In plain words: Instead of splitting a document into pieces and embedding each alone, this runs the document through a long-context model, then cuts it just before averaging word signals into vectors. The pieces keep surrounding context and beat separately embedded chunks on retrieval tests, without training.
Abstract
Many use cases require retrieving smaller portions of text, and dense vector-based retrieval systems often perform better with shorter text segments, as the semantics are less likely to be over-compressed in the embeddings. Consequently, practitioners often split text documents into smaller chunks and encode them separately. However, chunk embeddings created in this way can lose contextual information from surrounding chunks, resulting in sub-optimal representations. In this paper, we introduce a novel method called late chunking, which leverages long context embedding models to first embed all tokens of the long text, with chunking applied after the transformer model and just before mean pooling - hence the term late in its naming. The resulting chunk embeddings capture the full contextual information, leading to superior results across various retrieval tasks. The method is generic enough to be applied to a wide range of long-context embedding models and works without additional training. To further increase the effectiveness of late chunking, we propose a dedicated fine-tuning approach for embedding models.
Michael Günther, Isabelle Mohr, Daniel James Williams, Bo Wang, Han Xiao
arXiv:2409.04701 · cs.CL, cs.IR · submitted Sep 7, 2024 · updated Jul 7, 2025
abstract · pdf · html · 11 pages, 3rd draft
https://weaviate.io/blog/late-chunking
https://jina.ai/news/late-chunking-in-long-context-embedding...
The late chunking idea originates from ColBERT, an embedding technique from 2020 https://arxiv.org/pdf/2004.12832