COINOTAG reported on Oct. 15, 2026 that a Google quantum chip has cut its error rate roughly forty-fold, a development drawing renewed attention to "Q-Day" — the hypothetical point at which a quantum computer becomes capable of breaking the cryptography securing Bitcoin (BTC). The update lands inside a broader research conversation about how much of the BTC supply would sit in a quantum-vulnerable position, and how far hardware remains from any such machine.

In an update issued at 09:30 UTC, COINOTAG noted that the reading is lower than the 6.9 million BTC figure cited in earlier coverage of the topic, and that Glassnode's methodology measures exposure, not coins an attacker could actually reach today.

The chip in question points to Willow, the quantum processor Google's Quantum AI unit unveiled in December 2024. Willow, a 105-qubit device, was the company's first chip to demonstrate error correction "below threshold," meaning its error rate fell by roughly half each time the logical qubit was scaled up — a reversal of the long-standing pattern in which adding physical qubits tends to add noise. That below-threshold behavior is the property researchers look for, because error correction is the technique by which many noisy physical qubits are combined into the reliable logical qubits a machine running Shor's algorithm would require. Google also reported at the time that Willow completed a random circuit sampling benchmark in under five minutes, a task it estimated would take one of today's fastest classical supercomputers on the order of 10 septillion years.

The report touches a recurring concern in Bitcoin research: the network's reliance on the Elliptic Curve Digital Signature Algorithm (ECDSA). A sufficiently capable quantum computer running Shor's algorithm could, in principle, derive a private key from an exposed public key. Older pay-to-pubkey (P2PK) outputs, including so-called Satoshi-era coins, keep public keys directly visible on-chain, which is why they feature prominently in quantum-risk estimates. Address formats that hash the public key leave it hidden until an output is spent, which is one reason exposure measurements concentrate on those older coins. Glassnode, an on-chain analytics firm, has published research measuring how much of the BTC supply is exposed in this sense — a measure of exposure, as the update stresses, rather than a count of coins immediately reachable by an attacker.

Resource estimates for cryptographically relevant quantum machines have been trending lower, even as experts broadly regard such systems as years away. Google researcher Craig Gidney estimated in 2025 that fewer than one million noisy qubits could factor RSA-2048 in under a week, down from the 20 million qubits projected in a 2019 paper he co-authored with Martin Ekerå. Those estimates translate an algorithm's requirements into a hardware budget, which makes their downward revision one of the concrete gauges of the field's distance from a cryptographically relevant machine. The U.S. National Institute of Standards and Technology (NIST) finalized its first post-quantum cryptography standards in August 2024, and Bitcoin developers have floated quantum-resistant address proposals, including the draft BIP-360, which remains at the draft stage.

None of that background changes the report's core datapoint: the latest exposure reading cited in Glassnode-based coverage is lower than the 6.9 million BTC figure referenced previously, and the methodology counts exposure rather than directly accessible coins. For readers following the topic, the observable markers are similarly discrete: Google's next error-correction scaling results, further revisions to the qubit-budget estimates, movement of draft BIP-360 through Bitcoin's improvement-proposal process, and updated Glassnode exposure readings.

This content was first published on COINOTAG: https://en.coinotag.com/google-willow-quantum-bitcoin-q-day