Reasoning & knowledge

BIG-Bench Hard (BBH)

by Suzgun et al. (from Google's BIG-Bench)

What is BIG-Bench Hard (BBH)? BIG-Bench Hard (BBH) is a suite of 23 tasks from Google's BIG-Bench on which earlier language models did not beat the average human rater. Its paper showed that chain-of-thought prompting closes much of that gap.

Page last updated 2026-10-17 · Evals Review

Editor note

23 BIG-Bench tasks on which earlier language models did worse than the average human rater. The paper showed chain-of-thought prompting let Codex pass the human average on 17 of the 23, so scores depend heavily on the prompting method.

What it tests
Multi-step reasoning across varied puzzle-style tasks.
Original source
github.com/suzgunmirac/BIG-Bench-Hard
Last updated
Repo last commit 2024-06-25
License
MIT

Facts come only from the linked source (checked 15–16 Oct 2026). Credit belongs to the creators.

When to use BIG-Bench Hard (BBH)

  • You want a widely reported multi-step reasoning score for base or smaller models.
  • You want to compare prompting methods: the repo ships chain-of-thought prompts for every task.

Limitations

  • Frontier models now score high, so it separates them less than newer sets.
  • Scores swing with prompting (few-shot vs chain-of-thought); report the method.

How to run it

  1. Get the task files from the repository's bbh folder and prompts from cot-prompts.
  2. Run the model with the few-shot or chain-of-thought prompts and score exact match against the task answers.

Notable results

  • Paper: with chain-of-thought prompting, PaLM beat the average human rater on 10 of 23 tasks and Codex on 17 of 23. [Paper (arXiv)]

Sources

Everything above comes from the sources listed, read on 15–16 Oct 2026. Commands are copied from the official instructions; check the source for changes.

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