Anthropic: Claude Mythos 5 Autonomously Designs Quantum Circuits, One Design's Gate Count Cut to 1/17

What happened

According to Anthropic's official research blog post of October 16, Claude Mythos 5 completed eight quantum circuit design tasks in a closed-loop process: the model wrote Python circuit-design code, an automatic evaluator verified and scored it, and the model iterated with no human intervention. In seven of the eight tasks, the resulting designs reduced both Toffoli gate counts and qubit counts.

The standout result was modular inversion in elliptic-curve point addition: after a 53-hour single run, the model produced the first branch-history-free reversible divsteps implementation; one design used 12% more qubits than the smallest published design while cutting the gate count to 1/17 of it. Anthropic also released an arXiv preprint. According to aitoolsrecap's October 17 report, Claude beat published quantum circuit designs on all eight tasks, cutting gate counts by up to 17x.

Key facts

1. Published: October 16, 2026 (Anthropic's official research blog)
2. Scope: Eight quantum circuit design tasks, closed-loop automatic iteration, no human intervention
3. Improvements: Seven tasks reduced both Toffoli gate counts and qubit counts
4. Best single result: Modular-inversion design's gate count cut to 1/17 of the smallest published design
5. Paper: An arXiv preprint was released alongside