Today, we’re announcing metadata pre-filtering for Amazon S3 Vectors, which delivers higher recall on filtered queries by evaluating your metadata filter before the similarity search. You can filter on attributes such as tenant, category, status, or time, and pre-filtering adds prefix matching with $startsWith for paths, URLs, and hierarchical keys. Each vector carries up to 2 KB of filterable metadata, and a single query supports up to 100 filter constraints. There is no additional cost, no re-ingestion, and no change to your queries.

Most applications never search a whole index. They search the part of it that belongs to a particular user, account, or category, and they express that scope as a metadata filter. Semantic search, retrieval-augmented generation (RAG), and agentic applications all need the same thing from a filtered query: a similarity search that covers the vectors matching the filter, and returns the closest of them. With pre-filtering, a filtered query returns more of the relevant matches your index contains, giving you higher recall on filtered searches.

Common use cases
Pre-filtering applies wherever results have to be both relevant and correctly scoped:

  • Legal and professional services: A law firm or e-discovery platform searches documents scoped to a single client, and with $startsWith narrows further by matter number, folder path, or document ID prefix. A single client is a small share of a firm-wide archive, and filters this narrow are where pre-filtering improves recall most.
  • Financial services: An investment research platform searches analyst notes, filings, and call transcripts scoped by issuer, document type, and publication date.
  • Media and entertainment: A streaming service filters by content rating and regional licensing before the semantic search, finding similar titles restricted to G and PG content licensed in one territory.
  • Agentic applications: An agent working within a user’s session filters on fields such as owner, document set, and timestamp so its searches cover the material relevant to the task at hand. Higher recall means more of that material reaches the agent, which improves task reliability

How pre-filtering works
Each vector in an S3 Vectors in

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Source: AWS Blog (Published: Wed, 30 Sep 2026 20:03:34 +0000). Read the full article on the original site.