Python4 AFT adapters (arcadia-impact/python4-gemma3-27b-aft)

Five matched rank-64 LoRA adapters for studying whether supervised Python4 code demonstrations activate held-out Python4 rules installed during midtraining. Python4 is a controlled fictional language, not a real Python release.

Experiment run: 20260811T052635Z. Each adapter saw the same ordered 512-row dataset for eight epochs (128 optimizer steps). The four held-out rule families never appear in AFT targets.

Primary generic-Python results

Parent / adapter	Python4 adoption pre → post	Boa pass pre → post	Held-in pre → post	Held-out pre → post	Held-out Δ (95% CI)
control	0.0% → 88.3%	0.0% → 26.6%	0.0% → 25.3%	0.0% → 2.4%	2.4% [0.0%, 6.1%]
mixed_1ep	0.0% → 89.8%	0.0% → 26.6%	0.0% → 25.1%	0.0% → 1.8%	1.8% [0.0%, 4.9%]
ordered_1ep	0.0% → 89.1%	0.0% → 22.7%	0.0% → 22.1%	0.0% → 3.0%	3.0% [0.5%, 6.3%]
mixed_4ep	0.0% → 89.1%	0.0% → 23.4%	0.0% → 22.1%	0.0% → 3.0%	3.0% [0.5%, 6.4%]
ordered_4ep	0.0% → 93.8%	0.0% → 26.6%	0.0% → 25.9%	0.0% → 0.6%	0.6% [0.0%, 2.0%]

Explicit-Python3 spillover and selectivity

Arm	Python3 pass pre → post	Python4 spillover pre → post	Selectivity Δ (95% CI)
control	56.2% → 0.0%	0.0% → 89.8%	-1.6% [-5.5%, 2.3%]
mixed_1ep	53.9% → 0.0%	0.0% → 90.6%	-1.6% [-7.0%, 3.9%]
ordered_1ep	54.7% → 0.0%	0.0% → 93.0%	1.6% [-2.3%, 5.5%]
mixed_4ep	53.1% → 0.0%	0.0% → 89.1%	4.7% [1.6%, 8.6%]
ordered_4ep	52.3% → 0.0%	0.0% → 93.8%	0.8% [-1.6%, 3.9%]

Adapter paths

• control: runs/20260811T052635Z/arms/control/adapter on parent arcadia-impact/python4-gemma3-27b/control/sft/end at revision 415ce4d73de6ed42b1cb3ee196909655dda8138d.
• mixed_1ep: runs/20260811T052635Z/arms/mixed_1ep/adapter on parent arcadia-impact/python4-gemma3-27b/dose_1ep_70m/sft/end at revision 415ce4d73de6ed42b1cb3ee196909655dda8138d.
• ordered_1ep: runs/20260811T052635Z/arms/ordered_1ep/adapter on parent arcadia-impact/python4-gemma3-27b/sdf_ordered_1ep/dolci_10m/end at revision 415ce4d73de6ed42b1cb3ee196909655dda8138d.
• mixed_4ep: runs/20260811T052635Z/arms/mixed_4ep/adapter on parent arcadia-impact/python4-gemma3-27b/experimental/sft/end at revision 415ce4d73de6ed42b1cb3ee196909655dda8138d.
• ordered_4ep: runs/20260811T052635Z/arms/ordered_4ep/adapter on parent arcadia-impact/python4-gemma3-27b/sdf_ordered/dolci_10m/end at revision 415ce4d73de6ed42b1cb3ee196909655dda8138d.

The dataset and executable benchmark are in arcadia-impact/python4-leetcode-aft at revision 06ef77ffc8ef805b6110eb5dacd1d8969b837c73. Raw generations, Boa/CPython diagnostics, training traces, and bootstrap tables are in arcadia-impact/python4-gemma3-27b-aft-logs under runs/20260811T052635Z.

Interpretation limits

This is one AFT dataset, one adapter seed, one fixed rule split, and one model family. Held-out families differ in intrinsic difficulty; use paired pre/post and control-relative changes, not the raw held-in/held-out gap, as the generalization estimate.