ARK Invest has put a sharper spotlight on one of Bitcoin’s longest-running technical concerns: the possibility that future quantum computers could break the cryptography protecting older wallets and exposed public keys. In a recent white paper, the investment firm said the threat is not immediate, but it is serious enough to deserve planning now. The report arrives as the broader crypto industry, researchers, and large asset managers increasingly discuss how much of Bitcoin’s supply could be vulnerable if quantum computing advances faster than expected.
Why ARK Invest sees one-third of Bitcoin supply at risk from quantum threat
The core of the issue is Bitcoin’s reliance on elliptic curve cryptography for digital signatures. In normal conditions, that system is secure. But a sufficiently powerful quantum computer running Shor’s algorithm could, in theory, derive a private key from a public key, allowing an attacker to spend coins they do not own. That risk applies most directly to coins in address types where the public key is already exposed, including early pay-to-public-key outputs and addresses that have been reused after spending.
ARK Invest’s white paper, authored with contributors from Unchained, argues that quantum risk should not be treated as a single dramatic event but as a gradual technological progression with warning signs along the way. That framing matters because it shifts the debate from speculation to preparedness. According to ARK Invest and Unchained researchers, the relevant question is not whether Bitcoin is broken today, but how the network and its users should respond before quantum machines become cryptographically relevant.
The “one-third” figure has become a focal point in the discussion because several recent analyses place the amount of potentially exposed Bitcoin in the range of roughly one-quarter to one-third of circulating supply. A recent Swiss Bitcoin Institute paper estimated that assets representing nearly a third of Bitcoin’s total supply could become vulnerable under a sufficiently advanced quantum attack. Forbes also reported that expert discussions and analysis tied to the Presidio Bitcoin Quantum Summit put the figure at about 31% of circulating supply by value.
What makes some Bitcoin more vulnerable than others
Not all bitcoin faces the same level of risk. Coins stored in modern address formats that have never revealed their public keys are generally considered less exposed. By contrast, older coins are a bigger concern because their public keys are already visible on the blockchain. Once a public key is exposed, a future quantum attacker would have the information needed to attempt private-key recovery.
This creates a split within Bitcoin’s supply:
- Lower-risk coins: funds in newer address formats that have not exposed public keys.
- Higher-risk coins: early pay-to-public-key outputs and reused addresses.
- Special concern: dormant legacy holdings, including coins that may be inaccessible because their owners are unknown or keys are lost.
One reason the issue has drawn so much attention is the large number of early coins that cannot easily be migrated. Forbes noted that roughly 1 million BTC in early pay-to-public-key addresses, often associated with Bitcoin’s pseudonymous creator, cannot be moved to quantum-safe formats unless the private keys are available. If those keys are lost, the network may eventually face a difficult policy question over whether such coins should remain spendable under a post-quantum regime.
Industry warnings are becoming more visible
ARK Invest is not alone in flagging the issue. BlackRock, in risk disclosures for its iShares Bitcoin Trust, has warned that advances in mathematics and technology, including quantum computing, could undermine the cryptography supporting Bitcoin. That language does not suggest an imminent break, but it shows that large financial institutions now consider quantum risk material enough to include in formal investor documents.
Other market participants have gone further. Coverage of comments from Coinbase’s head of institutional research said as much as one-third of Bitcoin’s total supply could be vulnerable to quantum computing under certain future conditions. Meanwhile, some strategists have cited quantum concerns as part of a broader reassessment of Bitcoin’s long-term security assumptions.
According to David Puell, ARK Invest’s research trading analyst and associate portfolio manager for digital assets, the point of the white paper is to map the stages of risk rather than to predict a sudden collapse. The paper’s co-authors from Unchained make a similar case: Bitcoin still has time to prepare, but only if the ecosystem treats migration planning as a technical priority now.
How Bitcoin could respond
The most widely discussed solution is a gradual migration to post-quantum cryptography. That would likely require a Bitcoin Improvement Proposal, broad community consensus, wallet support, exchange coordination, and a long transition period. Recent reporting indicates that Bitcoin developers have already begun taking early steps, including work tied to BIP 360, which aims to reduce public-key exposure in future transaction design.
Researchers also note that a full transition would be operationally difficult. An academic paper on Bitcoin quantum safety argues that upgrading the network’s public-key cryptography is the only known way to prevent this class of attack once cryptographically relevant quantum computers arrive. Another study estimates that migration could require substantial time and careful capacity management, especially if the network must process large-scale wallet movements under stress.
For investors and custodians, the practical steps are more immediate:
- Avoid address reuse.
- Move funds to wallet types that minimize public-key exposure.
- Monitor protocol-level proposals for post-quantum upgrades.
- Review custody providers’ quantum-readiness plans.
Why the debate matters now
The quantum threat to Bitcoin remains a future-facing risk, not a present-day exploit. No public evidence shows that existing quantum computers can break Bitcoin’s cryptography today. Still, the discussion matters because Bitcoin is increasingly held by institutions, exchange-traded products, and long-term investors who need to think in decades, not quarters.
There is also a broader policy dimension. The same quantum advances that could threaten Bitcoin would also challenge widely used public-key systems across finance, government, and the internet. In that sense, Bitcoin is not an isolated case but part of a much larger cybersecurity transition already under way as organizations prepare for post-quantum standards.
A balanced view is important. Skeptics of the near-term threat argue that useful quantum attacks remain years away and that Bitcoin has historically adapted to technical challenges over time. More cautious analysts counter that the scale of exposed legacy coins and the difficulty of coordinating a global protocol change mean preparation cannot wait until the last minute. The evidence available today supports one clear conclusion: ARK Invest sees one-third of Bitcoin supply at risk from quantum threat not as a prediction of imminent failure, but as a warning that the network’s long-term resilience will depend on early action.
Conclusion
ARK Invest’s warning adds institutional weight to a debate that has moved from theory toward practical planning. The firm’s analysis suggests that a meaningful share of Bitcoin’s supply could face quantum-related exposure if powerful enough machines emerge and the network has not upgraded in time. For now, Bitcoin remains secure under current real-world conditions. But as quantum research advances and more institutions hold digital assets, the pressure to build a credible migration path is likely to grow.
Frequently Asked Questions
What does ARK Invest mean by quantum risk to Bitcoin?
It refers to the possibility that future quantum computers could break the cryptographic signature systems used by Bitcoin, especially where public keys are already exposed on-chain.
Is one-third of Bitcoin actually vulnerable today?
Not in the sense of being attackable with current public quantum technology. The estimate refers to the portion of supply that could become vulnerable if cryptographically relevant quantum computers are developed.
Which bitcoin is most at risk?
Older coins in pay-to-public-key outputs and funds in reused addresses are generally seen as more exposed because their public keys are already visible.
Has BlackRock also warned about this issue?
Yes. BlackRock’s iShares Bitcoin Trust prospectus includes risk language stating that advances in computing, including quantum computing, could undermine Bitcoin’s cryptography.
Can Bitcoin be upgraded to resist quantum attacks?
Potentially, yes. Researchers and developers are discussing post-quantum migration paths, but any major change would require technical development, broad consensus, and time.
Is this only a Bitcoin problem?
No. Quantum computing threatens many public-key cryptography systems used across digital infrastructure, not just cryptocurrencies.
