Gemma 4 12B-it — hand-edited for one EN→IT tense choice (weight-space programming)

A constructive, tightly-scoped weight edit: a frontier model (Claude Opus) rewrote a handful of MLP neurons in Gemma 4 12B-it so that, when translating English into Italian, it chooses imperfetto + da instead of the trapassato calque only when the past action was still ongoing — and keeps the trapassato when the period was really over (where the imperfetto would change the meaning).

He had been hiding in the attic for months when the soldiers found him. base: «Si era nascosto in soffitta per mesi quando i soldati lo hanno trovato.» edited: «Si nascondeva in soffitta da mesi quando i soldati lo trovarono.»

Only 6 tensors in layers 31 and 34 are touched (4 neurons each). Everything else is bit-identical to the base. General translation quality (COMET on FLORES) is unchanged.

Full write-up, data and protocol

• GitHub: https://github.com/ValerioDolci/frontier-weight-edit (code, data, blind-judge verdicts, baselines, tests).
• This is the constructive half of the project. Its companion is a deliberately tampered model published for awareness — same technique, opposite intent: https://huggingface.co/Feyd89/Qwen3.8-27B-TAMPERED-brand-implant-experiment

Inspired by / cites

MIT CSAIL — Sparks of Weight-Space Programming (Takehi, Teoh, Zhang, Khattab, Nov 2026): https://rikiyat.github.io/blog/weight-space-programming/ — a frontier model reads and edits another model's weights directly, without training. This project applies the idea to a model used daily and to a preference shift rather than a failure fix.

Files

• gemma-4-12B-it-tense-edit-Q4_K_M.gguf — runnable locally (Ollama / LM Studio / llama.cpp).
• edit.npz + manifest.json — the exact edit (only the changed neuron slices), with sha256 of the base and edited tensors and the pinned base revision. Apply it to google/gemma-4-12B-it with scripts/apply_edit.py from the GitHub repo to reproduce this model bit-for-bit.

License / provenance

Derivative of google/gemma-4-12B-it, subject to the Gemma Terms of Use. Research artifact.