Contrastive Learning and SBERT Architecture

~45 min read

How SBERT enables efficient sentence comparison with shared-weight siamese encoders, and the contrastive losses used to train it.

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Key points

  • SBERT uses shared-weight siamese encoders so query and documents can be embedded independently, enabling pre-computation and O(n) retrieval
  • MultipleNegativesRankingLoss requires only (query, positive_doc) pairs — other batch positives become in-batch negatives automatically
  • Larger batch size = more in-batch negatives = stronger training signal for MNRL; 64-256 is a good range