The situation with AMD is a bit complicated. Basically, there was an antitrust lawsuit led by AMD years ago, and as part of the settlement, Intel and AMD would share patents to allow collaboration. I can’t recall the actual specifics though.

As for patents, I don’t, but someone else here linked in the one for FMA[0]. It’s a bit more complicated than just an API, but it seems broad enough that anything implementing that API would be covered. But IANAL.

[0]: https://patents.google.com/patent/US7499962