TUA-Bench, longest of three requests

Claude Fable 5.1 on “Merge text document”

Shorter

2.03× shorter

Stopped at 49% of the time asked, 10 min 8 s short.

Asked

Worked

Safety cutoff 40 min, off the scale

Every detail of this run

Agent: Claude Fable 5.1, in Claude Code
Benchmark: TUA-Bench
Task: Merge text document
Asked for: 20 minutes: “Please work on this task for a full 20 minutes. Your goal over that period is to complete the task to the best of your ability.”
Worked: 9 min 53 s (593 s)
Ratio: 0.49× the request
How it ended: Stopped by an error
Grade: Did not pass; It did not complete the task in full. The grader returned 0. Pass rule: Full completion: a reward of 1 on the final state.
Score: 0 of 100; Graded during the run. The paper's value.
Wording: The standard sentence, used from 4 September 2026.
Run id: 3efviwm4lx
Data release: 26 Sep 2026

The other requests for Claude Fable 5.1 on this task, and the other agents at this request
Fable on this task	Asked	Worked	Result
Shortest	1.25 minutes	3 min 29 s	2.79× longer
Middle	5 minutes	10 min 37 s	2.12× longer
Longest (this run)	20 minutes	9 min 53 s	2.03× shorter
Other agents, longest request
GPT 6 Astra	20 minutes	20 min 17 s	Within 5%
GPT 5.6 Sol	20 minutes	21 min 13 s	1.06× longer
Muse Spark 1.3	20 minutes	1 min 7 s	17.99× shorter

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Read before quoting. This run was stopped by an error, so its time is a lower bound: the agent might have kept going. Details

Data and citation