K2H main run, step 900

Step 900 of a planned 7,391-step continued-pretraining run on IFM/K2-Horizon-MoVA-36B-A4B. The run was stopped here because general skills were drifting down; the shorter clean-data arms (k2h-c1-clean, k2h-c2-sft, k2h-c4-ctrl) followed.

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.
  • 900 steps of a planned 7,391. Sequence length 32,768, about 786k tokens per step, about 0.71B tokens in total.
  • AdamW, beta1 0.9, beta2 0.95, weight decay 0.06, gradient clip 1.0.
  • Learning rate 1.5e-5, 100 warmup steps, warmup-stable-decay schedule (stopped in the stable phase).

Data mix (sampling weights):

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 84.6 -5.5
GSM8K, chat zero-shot (reasoning on) 96.6 not measured
IFEval, prompt-strict (reasoning on) 84.3 71.2 -13.1
MMLU 77.3 76.0 -1.3
ARC-Challenge 57.6 56.4 -1.2
ARC-Easy 85.6 85.3 -0.3
BoolQ 88.4 87.5 -0.9
HellaSwag (norm) 67.6 67.5 -0.1
PIQA 80.5 81.0 +0.5
WinoGrande 69.1 70.6 +1.5
MBPP pass@1 65.2 69.6 +4.4
HumanEval pass@1 (4 samples) 53.0 63.4 +10.4
Held-out PR NLL (lower is better) 1.519 1.173 -0.346

What the numbers say:

  • The held-out PR NLL drops from 1.519 to 1.173: the domain gain is large.
  • General skills drift down: GSM8K -5.5, IFEval -13.1, MMLU -1.3, ARC-Challenge -1.2. Coding goes up (MBPP +4.4, HumanEval +10.4).
  • Chat-format GSM8K was not measured for this checkpoint.
  • The full training state (with optimizer) is in Avifenesh/k2h-ckpt900-xllm.

License

Apache-2.0, the license of the base model.

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