vGROUT is a small research codebase for testing whether an activation-space reward-hacking direction can route GRPO updates into deployed or quarantine adapter parameters.

The current evidence is a partial negative for label-free vector routing. The hand-authored activation direction did not beat Haar-random directions as a high-precision routing classifier in the strongest offline checks. The useful mechanism so far is signed-CorDA absorption: in one 4B run, deployment ablation reduced held-out hack rate from 0.759 to 0.218 while solve rate moved from 0.161 to 0.149. That is mechanism evidence, not a deployable operating point.

An accompanying LessWrong write-up. The public evidence summary is in docs/research_notes.md.

This repository is the minimal public extraction of the working core:

src/vgrout/: GRPO loop, routeA/routeV gates, and block-split adapters.
src/small_reward_hacking/: local LeetCode reward-hacking environment.
scripts/verify_*.py: fail-fast invariant checks used by just smoke.
data/pairs/: authored contrastive pairs used to extract v_act.
data/leetcode/: benchmark jsonl files needed by smoke/eval.
data/pools/ and data/pairsets/: small curated artifacts needed by the correctness gates.
docs/research_notes.md: concise public notes matching the write-up.

Quick Start

uv sync
just smoke

just smoke runs the real tiny-model routeA pathway: reward/eval/split invariant checks, adapter mask checks, activation-direction extraction, routing from pooled activations, masked GRPO, and deployment ablation.

Useful variants:

just smoke-vanilla
just smoke-routeA
just smoke-absorb
just smoke-scorda

Main Hypothesis

Prior gradient-routing work routes updates using labels. vGROUT asks whether a synthetic activation-space direction can replace those labels: score each rollout by pooled bottleneck activations dotted with v_act, then update the deployed block, quarantine block, or both.

The decisive comparison is real v_act against a Haar-random direction while watching quarantine update mass as a confound.

Status

The present result is not a clean success:

oracle-labelled rollout directions show a real linear signal;
hand-authored oracle-free pairs do not reliably align with that signal;
signed-CorDA absorption partially localizes hack capability without routing.

The code is intentionally fail-fast research code. Missing files, stale assumptions, and invalid configs should crash loudly.