Most of the commercial and open source offerings for hybrid search seem to be using BM25 + vector similarity search based on embeddings. The results are combined using Reciprocal Rank Fusion (RRF).

The RRF paper is impressive in how incredibly simple it is (the paper is only 2 pages): https://plg.uwaterloo.ca/~gvcormac/cormacksigir09-rrf.pdf

A warning that RRF is often not Enough, as it can just drag a good solution down towards the worse solution :)

https://softwaredoug.com/blog/2024/11/03/rrf-is-not-enough

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