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Published estimates put about 6 million BTC in outputs whose public keys are already visible on-chain. That is a potential future quantum-attack surface—not evidence that those coins can be stolen with today’s quantum computers. The estimates vary because researchers use different snapshots and counting methods.
The “AI warnings mount” part of the original framing is not substantiated by the cited analyses: they examine quantum computing, and do not identify an AI system or AI-generated finding behind the warnings.
What the “6 million BTC” estimate measures
A public key is not the same thing as a public address. Some Bitcoin output designs reveal a public key on-chain; other outputs can keep it hidden behind a hash until a spend reveals it. Analysts count coins associated with visible keys as quantum-exposed under their chosen definitions. This measures visibility, not whether anyone can currently derive the corresponding private keys.
Two widely cited estimates are similar in scale but are not directly interchangeable. They were published on different dates, use different supply snapshots and classifications, and do not necessarily count the same kinds of exposure.
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| Source and date | Estimate | What the estimate counts or qualifies |
|---|---|---|
| Glassnode Research, May 20, 2026 | 6.04 million BTC, or 30.2% of issued supply | BTC at rest in outputs whose associated public key is already visible, divided into structural and operational exposure. |
| Coinbase Institutional Research, January 6, 2026 | Roughly 6.51 million BTC, or about 32.7% of supply, at block 900,000 | Includes P2PK, bare multisig (P2MS) and Taproot (P2TR), and also discusses address reuse as a source of exposure. |
| Gershteyn and Alber preprint, June 2026 | Roughly 6 million BTC | Its model estimates about 2.3 million BTC as irreducible and 3.7 million as migratable; those categories are model-specific. |
The figures describe different analyses, not a single audited count. In particular, the Glassnode figure is an at-rest estimate, while Coinbase specifies a block-height snapshot and a set of output types. Treating their percentages as if they came from the same date, denominator and classification would obscure those differences.
How public keys become exposed
Structural exposure: visible by output design
Some output types expose a public key in the on-chain output itself. Glassnode classifies early pay-to-public-key (P2PK), bare multisig and Taproot outputs as structural exposure in its at-rest framework. Taproot is not generally unsafe by design; its output key is visible, which is why it falls into this particular measure.
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Operational exposure: revealed through use or custody behavior
Other output types can conceal a public key behind a hash while unused. Reusing a key or address can reveal the key when one output is spent, while other funds associated with that key remain. Glassnode’s May 2026 estimate assigns 1.92 million BTC (9.6% of issued supply) to structural exposure and 4.12 million BTC (20.6%) to operational exposure. Those are Glassnode’s classifications and supply figures, not universal categories applied identically by every estimate.
What a quantum attacker would have to do
The concern is a signature attack: a sufficiently capable quantum computer could, in principle, use a visible public key to derive its private key and then forge a valid spend. Coinbase distinguishes a long-range attack against a key already exposed on-chain from a short-range attack against a key revealed when a transaction is broadcast. The latter creates a race around a spend; the former concerns funds associated with keys already visible.
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That theoretical attack path is not the same as a present-day capability. Coinbase says current quantum machines remain far below what would be needed to compromise Bitcoin’s cryptography. Glassnode likewise cautions that its supply estimate is not a forecast of when practical attacks become possible or an estimate of exploit probability. The estimate does not mean the counted BTC are currently hackable, imminently at risk, or certain to be stolen.
A June 2026 preprint by Iosif M. Gershteyn and Jacob A. Alber models probabilities for a cryptographically relevant quantum computer by 2035, 2040 and 2050. Those are the authors’ forecasts, not observed capabilities or consensus dates. The cited analyses concern signature security and migration, not an attack on Bitcoin mining.
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What holders and Bitcoin developers can do
Reduce avoidable operational exposure
Glassnode describes address hygiene, reducing key reuse, reserve management and migration planning as ways to reduce operational exposure. Coinbase similarly recommends avoiding reuse and moving vulnerable UTXOs to unique destinations. These practices can limit future exposure from reuse; they cannot make a public key already recorded on-chain secret again.
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Changing where funds are held and changing Bitcoin’s signature rules are different tasks. A wallet or hardware device cannot reverse on-chain disclosure by itself. Longer-term protection would require a migration path to post-quantum signatures, along with protocol and ecosystem changes that let users move funds under the new rules.
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Glassnode and Coinbase discuss BIP-360/P2MR as a proposed mitigation direction, not proof that Bitcoin has already upgraded. A proposal, a migration plan and a deployed protocol change are distinct stages; current proposal status and implementation details should be checked against current Bitcoin development sources before relying on them.
Does the “AI warning” claim hold up?
Not on the evidence cited here. Glassnode, Coinbase and the June 2026 preprint address quantum computing and Bitcoin-key exposure. They do not establish that AI produced the findings, name a particular AI system, or verify a separate AI warning. The more precise description is that quantum-risk analysis has estimated a sizable pool of BTC with already-visible public keys.
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