Last June, METR caught o3 reward hacking on its RE-Bench and HCAST benchmarks. In a particularly humorous case, o3, when tasked with optimizing a kernel, decided to “shrink the notion of time as seen by the scorer”.

The development of Humanity’s Last Exam involved “over 1,000 subject-matter experts” and $500,000 in prizes. However, after its release, researchers at FutureHouse discovered “about 30% of chemistry/biology answers are likely wrong”.

LiveCodeBench Pro is a competitive programming benchmark developed by “a group of medalists in international algorithmic contests”. Their paper describes issues with the benchmark’s predecessor:

Benchmarks like LiveCodeBench [35] offer coding problems, but suffer from inconsistent environments, weak test cases vulnerable to false positives, unbalanced difficulty distributions, and the inability to isolate the effects of search contamination.

However, the authors assure us that their own test cases are of high quality:

Many problems in our benchmark originate from Codeforces, which uses the Polygon problem-setting platform. Each problem is then rigorously vetted by a team of expert testers—typically drawn from the community’s top 1%, and overseen by at least one coordinator, usually among the top 0.1%. These specialists verify both the soundness and originality of every problem, ensuring it has never appeared elsewhere before. Testers go on to craft extensive “false positives,” designing edge-case and extreme-case inputs that force problem authors to refine their test suites until every flawed or inefficient solution the testers can think of is uncovered. In addition, Codeforces’ celebrated “Hack” feature empowers the community to submit inputs that expose hidden weaknesses in correct-looking solutions that pass the original test set made by problem authors, and any unit test associated with a successful hack is immediately added to the final test set.

Unfortunately, these distinguished olympiad medalists forgot to actually use the codeforces test cases in their benchmark. Their public test set contains a completely different set of cases, which allow some incorrect solutions to pass.^[1]

Terminal-Bench 2 Audit

I was curious just how widespread such issues were, and how good modern LLMs were at detecting them. I decided to run an LLM based audit of Terminal-Bench 2.0.

Terminal-Bench 2.0 is a harder, better verified version Term

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