The steering committee charter states "Each year, when Contribution Seat terms begin, the Steering Committee will vote on an exact formula and procedure for determining allocation for the following year."
For the February 2023 to January 2024 term, the contribution formula was contributions (being a review, commit, discussion, issue or PR on GitHub) attributed to a Contributing Company, as measured by DevStats, and the D'Hondt method of allocation of seats.
Attribution is done using the cncf/gitdm developer affiliation files. Changes to attribution can be made by Pull Request to that repository.
The method and results for the previous term are published here.