Metis-1.5-think

Metis-1.5-think is the instruction-tuned variant of Metis-1.5-base — an 898M-parameter (≈340M active/token) single-latent Mixture-of-Experts model that was pretrained from scratch on 50B tokens and then supervised-fine-tuned to follow instructions, chat, and reason. Trained end to end in pure JAX on a single TPU v6e-8.

Unlike the base model (which only continues text), Metis-1.5-think answers: give it an instruction or a question and it responds directly. It answers concisely and does not emit a visible <think> chain-of-thought — its instruction data was trained without retained reasoning traces, so it states answers rather than narrating its reasoning.

[!NOTE] This is a small model (≈340M active params). It follows instructions and reasons at a level appropriate to its size — capable and surprisingly coherent for sub-1B, but not competitive with multi-billion-parameter assistants. It has no RLHF; alignment comes only from a safety subset in the SFT mix.

At a glance

Chat format

Metis-1.5-think was fine-tuned with a simple role-tagged template:

User: {your message}
Assistant: {model reply}

For a single turn, prompt the model with (a leading <bos> token, then):

User: <your message>
Assistant: 

and let it generate until <eos>. Multi-turn conversations stack User:/Assistant: lines in order. A system message may be prepended as System: {content}\n. The model answers directly — it does not emit <think> reasoning blocks.

Training data (SFT mix)

~1.15M examples (fixed 1024-token windows, prompt tokens loss-masked), assembled from open instruction & reasoning datasets, then English-filtered, deduplicated, and decontaminated against the standard benchmark suite (MMLU, GSM8K, MATH, ARC, HellaSwag, …). Roughly:

Chat & instruction (~0.75M) — Tülu-3 (general instruction, writing/summarization, safety), WildChat (cleaned real prompts), SmolTalk (everyday, system-chats, rewrite, summarize, magpie, system-constraints), OpenHermes, SciRIFF (science instruction & reference tasks), OpenStax reference QA, and a small identity set.

Reasoning & math (~0.38M) — OpenR1-Math (verified), NuminaMath (CoT medium/olympiad, 1.5 verified), OpenThoughts-3 (math, science, general non-code), Bespoke-Stratos (proofs), s1K (symbolic proofs), TemplateGSM, and reasoning-style SmolTalk. These were used as direct-answer supervision — the source <think> reasoning traces were stripped during data prep — so the model learns to answer math/reasoning prompts rather than to narrate a visible chain-of-thought. (A future revision could retain the traces to make it an explicit chain-of-thought model.)

Safety — a Tülu-3 safety subset (~60k) for basic refusal/safety behavior.

Credit for the underlying datasets belongs to their original authors (see Acknowledgements).

Training procedure

• SFT from Metis-1.5-base (initialized from base params; fresh optimizer/schedule).
• ~1.2 epochs, ≈2,685 steps, global batch 64 × 8 grad-accum (≈524k tokens/step), sequence length 1024.
• Optimizer: AdaMuon (Newton–Schulz-orthogonalized momentum + Adam), fp32 master weights / bf16 compute, base LR 4e-5 with short warmup + cosine decay.
• Prompt tokens are loss-masked (-100); the model only learns to produce the assistant turns.
• Pure JAX/XLA on one TPU v6e-8, ≈245k tokens/sec. SFT cross-entropy fell from ≈1.70 to ≈1.11 over the run.
• Identity-alignment patch: a short follow-up SFT pass (identity Q&A + general-data rehearsal) so the model identifies as Metis, created by Lernex — rather than inheriting the identity of the assistants its instruction data was partly distilled from.

Evaluation

0-shot accuracy on the full test split of each benchmark, scored with a custom JAX harness — multiple-choice by length-normalized loglikelihood (acc_norm) or plain loglikelihood (acc); GSM8K by greedy generation (chat template + flexible numeric extraction). Training data was decontaminated against these benchmarks, so these are clean held-out numbers.

¹ BoolQ majority-class baseline ≈ 62%. GSM8K not run for the base model (non-instruct).

How to read these. Metis-1.5 is a ~340M-active model (898M total, MoE) trained on only 50B tokens — far fewer than the 0.3–18T behind modern sub-2B models — so it lands around GPT-2-medium tier: clearly above chance on ARC-Easy, modestly so on HellaSwag / PIQA / WinoGrande, and at chance on MMLU. Supervised fine-tuning leaves raw knowledge roughly unchanged (base ≈ think on multiple choice) while adding instruction-following — visible on BoolQ (+9.5) and GSM8K (7.6%), the latter notably strong for the scale (TinyLlama-1.1B / Pythia-1B sit ~2–3%), reflecting the math/reasoning-heavy data mix. The clearest lever for higher scores is more training tokens, not a different architecture.

Intended uses & limitations

Use it for — instruction following, lightweight chat, and math/reasoning demonstrations at small scale; research on efficient MoE post-training; a base for further fine-tuning or preference optimization.

Limitations

• Small model — limited world knowledge and reasoning depth; will confidently hallucinate.
• No RLHF / preference optimization — only SFT, with a modest safety subset; not a safety-aligned assistant.
• English-only, 1024-token context.
• Answers on reasoning/math prompts are frequently wrong even when fluent, and the model does not show its work (no chain-of-thought) — verify anything important.

How to use

[!NOTE] Weights use JAX-native tensor names and a custom architecture, so this does not load via transformers.AutoModel. It ships as a self-describing safetensors release (config.json has all dims; the base model card documents the forward pass).

Load the raw tensors with safetensors and run the forward described in the base model card, wrapping inputs in the chat template above:

from safetensors import safe_open
weights = {}
with safe_open("model.safetensors", framework="numpy") as f:
    for k in f.keys():
        weights[k] = f.get_tensor(k)

# Prompt format (prepend <bos>, id 1):
#   "User: <message>\nAssistant: "
# Generate to <eos> (id 2); stop early if "\nUser:" appears.

A reference JAX/CPU chat implementation (KV-cache decode + this template) is part of the Metis training stack; a standalone single-file loader is a planned follow-up.

License

Released under CC0-1.0 — public-domain dedication. Use, modify, redistribute, fine-tune, or build on Metis-1.5-think for any purpose, with no restrictions and no attribution required. Provided as-is, without warranty. (Underlying SFT datasets retain their own licenses; CC0 applies to these released weights.)

Citation

@misc{metis15think2026,
  title  = {Metis-1.5-think: An instruction-tuned single-latent MoE language model},
  author = {Lernex},
  year   = {2026},
  howpublished = {Hugging Face},
  note   = {898M params (340M active); SFT of Metis-1.5-base on ~1.15M curated examples, JAX/TPU v6e-8}
}

Acknowledgements

Thanks to the open instruction/reasoning-data community — Tülu-3 (AI2), WildChat, SmolTalk, OpenHermes, SciRIFF, OpenStax, OpenR1, NuminaMath, OpenThoughts, Bespoke-Stratos, s1K, and TemplateGSM — and to the JAX and Cloud TPU teams.