New Fable5/Opus4.8 harness called "Schema" claims 99% on ARC-3 [R]

Overview

Schema, the harness we introduce today, reaches 99% on the ARC-AGI-3 Public set using Claude Opus 4.8 and Fable 5, and 95.35% using GPT-5.6 Sol.

It does not change the underlying model weights. Instead, it changes the process around them: how observations are turned into a working model of the game, how predictions are tested against the interaction history, and how plans are executed and revised.

Scoring Methodology

Both scores come from a fixed fallback rule:

• Opus 4.8 and Sol xhigh run first
• Games scoring below 80 are rerun with Fable 5 and Sol max, respectively
• The higher per-game score is retained

Links and Context

The harness is available at: https://schema-harness.github.io/

The president of ARC Prize tweeted this saying "Looks cool - need to dig into it."

I'm not affiliated with ARC Prize, or with this team. I'm posting this to try to bring back technical discussions to this community.