Blockstream's CEO told Paris Blockchain Week that Bitcoin should build quantum-resistant upgrades now through voluntary migration, opposing BIP-361's plan to freeze coins in vulnerable address formats on a five-year timeline.
Adam Back, the Blockstream CEO and inventor of Hashcash — the proof-of-work system that underpins Bitcoin's mining — told Paris Blockchain Week on Wednesday that Bitcoin should begin building quantum-resistant transaction signatures now, while firmly opposing a rival developer proposal that would freeze coins held in vulnerable address formats on a fixed timeline.
The disagreement centres on BIP-361, a proposal published Tuesday by Jameson Lopp and five co-authors titled "Post-Quantum Migration and Legacy Signature Sunset." It lays out a phased schedule: three years after activation, new payments to legacy address types that expose public keys on-chain would be banned, though existing holders could still spend; at the five-year mark, ECDSA and Schnorr signature schemes would be invalidated entirely, freezing any coins that haven't migrated to quantum-resistant addresses. Unmigrated funds — including an estimated 1.7 million BTC held in pay-to-public-key formats, roughly 34 per cent of the total supply — would become permanently unspendable.
That 1.7 million figure includes the early Bitcoin holdings widely attributed to Satoshi Nakamoto, worth between $70 billion and $80 billion at current prices. A freeze would therefore accomplish something the Bitcoin community has debated for over a decade: rendering the founder's coins permanently inaccessible. BIP-361's authors frame this as an inevitable consequence of security hardening rather than a deliberate policy choice, but the political implications are difficult to ignore.
Back's position is that optional, incremental upgrades are safer than a protocol-mandated deadline. "Making changes in a controlled way is far safer than reacting in a crisis," he told the conference, pointing to Blockstream's work testing quantum-resistant transaction signatures on Liquid, a Bitcoin sidechain the company operates. He described current quantum computers as "essentially lab experiments" while emphasising that he has followed the field for more than 25 years and considers the progress incremental rather than exponential. His preferred approach would let users migrate voluntarily to quantum-safe address types — building on Blockstream's earlier technical work — without the coercive mechanism of a coin freeze.
Lopp and his co-authors are betting that voluntary migration won't happen fast enough. Their proposal builds on BIP-360, an earlier soft-fork framework, and gives the network a full five years to transition — a generous timeline by software standards, but potentially inadequate for an ecosystem where millions of coins sit in wallets whose owners may be dead, have lost their keys, or simply aren't paying attention. The freeze is the backstop: a guarantee that quantum-vulnerable coins cannot be spent by an attacker even if their owners never move them.
The debate was triggered by a paper published last month by researchers at Google and Caltech suggesting that functional quantum computers capable of breaking Bitcoin's elliptic-curve cryptography could arrive sooner than the field's previous consensus estimates. Neither Back nor Lopp disputes that the threat is real; they disagree on how much time remains and, more fundamentally, on whether Bitcoin's governance model can execute a coordinated migration without a hard deadline. Back has long argued that Bitcoin's decentralised development process is more resilient than it appears, pointing to historical incidents where critical bugs were patched "within hours." Lopp's camp views that optimism as reckless when the stakes involve a third of all bitcoin in circulation.
No consensus is imminent. BIP-361 faces the same slow, contentious review process that every significant Bitcoin protocol change endures; the last comparable debate — over the Taproot upgrade — took roughly two years from proposal to activation. The quantum timeline, whatever it turns out to be, will not wait for Bitcoin's governance to reach unanimity. That asymmetry is the core of Lopp's argument, and it is the reason the proposal exists at all: not because a quantum computer can break Bitcoin today, but because by the time one can, it may already be too late to act. Back would counter that freezing $70 billion in coins is not a decision any decentralised network should make on a fixed schedule — and that the cure, imposed prematurely, could prove more damaging than the disease.
