1pp-0.5b-ua-tokmatch-sft

One Persona Pretraining (1PP) experiment model: 0.58B parameters, pretraining condition rewritten conversations, user+assistant loss, followed by supervised fine-tuning (SFT).

Token-matched branch of 1pp-0.5b-ua-sft: the production run continued from its step-12,000 checkpoint under a shorter schedule (same seed, optimizer state and batch order, 10% linear decay) that ends at step 17,396, where the run has trained on 33.745B supervised tokens, the total of the assistant-turn-loss condition over its full 31,777 steps. It answers whether the user+assistant condition's advantage is a supervised-token-count effect: at equal supervised tokens this branch saw 55% of the documents and compute of the assistant-only run. SFT as for the main models (matrix LR of the seed-28 sweep).

Part of a 3 × 3 study: three sizes (0.5B, 1B, 1.7B) × three pretraining conditions on the same 47.8M source documents in the same order (original documents; rewritten conversations with loss on assistant turns; rewritten conversations with loss on user and assistant turns). Every run saw the identical batch sequence, so the conditions differ only in the document text and the loss mask. Models are grouped in the 1pp collection.

Architecture

Llama-style decoder, 24 layers, hidden 1,152, FFN 4,608 (SwiGLU), attention heads / KV heads 9 / 3 (head dim 128), RMSNorm, RoPE base 10,000, untied embeddings, no biases, no QK-norm, sequence length 4,096. Tokenizer: SmolLM2 vocabulary (49,152) plus <|pad|>; <|endoftext|> is the end-of-document token.

Pretraining

Data: the 1PP conversations rewritten from those documents; loss on user and assistant turns (no loss on <|endoftext|>). One pass over 47.8M documents (66.2B tokens of original documents; 63.0B tokens as conversations), 31,777 steps at global batch 512 × 4,096 tokens, cross-document attention masking, best-fit packing with step-aligned document assignment. Optimizer: Muon (shape scaling, matrix LR 0.005) with Adam for embeddings and norms, warmup 2,000 steps, constant, linear decay over the last 10% to 1/100, weight decay 0.1, bf16.

Validation loss (per token, 2,433 held-out documents, final checkpoint):

Supervised fine-tuning

One epoch over a 400k-conversation mix: jkminder/model-raising-pb-100k-3c-mt-sft (98.5k multi-turn, constitution-cited track), dlab-spp/sp-sft-normal-300k minus prompts duplicated in the first set (271.6k), and a 30k sample of dlab-spp/sp-sft-safety-180k. Same stack as pretraining (Megatron, Muon, ChatML without a system turn, loss on assistant turns only). Matrix LR 0.002 selected per model from {0.0005, 0.001, 0.002, 0.005} by held-out loss (on the full-run model of this size and condition); global batch 128 × 4,096, linear decay to 1/10 after 3% warmup.

Held-out SFT loss (assistant tokens, 1,998 held-out conversations): 2.037

Chat format

ChatML without a system turn (the models never saw one):

<|im_start|>user\n{message}<|im_end|>\n<|im_start|>assistant\n{reply}<|im_end|>\n

The bundled chat_template renders exactly this. Generation stops at <|im_end|> (id 2) or <|endoftext|> (id 0); both are listed in eos_token_id.

Verification

The HF weights were checked against the Megatron checkpoint by recomputing validation losses with this model:

Links

• Training logs: wandb projects 1pp-training and 1pp-sft
• Research artifact from the 1PP project (EPFL DLAB); not a general-purpose assistant.