K2H c1-clean

Arm 1 of a continued-pretraining study on IFM/K2-Horizon-MoVA-36B-A4B: clean domain data plus unverified synthetic replay.

Research checkpoint, published 2026-11-03. It is not a release candidate. Compare it with the release, not in isolation.

Model

  • Base: IFM/K2-Horizon-MoVA-36B-A4B (36B total, about 4B active, MoE). Same architecture, tokenizer and chat template.
  • Weights: bf16 safetensors. The custom modeling code ships with the weights, so load with trust_remote_code=True.
  • Sampling as the base model card recommends: temperature 1.0, top_p 0.95.

Training

  • Trainer: xLLM, FSDP2, bf16, 3 GPUs.
  • Start: the released weights of IFM/K2-Horizon-MoVA-36B-A4B.
  • 100 steps. Sequence length 65,536, batch 1 per GPU, gradient accumulation 4: about 786k tokens per step, about 79M tokens in total.
  • AdamW, beta1 0.9, beta2 0.95, weight decay 0.06, gradient clip 1.0.
  • Learning rate 1.5e-5, 20 warmup steps, then constant.
  • Chat records, where present, are trained on assistant tokens only.

Data mix (sampling weights):

  • 44.5%: domain slices from Avifenesh/k2h-corpus-domain-clean (inference, framework, general and Linux code bundles, commits) plus pull-request text and a small slice of tuning notes that are not published.
  • 55.5%: synthetic replay from IFM/Math-Reasoning, IFM/Code-Reasoning and IFM/SFT-Reasoning after quality rules but before script verification (not published; the verified part is in Avifenesh/k2h-replay-verified).

Evaluation

All numbers come from the same harness as the release column (lm-evaluation-harness against a vLLM server). IFEval and chat GSM8K use the chat template with reasoning on, temperature 1.0, top_p 0.95, 14,336 new tokens, and score only the text after the reasoning block. The PR NLL is the mean token NLL on 150 held-out pull requests (530k tokens).

Task Release This model Change
GSM8K, 5-shot, strict 90.1 88.4 -1.7
GSM8K, chat zero-shot (reasoning on) 96.6 95.8 -0.8
IFEval, prompt-strict (reasoning on) 84.3 73.2 -11.1
MMLU 77.3 76.5 -0.8
ARC-Challenge 57.6 57.3 -0.3
ARC-Easy 85.6 85.2 -0.4
BoolQ 88.4 88.3 -0.1
HellaSwag (norm) 67.6 67.4 -0.2
PIQA 80.5 80.5 +0.0
WinoGrande 69.1 69.6 +0.5
MBPP pass@1 65.2 71.6 +6.4
HumanEval pass@1 (4 samples) 53.0 65.9 +12.9
Held-out PR NLL (lower is better) 1.519 1.332 -0.187

What the numbers say:

  • Coding goes up (MBPP +6.4, HumanEval +12.9) and most general tasks stay level.
  • Few-shot GSM8K drops 1.7 points (p=0.02, paired). Chat-format GSM8K is level (95.8 vs 96.6), so the few-shot gap is mostly format.
  • IFEval drops 11.1 points (p=2e-8). The model often writes "think..." after closing its reasoning block. The unverified replay is the likely cause: the control arm with verified replay (k2h-c4-ctrl) keeps IFEval level.

License

Apache-2.0, the license of the base model.

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