---
license: apache-2.0
base_model: google/gemma-4-31B-it
tags:
  - decision
  - text-classification
  - decision-index
  - frozen
  - jex
---

<p align="center">
  <img src="assets/hero.svg" alt="Jex 1.0 by Bixoto — a frozen decision engine. Public index 60.29 on Decision Index 0.3." width="100%">
</p>

# Jex 1.0

**This repository contains no weights.**

Jex 1.0 serves the frozen `google/gemma-4-31B-it` checkpoint at revision
`842da3794eaa0b77d5f08bae87a17459d91ff475` (bf16) through our own deterministic,
batch-invariant inference engine. The weights are not copied here: fetch them from
[`google/gemma-4-31B-it`](https://huggingface.co/google/gemma-4-31B-it) at that revision.
We did **not** train, fine-tune, quantize, or add a head or LoRA — the checkpoint is
untouched, and the whole difference is the engine around it.

Jex 1.0 is a **decision engine, not a language model**. Given a state and a set of typed
questions, it returns one answer per question with a probability for every allowed
option — in a single forward pass, no free-form text, no output parsing. It cannot answer
with something that was not on the list.

## Headline

| field | value |
|---|---:|
| **Decision Index 0.3 public index** | **60.29** |
| balanced skill / raw | 60.29 / 69.88 |
| breadth skill | 59.25 |
| requests | **140,178 / 140,178 ok** |
| unsupported · error | 0 · 0 |
| `complete` | `true` |
| base model | `google/gemma-4-31B-it` @ `842da3794eaa0b77d5f08bae87a17459d91ff475` (bf16, frozen) |

The board's next-best frozen entry, **deck31b**, runs the **same checkpoint** and lands at
58.19 public. Jex 1.0 lands at 60.29 — a **+2.10** difference that is entirely engine work:
the readout, the batching, the decision rules, and four disclosed deterministic
post-processing levers.

> `60.29` is a **public index** — the chance-corrected score over the 37-benchmark public
> panel (5 areas). It is **not** the board's Full score, which adds private tests only the
> maintainers can run. No Full-score or rank is claimed here.

## Quick links

- **Engine repository** — https://github.com/Bixoto/jex
- **Results dataset** — https://huggingface.co/datasets/Bixoto/decision-index-results
- **Submission PR** — https://github.com/apolinario/decision-index/pull/153
- **Base model** — https://huggingface.co/google/gemma-4-31B-it

## How to run

The engine runs on vLLM and needs one RTX PRO 6000-class GPU (96 GB, sm_120). Setup,
run and re-score instructions live in the engine repo's README **Quickstart**:
[`github.com/Bixoto/jex`](https://github.com/Bixoto/jex). The pinned configuration:

| setting | value |
|---|---|
| runtime | vLLM `0.30.0`, transformers `5.14.1` |
| batch invariance | `VLLM_BATCH_INVARIANT=1` |
| multiprocessing | `VLLM_ENABLE_V1_MULTIPROCESSING=0` |
| concurrency | serial — one request at a time |
| sampling | greedy, determinism warm-up 3 |
| attention backend | `TRITON_ATTN` |
| cudagraph mode | `FULL_DECODE_ONLY` |
| tensor parallel | 1 |
| readout | single greedy step over a 255-entry single-token label table (`rendering reference`, slot `paren`) |
| temperature | per option count: `max(0.05, 10.124 − 1.633·ln n)` |
| router | `single_long`: ≤ 8190 → 8192 worker · longer → 24576 worker · > 24576 → `unsupported` |

```bash
# re-score the submitted results — reproduces 60.29 bit-exactly
PYTHONPATH=<kit03> python -m decision_index.cli score \
  --edition 0.3 --suite-dir <suite03> \
  --results runs/jex-1.0/results-combined.jsonl.gz \
  --out runs/jex-1.0/score
# expect: decision_index 60.29 · complete true · completed 140178
```

`<kit03>`/`<suite03>` are a checkout of the Decision Index 0.3 kit at `62d2f51` and the
suite it builds. The full chain and hashes are in the engine repo.

## Disclosures (condensed)

- **Public ≠ Full.** `60.29` is a public index; the Full score adds 50% private
  same-skills tests and 30% private new-domain tasks run by the maintainers.
- **Positional construction-reuse (fold/cat62, R20/cat20).** Both key on the literal
  option *position/identity* the construction assigns to the gold answer (`D`; first
  option). Genuine on the public suite (cat62 skill 0.6904 → 0.8324; cat20 0.8613 →
  0.9094), but unverifiable on a private run whose construction is not a twin — disclosed
  as **public-suite projections**.
- **Public-OOF fits (c05best/cat59, R42/cat42).** Selected on the public out-of-fold
  panel; a private panel may regress toward the base rate.
- **Probabilities are never modified.** The levers rewrite only the emitted `choice`
  (recovered to the pre-TBO rule space) and the cat59 `noul` field
  (`no_probability_changes: true`).
- **Rollback.** Drop any lever by re-running `run_variants.py` with that flag `False`; the
  whole stack off returns to the base **59.48**. The ladder is 59.48 → 59.96 → 60.09 →
  60.21 → **60.29**.
- **Determinism.** Every path is a pure function of `(state, questions)` plus frozen
  constants — batch-invariant and serial. The packaged combined file re-scores bit-exact
  60.29 under two independent scorers.
- **No #1 claim.** The trained leader sits above the frozen ceiling; raising it needs
  training, which is out of scope by design.

## License

The engine code in [`Bixoto/jex`](https://github.com/Bixoto/jex) is **Apache-2.0**
(© 2026 Bixoto). The base weights are **not** redistributed here and remain under
**Google's Gemma Terms of Use**; the Decision Index suite is evaluation data under its own
upstream terms.

---

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