Retrofitted LLM can count the letter 'i's in 'artificial intelligence' | Nature

Email Bluesky Facebook LinkedIn Reddit Whatsapp X Save article View saved research Strawberry contains the letter ‘r’ three times, but when asked, many large language models (LLMs) answer that the letter appears twice. This happens because most LLMs encode words as ‘tokens’ that represent sequences of letters. LLMs that operate in this way can achieve excellent performance, but they cannot access the individual characters in each word, which are encoded as binary sequences called bytes. Writing in Nature , Minixhofer et al . 1 now report an approach called byteification that retrofits token-based LLMs to operate at the byte level. The authors show that byteified models can achieve competitive performance while retaining the ability to read individual characters. Access options Access through your institution Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription 27,99 € / 30 days cancel any time Learn more Subscribe to this journal Receive 52 print issues and online access 185,98 € per year only 3,58 € per issue Learn more Rent or buy this article Prices vary by article type from $1.95 to $39.95 Learn more Prices may be subject to local taxes which are calculated during checkout doi: https://doi.org/10.1038/d41586-026-03059-2 References Minixhofer, B. et al. Nature https://doi.org/10.1038/s41586-026-11111-4 (2026). Article Google Scholar Sennrich, R., Haddow, B. & Birch, A. in Proc. 54th Ann. Meet. Assoc. Comput. Linguist . 1715–1725 (2016). Cosma, A., Ruseti, S., Radoi, E. & Dascalu, M. in Proc. 2025 Conf. Empir. Meth. Nat. Lang. Proc . 28252–28263 (2025). Pagnoni, A. et al . Proc. 63rd Ann. Meet. Assoc. Comput. Linguist . 9238–9258 (2025). Download references Reprints and permissions Competing Interests The authors declare no competing interests. Related Articles Read the paper: Retrofitting language models to operate over bytes Expert-level test is a head-scratcher for AI Algorithm that gets ‘under the hood’ of AI models could effectively steer their responses See all News & Views Subjects Machine learning Latest on: Machine learning The science of superintelligence and why AI is still a useful word News Explainer 07 OCT 26 OpenAI posts 700 maths preprints online: mathematicians are up in arms News 07 OCT 26 AI could undermine scientific independence in subtle ways Correspondence 06 OCT 26 Jobs Assistant or Associate Professor of Cell Biology Department of Cell Biology at the University of Virginia School of Medicine invites applications for Assistant or Associate Professor of Cell Biology Charlottesville, Virginia University of Virginia Recruitment Announcement for High-Level Talent at the Center for Agricultural Microbiology Join HZAU's global faculty team to advance research with competitive benefits. Wuhan, Hubei (CN) Huazhong Agricultural University (HZAU) Open-Rank Faculty Position in Theoretical Biology The Department of Biological Sciences seeks an outstanding individual for an open-rank faculty position in Theoretical Biology. Nashville, Tennessee Vanderbilt University Department of Biological Sciences Proteomics Specialist Build the science that shapes the future of human health. Application closing date: 08 November 2026 Join a place where ambitious science thrives... Milan (IT) Human Technopole Tenure-Track Professor/Associate Professor/Assistant Professor The University of Hong Kong We are seeking a motivated Tenure-Track Professor/Associate Professor/Assistant Professor to join our Department of Pha... Hong Kong (HK) The University of Hong Kong