Hi @sashank06, sorry I misunderstood the question.
As far as I understand from the source code 1 class LegacyIndex refered to original index use in the RAG/DPR papers, while class HFIndexBase allows us to use custom datasets (there’s dataset argument).
Therefore, according to above quote, I understand “exact” and “compressed” are subtypes of “legacy”. I may misunderstood, and would be great if @lhoestq can help clarify here