Quantum threat draws nearer: Threshold to break Bitcoin falls to 813 logical qubits

God doesn't play dice. Except that Bitcoin has no choice but to play. Google Quantum AI had already dropped the estimate to around 1,200 logical qubits at the end of March, a tenth of the quotes before 2026. Since then, the race has not stopped: as of August 31, the public ranking ecdsa.fail, which continuously tracks the most economical circuit to break the secp256k1 elliptic curve used by Bitcoin and Ethereum, showed a new floor of 813 qubits logical. A drop of 65% compared to the 2,330 qubits estimated in 2017, according to Circle calculations.

ecdsa.fail, the open competition that is nibbling away at the threshold

The principle: a public competition, hosted by Eigen Labs, where researchers and artificial intelligence agents submit quantum circuit optimizations and compete for the best score on an indicator called “qubit-Toffoli product”.

Each marginal improvement slightly pushes back the theoretical threshold needed to threaten a Bitcoin key. None of this mechanically brings a machine capable of exploiting it any closer: Google's Willow processor currently caps at 105 logical qubits, and QuEra's roadmap aims for barely more than 1,000 logical qubits by 2029. The gap remains real. But it tightens on both sides at once, the available power climbing while the cost of the attack falls.

Circle releases its own thermometer

It is in this context that Circle, the issuer of the stablecoin USDC, published at the end of August a new public monitoring tool, the Quantum Tracker, which superimposes on the same graph the line of logical qubits demonstrated in the laboratory and that of the attack threshold required against ECDSA. Each point on the graph links to its primary source, allowing researchers and security teams to track the gap without relying on a single press release. Circle's Arc network already supports SLH-DSA, a post-quantum signature scheme validated by NIST, while maintaining ECDSA in parallel while a transition standard is imposed on the entire ecosystem.