Foundations

Embedding

A numerical vector that captures the semantic meaning of a piece of content.

An embedding is the output of a neural network that maps text, images, or audio into a fixed-length vector. Similar inputs produce vectors that are close together in the embedding space — 'invoice' and 'bill' end up near each other; 'invoice' and 'lasagna' do not.

Embedding models (text-embedding-3, Cohere embed, BGE, E5) are the workhorse behind semantic search, RAG, clustering, and classification. They are 100–1000x cheaper than LLM calls, so it is common to embed millions of documents up front.

Choice of embedding model matters more than most teams realize. Domain-specific models (legal, biomedical, code) often beat general-purpose ones for their niche.

Key points

  • Typical dimensions: 384, 768, 1024, 1536, 3072
  • Higher dimensions ≠ better — often the opposite for smaller corpora
  • Multilingual models cost 5–10% more but eliminate translation preprocessing
  • Re-embedding on model upgrade is a real operational cost

Common use cases

Semantic search
RAG document retrieval
Clustering and topic modeling
Zero-shot classification

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