smollm2-360m-boolq-calibration-sft-v1

SFT warm-start checkpoint from slm-calibration-rlcd — a project training small LMs to make calibrated yes/no decisions, inspired by TypeSafe AI's "Jev" model / "RLCD" (Reinforcement Learning for Calibrated Decisions). Full project: 25b3nk/slm-calibration-rlcd.

This is not yet the final model — it's the SFT stage that teaches the tagged output format and baseline task competence, before GRPO (with a combined correctness + Brier-score reward, RLCR-style — arXiv:2507.16806) teaches actual calibration on top of it. GRPO has not been run against this checkpoint yet.

What it does

Given a BoolQ-style passage + yes/no question, outputs:

<answer>yes|no</answer><confidence>0.XX</confidence>

Training

• Base: HuggingFaceTB/SmolLM2-360M-Instruct
• Full fine-tune (not LoRA), fp32 weights + fp16 mixed-precision autocast
• 3000 examples from google/boolq train split (with random passage truncation on ~35% of examples to induce genuine uncertainty)
• 2 epochs, lr 2e-5, effective batch size 16 (batch 2 x grad-accum 8), gradient checkpointing
• Confidence targets in training data are a coarse heuristic (0.92 full-passage, 0.65 truncated), NOT ground-truth calibration — this stage teaches format and competence; calibration is GRPO's job, not yet applied to this checkpoint.

Eval (500-example BoolQ validation slice, seed 0)

Metric	Zero-shot baseline (same base model)	This checkpoint
Format compliance	n/a	1.0
Accuracy	0.626 (62% majority-class floor)	0.792
Brier score	0.344	0.182
ECE	0.335	0.130

Baseline used logit-extracted confidence (P(yes) vs P(no) at the answer position, since the untrained model has no reason to verbalize a number reliably); this checkpoint's confidence is read from its own generated <confidence> tag.

Even before GRPO, SFT alone closed a substantial part of both the accuracy and calibration gap versus zero-shot. ECE 0.130 is still far from well-calibrated (0 = perfect) — that's the gap the next stage (GRPO with combined correctness+Brier reward) targets.

Full design + ADRs

• ADR-0001: initial design + compute
• ADR-0002: SFT warm-start config + results