From the official release notes and blog. Every item points at the concepts worth re-reading.
NEAREST BY is a SQL join that finds, for each row on the left, the k closest rows on the right by vector similarity or distance, either EXACT or APPROX. It runs in Photon with a fused operator, and APPROX queries can use an IVF index stored as a liquid-clustered Delta table. The post does not state a release stage, so availability needs checking against the documentation.
AI Search can now index and filter struct and map columns. It can also run filter-only queries that return rows matching a filter without vector or keyword retrieval.
The ai_search function can now retrieve from Lakebase synced tables that have Lakebase Search enabled, as well as from AI Search indexes. A call adds a lakebase_search knowledge source, and it can be combined with vector_search sources in the same call. The release notes label this Beta.
Nothing of that kind yet.