🥖 Baguettotron-600M

Baguettotron-600M is a 0.6B-parameter reasoning model trained from scratch on 158B tokens of SYNTH, a fully synthetic corpus amplified from 58,698 Wikipedia articles. It is the main reference model of our NeurIPS 2026 paper, It's All Training: A Fully Synthetic Single-Stage Recipe for LLMs.

• Single training stage: no separate mid-training, SFT or RLHF. The model follows instructions, reasons in <think> traces and recalls facts because SYNTH trains those capabilities directly.
• Token-efficient: within 4.7 points of Qwen3-0.6B on 22 multiple-choice tasks and 0.7 points on 8 open-ended tasks, trained on ~230× fewer tokens.
• Factually precise: highest FActScore in its parameter tier (41.7% macro vs. 31.6% for Qwen3-0.6B).

Model design

Baguettotron-600M is a standard dense decoder (Llama/Qwen-style) and loads natively in transformers and vLLM (LlamaForCausalLM, no remote code).

Training

• Data: SYNTH, 158.3B tokens (~2 passes over the ~75B-token corpus)
• Steps: 151,000 at global batch 512 × 2,048 tokens (~1.05M tokens/step)
• Optimizer: AdamW, peak LR 1.5e-3, 10k-step warmup, linear decay over the final 16.6% of steps to 0.2% of peak; weight decay 0.01, grad clip 1.0
• Hardware: 16× H100 (4 nodes × 4 GPUs) on MareNostrum 5 (BSC), torchtitan with FSDP, ~52.6 h, ~30% MFU

Evaluation

All scores are from the paper. Each model is prompted in its native format; Baguettotron models get no system prompt and have <think>\n seeded after the assistant turn.

• Ties or beats Qwen3-0.6B on TruthfulQA (42.6 vs. 32.7), ESGenius (62.2 vs. 55.1) and FormationEval (62.8 vs. 58.0)
• Weak: benchmarks that reward broad web knowledge (ARC-Challenge, GeoBench), since SYNTH covers only its seed articles
• Data, not architecture: the same architecture, tokenizer and step count trained on FineWiki or FinePDFs-Edu reaches only 26.1 / 25.1 on MCQ, even after SmolTalk post-training
• Reasoning traces matter: retraining without traces costs 9.1 points on TruthfulQA and 10.0 on NuclearQA

Prompt format

The model was trained on ChatML with a <think> block and no system prompt. The bundled chat template opens the assistant turn with <think>\n:

<|im_start|>user
What do you know about the Treaty of Westphalia?<|im_end|>
<|im_start|>assistant
<think>

The model writes its reasoning, closes it with </think>, answers, and ends the turn with <|im_end|>.

RAG. Pass sources inside the user turn. The answer then cites them with <ref>[quote]</ref>:

<|im_start|>user
{question}

<source_1>[…]</source_1>
<source_2>[…]</source_2><|im_end|>
<|im_start|>assistant
<think>

Reasoning notation. Traces use SYNTH's compact stenographic style (→ derivation, ↺ backtracking, ∴ conclusion, …). The confidence markers ● (high), ◐ (partial) and ○ (low) are informative: on traces dominated by uncertain markers, FActScore drops from 0.44 to 0.40, and the model commits to ~15–20% fewer facts. See the Baguettotron-350M card for the full notation.

Inference

vLLM

vllm serve PleIAs/baguettotron-600m --reasoning-parser deepseek_r1

--reasoning-parser deepseek_r1 moves the <think> trace into a separate reasoning field. Tested with vLLM 0.24.0.

from openai import OpenAI

client = OpenAI(base_url="http://localhost:8000/v1", api_key="EMPTY")
resp = client.chat.completions.create(
    model="PleIAs/baguettotron-600m",
    messages=[{"role": "user", "content": "What do you know about the Treaty of Westphalia?"}],
    temperature=0.1,
    top_p=0.95,
    presence_penalty=0.1,
    max_tokens=1536,
)
print(resp.choices[0].message.reasoning)  # <think> trace
print(resp.choices[0].message.content)    # answer

Recommended sampling: temperature=0.1, top_p=0.95, presence_penalty=0.1. Prompt and generation share the 2,048-token context, so keep max_tokens below 2,048 minus the prompt length.

Transformers

from transformers import AutoModelForCausalLM, AutoTokenizer

repo = "PleIAs/baguettotron-600m"
tokenizer = AutoTokenizer.from_pretrained(repo)
model = AutoModelForCausalLM.from_pretrained(repo, dtype="bfloat16", device_map="auto")

messages = [{"role": "user", "content": "What do you know about the Treaty of Westphalia?"}]
inputs = tokenizer.apply_chat_template(
    messages, add_generation_prompt=True, return_tensors="pt"
).to(model.device)
out = model.generate(inputs, max_new_tokens=1536, do_sample=True, temperature=0.1, top_p=0.95)
print(tokenizer.decode(out[0, inputs.shape[1]:]))

Limitations

• 2,048-token context shared by prompt, reasoning and answer
• Knowledge is bounded by the seed corpus (~58.7k Wikipedia articles): recall is precise on seed topics and weaker outside them
• Reasoning traces are English-only, even when the prompt and answer are in another language
• No preference tuning or safety alignment; not intended for high-stakes use without further evaluation

Citation

@inproceedings{langlais2026itsalltraining,
  title         = {It's All Training: A Fully Synthetic Single-Stage Recipe for {LLMs}},
  author        = {Langlais, Pierre-Carl and Delobelle, Pieter and Detrois, Yannick and Chizhov, Pavel and Rosas-Hinostroza, Carlos and Si Smail, Neil and Burtin, Benjamin and Shcharbakova, Hanna and Yamshchikov, Ivan and Stasenko, Anastasia},
  booktitle     = {Advances in Neural Information Processing Systems},
  year          = {2026},
  eprint        = {2609.37891},
  archivePrefix = {arXiv},
  primaryClass  = {cs.CL},
  url           = {https://arxiv.org/abs/2609.37891}
}

Acknowledgements

Trained on MareNostrum 5 (BSC) through the EuroHPC Extreme Scale Access call (EHPC-EXT-2025E01-092, JULIP: Powerful LLMs made in Europe). Parts of this research received funding from SPRIN-D, the German Federal Agency for Breakthrough Innovation.