Glassnode on May 20, 2026 classified 1.92 million BTC - 9.6% of Bitcoin's total supply - as structurally exposed to a future quantum computing breakthrough, with another 4.12 million BTC at operational risk from address reuse and exchange custody practices. The report maps 30.2% of issued supply as exposed, the most detailed such accounting published to date.

Quantum risk in Bitcoin's supply is now mapped in detail. Get the context behind Glassnode reports and on-chain data like this every weekday - free, at Web Snack.

How Accelerating Quantum Hardware Brought Bitcoin's Address Types Into Focus

The quantum threat to Bitcoin's elliptic curve cryptography accelerated through early 2026 as hardware access costs fell. In April, an independent researcher cracked a 15-bit elliptic curve key on cloud-rentable hardware in about 45 minutes, winning 1 BTC from Project Eleven's Q-Day Prize - a record that stood at 6 bits just seven months earlier. A March 2026 white paper from Ark Invest estimated breaking Bitcoin's 256-bit ECC would require approximately 2,330 logical qubits and tens of millions to billions of quantum gates.

No quantum computer today is close to that threshold. But cryptographic transitions take years, and coins already exposed cannot be un-exposed retroactively.

1.92M BTC in Exposed Outputs: What the Glassnode Numbers Show

Glassnode separates the exposed supply into two distinct categories. Structural exposure covers 1.92 million BTC - outputs whose script design reveals the public key on-chain by default, regardless of how carefully owners manage their wallets. The three address types in this category are Satoshi-era Pay-to-Public-Key (P2PK) outputs, legacy bare multisig structures, and modern Pay-to-Taproot (P2TR) addresses. Satoshi Nakamoto's estimated 1.1 million BTC sits here, alongside another 620,000 BTC in other early Satoshi-era coins.

The larger operational exposure bucket totals 4.12 million BTC, or 20.6% of supply. These are coins initially protected by hash layers but made visible through address reuse, partial spending, or custody practices. Exchanges account for 1.63-1.66 million BTC of this total - roughly 40% of the entire operationally exposed pool. Binance shows 85% of its labeled holdings in exposed outputs; Bitfinex sits near 100%. Coinbase holds just 5% in exposed structures. US, UK, and El Salvador sovereign wallets show zero exposure under Glassnode's methodology.

Why the Exchange Gap Is the Most Actionable Part of This Data

The structural 1.92 million BTC cannot be fixed retroactively. Those coins' public keys are already on-chain. But Glassnode identified the larger operational category as correctable without any protocol change. The firm noted exchange-held BTC has drifted from about 55% operationally safe in 2018 to roughly 45% today - a trend it called "straightforwardly reversible through standard address-management practices" such as address rotation and avoiding key reuse. That portion of the risk can shrink through decisions exchanges can make now.

The disparity between custodians is immediate: Binance's 85% exposure rate against Coinbase's 5% reflects wallet hygiene choices already made, not future threats.

BIP-360 and the Migration Path Exchanges Have Not Yet Taken

Bitcoin Improvement Proposal 360 proposes a new Pay-to-Merkle-Root (P2MR) output type as a voluntary migration path to quantum-resistant addresses. P2MR removes Taproot's quantum-vulnerable key path spend but does not itself add post-quantum digital signatures. The report cited a March 2026 Google Quantum AI paper alongside BIP-360 as the primary technical references for the migration framework.

Glassnode advised exchanges and custodians to reduce key reuse, improve address hygiene, and plan migration ahead of any quantum breakthrough. The firm explicitly does not take a position on whether, or when, practical quantum attacks against Bitcoin will become possible.

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P.S. This article is for informational purposes only and does not constitute investment advice. Always conduct your own research and make independent decisions.