| # Phase 2.1A step budget v2 |
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| Date: 2026-08-27 |
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| ## Decision |
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| 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. |
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| ## Scale calculation |
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| - 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. |
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| 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. |
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| ## Evidence from the stopped v1 run |
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|
| 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. |
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| ## Selection protocol |
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| - 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. |
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| 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. |
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| ## Restart boundary |
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| 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. |
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