BIP-361 Targets 6.04M Quantum-Exposed BTC, 30.2% of Circulating Supply
A new Bitcoin proposal would freeze spending from exposed addresses in stages, hitting the 30.2% of supply Glassnode flags as quantum-vulnerable.
A Bitcoin Improvement Proposal designated BIP-361 would progressively lock spending rights out of addresses considered vulnerable to quantum decryption, a mechanism that on current data would eventually touch roughly 6.04 million BTC — 30.2% of circulating supply, according to a May estimate from Glassnode.
The proposal surfaces as quantum computing funding accelerates: the Trump administration committed $2 billion toward the technology’s development in 2026, a figure that has sharpened attention on Bitcoin’s exposure to cryptographic attack well before most analysts expected the risk to become material.
A three-stage freeze mechanism
Per the initiative’s published documentation, BIP-361 would roll out in three phases. The first stage disallows new transfers into addresses flagged as quantum-vulnerable, cutting off further exposure at the point of deposit.
The second stage invalidates ECDSA and Schnorr signature spends outright, a change the proposal ties to “a well-publicized flag-day five years after activation” — giving holders a fixed runway to migrate funds before the rule takes effect. The third and final stage introduces a still-undefined method for recovering legacy unspent transaction outputs (UTXOs) left stranded by the earlier phases.
The mechanism does not discriminate by wallet size or provenance. Satoshi Nakamoto’s dormant holdings — among the largest and oldest UTXO sets on the network — would fall under the same freeze unless migrated to quantum-resistant addresses, a detail that underscores how the proposal treats legacy exposure as a protocol-level risk rather than an individual custody problem.
The data behind the timeline
The urgency traces to a sequence of technical findings over the past several months. Google published research in March 2026 indicating that a sufficiently powerful quantum computer could hijack a Bitcoin transaction within nine minutes in 41% of tested scenarios.
In April, a researcher demonstrated a working attack path by cracking a 15-bit elliptic curve cryptography (ECC) key on a publicly accessible quantum computer, deriving the private key directly from its corresponding public key. The result offered the first practical, if small-scale, evidence that the theoretical threat scales with hardware progress rather than staying confined to whitepapers.
Glassnode’s May figure — 6.04 million BTC, or 30.2% of issued supply, sitting in addresses with publicly visible keys — quantifies the attack surface those two findings point toward. Any address that has ever broadcast a transaction exposes its public key on-chain, making reused or spent addresses the primary target class for BIP-361’s phased restrictions.
What it means for holders and markets
For traders and on-chain analysts, the proposal reframes quantum risk from a distant tail event into a governance and coordination problem with a concrete supply-side number attached. Nearly a third of BTC supply falling under a potential freeze mechanism raises questions about liquidity, custodial migration costs, and how exchanges and cold-storage providers would sequence address rotations ahead of any flag-day.
A successful real-world quantum attack — even a partial one — would carry direct implications for confidence in Bitcoin’s settlement guarantees and, by extension, its price. BIP-361 remains a proposal rather than an activated protocol change, but its existence signals that the developer community is now treating the 30.2%-of-supply exposure figure as an operational, not theoretical, planning input.
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