OpenAI reports a four-dimensional Borel rigidity counterexample

There are closed connected aspherical topological four-manifolds with word-hyperbolic common fundamental group that are homotopy equivalent but not homeomorphic.

Sources for this record

What was already known

Borel rigidity was established in dimensions at most three and for many groups in dimensions at least five. Four-dimensional applications required additional good-group conditions; the homeomorphism-existence question remained open for the stated hyperbolic-group setting.

AI involvement AI-led

OpenAI credits itself as manuscript author and states that its internal frontier model produced the results in this release. Individual human input is not detailed enough to establish task-only autonomy.

OpenAI is named as author on the manuscript, and its release attributes the results to an internal frontier model. The individual human input is not detailed enough to establish autonomy.

Importance Major

Disproves the homeomorphism-existence form of the Borel conjecture in dimension four.

Limitations

This is nonexistence of any homeomorphism between the two manifolds, not merely failure to realize one prescribed homotopy equivalence.

Technical verification Reported

Reported is the default when evidence for a higher level is insufficient. The OpenAI-authored manuscript reports and argues the result, but the reviewed sources do not document a completed check of the full assessed claim.

Human understanding Few

Few is the default when evidence for a higher level is insufficient. No named person is documented as explaining the central argument for this assessed contribution.

Correction and publication history

2026-10-18 · publication

Primary manuscript, attribution, and prior-work review for non-notifying local inclusion; technical verification remains Reported.

Read this published revision