---
title: MMBench2 · Hallucination Signals vs True Error
emoji: 🔭
colorFrom: indigo
colorTo: gray
sdk: gradio
sdk_version: 6.17.3
app_file: app.py
python_version: "3.10"
startup_duration_timeout: 40m
pinned: false
license: mit
short_description: Hallucination signals vs. true world-model rollout error
---

# Hallucination signals vs. true rollout error

Interactive companion to *"Hallucination in World Models is Predictable and
Preventable"*. Drive a 350M-parameter world model with the keyboard and watch four
signals get scored, live, against the error the model actually makes.

| signal | what it measures | sees the future? |
|---|---|---|
| `u_r` | motion-normalized tokenizer round-trip residual | no |
| `u_f` | denoising-trajectory instability | no |
| `u_s` | motion-normalized inter-seed variance | no |
| **`WAV`** | **inverse-dynamics rollout divergence (ours)** | **yes** |

**Target.** Pearson *r* against the mean distance between an open-loop rollout
driven by the *ground-truth* actions and the real trajectory, unnormalized.

The target is deliberately not motion-normalized. `u_r` and `u_s` are themselves
divided by a motion term, so scoring them against a motion-normalized target
shares that 1/motion factor and manufactures correlation. Measured offline over
120 trajectories, switching the target from normalized to unnormalized moved
`u_r` from 0.715 to 0.394 and `u_s` from 0.818 to 0.490 while `u_f` *rose* from
0.591 to 0.705 — it reversed the ranking.

**WAV is not a peer of the `u_*` signals** and the UI keeps it apart. It infers
the action from the real next frames, so it is an offline audit measurement, not
a runtime predictor: its ceiling is 1.0, reached by using the true action instead
of the inferred one. Over 150 trajectories on 6 tasks it scores **0.959**, with
the label-free estimate landing within **1%** of the labelled measurement.

## Controls

| input | action |
|---|---|
| arrows / WASD | actions (dimensions depend on the task) |
| Space, or click the frame | pause |
| R | reset the episode |
| dropdown | switch task |

Correlations need a few rollout samples before they appear — the multi-step
rollout is scored with a lag, since the real frames it is compared against have
to arrive first.

## Notes

GPU time is allocated in bounded windows. The session survives a window ending,
so the step counter keeps climbing and your accumulated statistics are not reset.

Task domains whose native dependencies fail to build are hidden from the dropdown
rather than breaking the app; the startup log lists any that were dropped.

Configurable via Space variables: `WAV_EVERY`, `WAV_HORIZON`, `WAV_HORIZON_LONG`,
`GPU_DURATION`, `WM_VARIANT`.