# Phase 2.1A step budget v2

Date: 2026-08-27

## Decision

Replace the inherited 15,000-step fixed run with a 3,000-step hard cap and
pre-registered ID-dev early stopping. Apply the same cap and selection rule to
Robometer-Low-LoRA and the future full-decoder Robometer-Low comparison.

## Scale calculation

- Frozen train set: 2,021 preference pairs.
- Effective batch: 64 pairs per optimizer step.
- 15,000 steps: 960,000 pair presentations, approximately 475 nominal passes.
- 3,000-step cap: 192,000 pair presentations, approximately 95 nominal passes.
- Minimum 1,000 steps: 64,000 pair presentations, approximately 32 nominal passes.

The official 15,000-step value was copied from the million-scale RBM-1M recipe;
it was not estimated from this 2,021-pair Low split.

## Evidence from the stopped v1 run

The user-stopped seed-7 run logged through step 246. Mean total train loss fell
from 4.573 over steps 1-25 to 3.218 over steps 201-225; the last-100-step linear
trend was still negative by about 0.455 per 100 steps. It had not converged.
However, the 15,000-step scheduler used 750 warmup steps, so step 246 had reached
only about 33% of the target learning rate. This curve cannot be extrapolated to
justify 15,000 steps.

## Selection protocol

- Scheduler: cosine with 5% warmup; 150 warmup steps at the cap.
- Evaluate every 250 steps on the original 108-pair `dev` split.
- Evaluate both A/B orientations for each pair.
- Select by the sum of mean preference, progress, and success ID-dev losses.
- Minimum training: 1,000 steps.
- Early stop after four consecutive evaluations without an improvement of at
  least 0.005 ID-dev loss.
- Restore the best ID-dev checkpoint for export.
- Do not use `confirmation_dev` or RBM-EVAL-OOD for selection.

The cap is a safety bound, not a claim that every seed needs exactly 3,000
steps. The selected step is an experimental result recorded per seed.

## Restart boundary

The v1 run is not resumed into v2. Its latest complete checkpoint is step 4,
and v2 changes both the scheduler horizon and checkpoint-selection protocol.
All v2 seeds must start from the same pinned base model in a new output root.