanged diagnostic prefix showed a material target decision shift, not just an exact tie. We also observed deterministic output sensitivity to max_tokens and to OpenAI logprob instrumentation.
Exact AR/spec divergence was established only for vLLM. Our SGLang DFlash rows did not include a matched same-engine SGLang AR token-capture baseline, so cross-engine hash differences must not be presented as proof of the same SGLang correctness failure.
Speculative decoding is intended to preserve the target distribution, so these differences are a runtime correctness investigation—not an accuracy/speed tradeoff that this model card silently accepts.
Automatic prefix caching was disabled because the tested hybrid GDN + MTP path has known local correctness issues.
The head was trained with a 2,048-token window. Long-context acceptance was measured, but the training distribution does not directly cover 256K input.
The data mix is code-heavy and private/synthetic. ShareGPT acceptance did not improve over the 5K head.
Evaluation was text-only (--language-model-only). Multimodal MTP behavior was not tested.
Acceptance benchmarks are small local diagnostics, not downstream Ornith task benchmark scores. For base-model capabilities and risks, see the official Ornith-1.5 model card.

DFlash context-length cross-check

The community discussion also suggests DFlash as an alternative and notes that its acceptance falls at longer context. We reproduced the general long-context decline in both engines, with a clear DFlash decline by 64K:

Prompt length, 8K output	vLLM DFlash N16 accept	SGLang DFlash B16 accept
8K	89.8%	90.0%
32K	89.3%	90.4%
64K	77.5%	78.6%
128K	63.5%	66.9%
~252K	48.8%	52.7%

Our retained output-length sweeps suggest DFlash declines more than MTP, with half-context being the apparent cross-over point where MTP outperforms DFlash:

Prompt	Output range	MTP3	DFlash N16
8K	512→32K	60.62→61.11%	91.48→88.61%
64K	8K→32K	58.95→58.97%	77.54→74.08%
131K	2K→32K	63.05→61.79%	65.84→61.83%

This speed degradation is separate from output correctness: low draft acceptance should normally make speculation slower, not change the target result.

Provenance, prior work, and license

Target model: ornith-ai/Ornith-1.5-35B-A3B
FP8 target: ornith-ai/Ornith-1.5-35B-A3B-FP8
MTP initialization donor: Qwen/Qwen3.6-35B-A3B
Original graft/KL-distillation technique and recipe: protoLabsAI/Ornith-1.0-9B-MTP
Our prior 35B adaptation: shisa-ai/Ornith-1.0-35B-FP8-BLOCK-MTP
Native-head investigation: Ornith discussion #10

This MTP head is a modified derivative of the Apache-2.0-licensed Qwen/Qwen3.6-35B-A3B MTP head: the Qwen donor weights were used as initialization and then changed by KL distillation against the MIT-licensed Ornith-1.5 target. Accordingly, this head repository is distributed under the Apache License 2.0; see the local LICENSE, NOTICE, and Qwen's upstream license.

shisa-ai/Ornith-1.5-35B-A3B-MTP-ONLY

Ornith-1.5-35B-A3B-MTP-ONLY