On the Biology of a Large Language Model
Lindsey et al., 2025, On the Biology of a Large Language Model (Transformer Circuits Thread)
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Addition
- How does Claude add two-digit numbers like 36 + 59, and what does it say it does?It runs parallel paths: a low-precision path estimating the rough size of the sum (about 92) and a precise path for the last digit (6 + 9 ends in 5), combined into 95. Asked how, it describes the schoolbook carry method instead: its explanation does not reflect its internal mechanism.
- Lindsey et al., 2025, On the Biology of a Large Language Model (Transformer Circuits Thread), Addition
Source
- Jack Lindsey, Wes Gurnee, Emmanuel Ameisen, Brian Chen, Adam Pearce, Nicholas L. Turner, Craig Citro, David Abrahams, Shan Carter, Basil Hosmer, Jonathan Marcus, Michael Sklar, Adly Templeton, Trenton Bricken, Callum McDougall, Hoagy Cunningham, Thomas Henighan, Adam Jermyn, Andy Jones, Andrew Persic, Zhenyi Qi, T. Ben Thompson, Sam Zimmerman, Kelley Rivoire, Thomas Conerly, Chris Olah and Joshua Batson. 2025. On the Biology of a Large Language Model. In Transformer Circuits Thread. https://transformer-circuits.pub/2025/attribution-graphs/biology.html