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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Introductory Example: Multi-step Reasoning
- How does Claude 3.5 Haiku complete “the capital of the state containing Dallas is”?Partly by genuine two-hop reasoning: “Dallas” features activate “Texas” features, which combine with “say a capital” features to promote “Austin”; a direct Dallas → Austin shortcut also exists. Swapping in “California” features in place of “Texas” makes the model say “Sacramento”.
Two-hop circuit, simplified (after Lindsey et al.’s attribution graph) - Lindsey et al., 2025, On the Biology of a Large Language Model (Transformer Circuits Thread), Introductory Example: Multi-step Reasoning
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