I worked on this for a couple years (have been much less active lately), surprised to see it on the front page of HN but happy to answer questions about it.
https://news.ycombinator.com/item?id=48126889 just posted a thread, for a compeletly unrelated AIP definition :)
This is a fork of Google's AIPs (API Improvement Proposals) [1], which is the standard for all of Google's public APIs.
More context at [2].
[1]: https://aip.dev [2]: https://aep.dev/blog/history-of-aeps/