Claude Mythos 5 redesigns eight quantum circuits, beating the best published gate counts

Anthropic gave Claude plain-language specifications for eight circuits spanning chemistry, optimization, physics simulation and number theory, plus an automated evaluator that checks correctness and scores qubits multiplied by gates. Claude Mythos 5 iterated in a closed loop with no human input between rounds. Besides the modular inversion result, Anthropic says it made the costliest step of a leading quantum optimization algorithm about 12 times cheaper. The work was led by a fellow in Anthropic's STEM Fellows Program with Harvard collaborators and is posted on arXiv. The result follows a long run of human algorithmic gains: estimated Toffoli gates for simulating FeMoco fell from about 50 trillion in 2017 to about 340 million. Modular inversion is the most expensive step in elliptic-curve calculations, so cheaper circuits also lower the estimated quantum resources needed to attack such cryptography. For builders, the setup is a template: a model that writes code, an objective scorer and an automatic checker. Domains with cheap verification are where autonomous agent loops are now producing results beyond published human work.