Anthropic says Claude beat top quantum circuit designs

Anthropic said on October 16, 2026, that its Claude Mythos 5 model, working mostly on its own, designed quantum circuits that beat the best published designs, in some cases by "an order of magnitude or more." The company said the model was given plain-language specifications for eight circuits from chemistry, optimization, physics simulation and number theory, along with an automated evaluator that checked and scored each design.anthropic.com

The findings matter because current quantum computers have only hundreds to thousands of noisy qubits. Cheaper circuits lower the hardware needed for useful applications, and Anthropic argues this could mean practical machines "arrive sooner than previously anticipated".anthropic.com

Fewer gates and qubits

A companion paper, "Discovering state-of-the-art quantum circuits with large language models," was posted to arXiv on October 15. It describes an evolutionary framework in which Claude proposes circuit-generating programs and an independent evaluator checks them for correctness and cost. In seven of the eight tasks, the circuits it found cut both Toffoli gate counts and qubit counts compared with the state of the art. The paper scores each design by Toffoli count multiplied by peak qubit count, a measure it calls TQ-cost.arxiv.org

Andi Gu led the work through Anthropic's STEM Fellows Program, with mentoring from Anthropic quantum physicist Alek Kemeny. He worked with Susanne Yelin of Harvard and Mikhail Lukin of Harvard and QuEra Computing.anthropic.com

One result was a decoder for decoded quantum interferometry, a candidate quantum optimization algorithm. The new design used 440,000 Toffoli gates and 1,837 qubits, which is 12 times fewer Toffolis than the Reed–Solomon baseline. That baseline is a construction from Google.unite.ai+1

A new route to modular inversion

The eighth task produced a new reversible design for prime-field modular inversion. This is the most expensive step in the elliptic-curve arithmetic used by quantum algorithms for the discrete logarithm problem. Claude worked on it for 53 hours. Human input was limited to the initial brief and occasional prompts to think more broadly.anthropic.com

The model adapted divsteps, a classical method that had been impractical in reversible form because it needed a large stored record of past steps. Claude derived a rule that recovers that record from the numbers themselves. It checked the rule with simulations and a formal proof in the Lean language, producing what Anthropic called "the first reversible implementation of divsteps with no stored branch history". One design in the resulting family uses 12% more qubits but 17 times fewer gates than the smallest previous circuit.anthropic.com

Building on years of reductions

Anthropic described the work as part of a longer trend of cutting costs through algorithm design. For example, estimates for simulating the FeMoco catalyst fell from about 50 trillion Toffoli gates in 2017 to about 340 million, mostly by redesigning circuits rather than improving hardware. The release came after QuEra reported in August that Claude wrote software that restored a quantum computer's laser system in 695 of 700 trials.thequantuminsider.com+1

The paper's authors say their results "open the door for evaluator-guided LLM co-design of new algorithmic structures for quantum computation".arxiv.org