1pp-1.7b-ua-sft
One Persona Pretraining (1PP) experiment model: 1.66B parameters, pretraining condition rewritten conversations, user+assistant loss, followed by supervised fine-tuning (SFT).
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 2,048, FFN 8,192 (SwiGLU), attention heads / KV heads 16 / 4 (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):
| assistant text | user text | document text |
|---|---|---|
| 1.431 | 1.338 | 3.119 |
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; global batch 128 × 4,096, linear decay to 1/10 after 3% warmup.
Held-out SFT loss (assistant tokens, 1,998 held-out conversations): 1.829
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|>.
Verification
The HF weights were checked against the Megatron checkpoint by recomputing validation losses with this model:
| set | HF loss | Megatron reference | abs. diff |
|---|---|---|---|
| sft_val segments [3, 4] | 1.8294 | 1.8294 | 0.0000 |
Links
- Training logs: wandb projects 1pp-training and 1pp-sft
- Research artifact from the 1PP project (EPFL DLAB); not a general-purpose assistant.