Quantum computing has been a significant concern in the discussions surrounding Bitcoin security. Recently, a leading researcher from ARK Invest has expressed increased confidence regarding this issue.
Lorenzo Valente, the Director of Research for Digital Assets at ARK, noted that he feels more hopeful about Bitcoin’s ability to implement a quantum-resistant solution before the so-called “Q Day.” This term refers to the hypothetical point when a quantum computer could potentially break the cryptographic defenses protecting Bitcoin addresses.
Valente’s remarks, made in mid-October 2026, represent a shift from his perspective in mid-2025. His current viewpoint aligns with a white paper that ARK collaborated on with Unchained, released on March 12, 2026.
This white paper outlines five phases of quantum risks to Bitcoin, asserting that the danger evolves gradually rather than appearing suddenly.
The paper positions quantum risk as a long-term challenge, rather than portraying Q Day as an abrupt event that could annihilate Bitcoin within hours.
This extended timeline allows developers time to make necessary upgrades to protocols. These upgrades may include post-quantum signature schemes, designed to withstand potential quantum intrusions.
The risk is not merely hypothetical. As of October 11, 2026, around 7.1 million BTC is held in addresses that have publicly exposed keys.
This constitutes roughly 35% of the circulating Bitcoin supply, which is deemed susceptible to attacks utilizing Shor’s algorithm—a quantum method that could theoretically deduce private keys from public ones.
Bitcoin’s security is based on elliptic-curve cryptography (ECC) to verify coin ownership. The public key acts like a padlock visible to everyone, while the private key is the unique key that unlocks it. Traditional computers cannot efficiently reverse-engineer the key from the padlock. However, a sufficiently advanced quantum computer using Shor’s algorithm could potentially do so.
Research indicates that a substantial portion of these vulnerable coins is either seen as lost or kept in addresses that could transition to more secure configurations. Lost coins cannot be accessed by their owners, while coins that can be moved could relocate to quantum-resistant addresses once they are available.
Moreover, it has been found that most Bitcoin addresses utilize hashed public keys, which offer greater resilience against possible quantum threats, as the actual public key remains concealed until the coins are utilized.
Currently, quantum computers operate within what researchers term the Noisy Intermediate-Scale Quantum (NISQ) era. These systems are characterized by their susceptibility to errors and limited capabilities.
Present technology does not pose a threat to Bitcoin’s 256-bit ECC, with experts estimating it could take years or even decades for quantum advancements to reach that level.
Various draft proposals for new output formats are being explored, including BIP-360, which aims to enhance Bitcoin’s defenses against quantum threats.
ARK’s analysis suggests that the Bitcoin ecosystem is aware of these challenges and is ready to implement protective measures. Ongoing discussions in the community indicate that solutions are being developed rather than ignored.
The approximately 35% of Bitcoin supply in exposed addresses warrants attention. Holders who employ older address formats or reuse addresses should be informed about their vulnerabilities, as these coins are most likely to require migration.
Important developments to monitor include whether BIP-360 moves beyond the draft phase, how swiftly wallets and exchanges will adopt new output types, and whether quantum technology progresses beyond the NISQ era.