Bitcoin Developers Propose BIP-361: Quantum-Proof Migration That Would Freeze Millions of Legacy Coins
In a move that could reshape the security of Bitcoin’s unspent transaction outputs forever, Bitcoin developers have introduced BIP-361 — officially titled “Post Quantum Migration and Legacy Signature Sunset.” The draft was published in the official Bitcoin repository on April 14, 2026, and pinned the following day by editor murchandamus.
The proposal addresses a long-discussed but increasingly urgent threat: quantum computers capable of breaking today’s elliptic-curve cryptography. According to on-chain data cited in the BIP, as of March 1, 2026, more than 34 % of all bitcoins — roughly 6.5–6.9 million BTC — have their public keys exposed on the blockchain. This includes approximately 1.7 million BTC sitting in ancient Pay-to-Public-Key (P2PK) addresses, some of which are widely believed to belong to Satoshi Nakamoto and are currently valued at around $74 billion.
Three-Phase Sunset Plan
BIP-361 outlines a structured, multi-year migration to post-quantum security.
- Phase A (3 years after activation)
The network will stop accepting new deposits to legacy vulnerable address types. Owners will still be able to spend from these addresses, but no one will be able to send fresh BTC to them.
- Phase B (5 years after activation)
ECDSA and Schnorr signatures on legacy outputs become completely invalid. Any attempt to spend from these quantum-vulnerable UTXOs will be rejected by the network, effectively freezing the coins in place.
- Phase C (rescue mechanism, still under development)
A zero-knowledge proof system tied to BIP-39 seed phrases would allow legitimate owners to prove ownership of frozen coins and reclaim them under a post-quantum address.
The proposal builds directly on BIP-360, introduced in February 2026. That earlier BIP introduced a soft fork creating a new output type called pay-to-Merkle-root (P2MR) — essentially a Taproot-style construction without the quantum-vulnerable “key path.” While BIP-360 protects all newly created coins, it leaves the existing 34 % of supply exposed. BIP-361 is the mechanism designed to handle that legacy risk.
The Economic and Philosophical Argument
The authors lean heavily on Satoshi Nakamoto’s own words. In the original Bitcoin whitepaper era, Satoshi noted that lost coins simply make the remaining supply more valuable — “think of it as a donation to everyone.” The BIP-361 authors flip the logic for the quantum era:
> “Coins stolen by a quantum computer would devalue every other bitcoin — think of it as theft from everyone.”
They frame the temporary freeze not as confiscation, but as a protective measure to prevent a catastrophic wealth transfer that would undermine confidence in the entire monetary system.
Why Now? External Pressure Is Mounting
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Sharp Backlash from the Bitcoin Community
- Brian Trollz, editor at Bitcoin Magazine, outright rejected the proposal.
- Marty Bent, founder of TFTC, called the idea “ridiculous.”
- Phil Geiger of Metaplanet quipped: “We have to steal people’s money so their money isn’t stolen.”
- Frederic Fosco, co-founder of OP_NET, was blunt: “It’s confiscation, period. This rewrites ‘not your keys, not your coins’ into ‘your keys, but we froze your coins anyway.’”
Critics argue that the proposal violates Bitcoin’s core principle of self-custody and sets a dangerous precedent for protocol-level intervention in user funds.
As of April 17, 2026, BIP-361 remains a draft with no activation parameters or signaling mechanism defined. Whether the Bitcoin community will ultimately accept a hard deadline on legacy signatures — or reject the plan as an overreach — will likely dominate discussions at upcoming developer conferences and on the bitcoin-dev mailing list in the coming weeks.