OpenAI reports a group without fixed price

A finitely generated group has two essentially free probability-measure-preserving actions with different costs: its Bernoulli action has cost strictly greater than one, while a suitable finite-height extension has cost closer to one.

Sources for this record

What was already known

Gaboriau’s fixed-price problem asked whether all essentially free probability-measure-preserving actions of the same group have the same cost. No general counterexample was established in the manuscript’s prior-work account.

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

Gives a negative answer to Gaboriau’s general fixed-price problem.

Limitations

The construction compares specified essentially free actions of one finitely generated amalgamated group; it does not assert that every action has one of those costs.

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