How LLMs and coding tools work8 min read

Lost in the Middle: How Language Models Use Long Contexts

Nelson F. Liu, Kevin Lin, John Hewitt, Ashwin Paranjape, Michele Bevilacqua, Fabio Petroni, Percy Liang · 2023 · Transactions of the Association for Computational Linguistics 12 (2024), 157–173

Models find information at the start and end of a long input far more reliably than information in the middle — and a bigger context window does not fix it.

Read the paper ↗doi:10.1162/tacl_a_00638 ↗

The short version

→Move the one relevant document around inside a long prompt, change nothing else, and accuracy swings dramatically.
→The shape is a U-curve: best when the needed information is at the beginning or the end, worst in the middle.
→This held on explicitly long-context models too — having room for the tokens is not the same as using them.
→A context window is a capacity, not a promise. Where you put things inside it is a design decision.

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