Schwartz Releases BootLoops 1.0, an Open-Source LLM Harness for Science

Anthropic on October 1, 2026 published Claude-shaped science, a guest post by theoretical physicist Matthew Schwartz describing BootLoops, an open-source toolkit he built with Claude for exact calculations in quantitative science. BootLoops 1.0 was released publicly the same day under the MIT License. Schwartz writes that he began the project when Anthropic released Claude Fable 5 in Summer 2026, after an earlier experiment, described in his Anthropic post Vibe Physics, in which he used Claude Opus 4.5 as a research assistant in December 2025.

His first assignment for the new model was to port and unify methods from his scattering-amplitudes papers and the adjacent literature into one framework built on the S-matrix bootstrap and the semi-numerical bootstrap, complementary approaches that pin down an amplitude through physical constraints and high-precision numerical evaluation until one exact answer remains. In particle physics, scattering amplitudes provide the theoretical link between collision debris at the Large Hadron Collider and the particles a collision produced, and Schwartz writes that a single frontier Feynman integral can occupy a research group for years.

He reports that Claude reproduced…