Agents' Last Exam, shortest of three requests

Claude Fable 5.1 on “Build a reusable HST ACS/WFC visit-reduction pipeline”

Longer

9.54× longer

Worked 854% past the request, 42 min 42 s over.

Asked

Worked

Safety cutoff 2 h 40 min, off the scale

Every detail of this run

Agent: Claude Fable 5.1, in Claude Code
Benchmark: Agents' Last Exam
Task: Build a reusable HST ACS/WFC visit-reduction pipeline
Asked for: 5 minutes: “Please work on this task for a full 5 minutes. Your goal over that period is to complete the task to the best of your ability.”
Worked: 47 min 42 s (2,862 s)
Ratio: 9.54× the request
How it ended: Stopped by an error
Grade: Did not pass; It did not pass the task's checker in full. The grader returned 0. Pass rule: Full pass: a checker score of 1.
Score: 0 of 100; Nothing to grade, counted as 0. The paper's value.
Wording: The standard sentence, used from 4 September 2026.
Run id: ms4ws7tlxj
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 (this run)	5 minutes	47 min 42 s	9.54× longer
Middle	20 minutes	18 min 8 s	1.10× shorter
Longest	80 minutes	38 min 10 s	2.10× shorter
Other agents, shortest request
GPT 6 Astra	5 minutes	8 min 19 s	1.66× longer
GPT 5.6 Sol	5 minutes	17 min 37 s	3.52× longer

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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