Chroma doesn't seem to be a real DB, it's rather a wrapper around tools like hnswlib, DuckDB or Clickhouse. Qdrant is way more mature - it has its own HNSW implementation with some tweaks to incorporate filtering directly during the vector search phase, supports horizontal and vertical scaling, as well as provides its own managed cloud offering.

In general, Qdrant is a real DB, not a library and that's a huge difference.

What does Chroma lack? Their APIs seem pretty much the same to me.

I've tried both Chroma and Qdrant. I don't think Chroma lacks that much. Definitely newer, but is also a great product. I think cloud support coming Q3 2023