There is a lot of activity in the space, from things like TurboPuffer (proprietary), Postgres extensions like VectorChord and pgvector, to established players like Elastic getting in on the action. Not to mention things like Pinecone.
> what characteristics make for a best in class ai database
As I said before, I think the space is moving too fast on what is "best in class" - see all the vector indexing work that has happened in the last ~6 months or so. Big, centralised vector stores for some applications will have very different profiles to vector stores on the edge/on device, for example.
As mentioned, I'm a big fan of boring technology, so I'm going to happily wait we have a boring "winner".