Bitcoin's quantum debate splits as Adam Back pushes optional upgrades over forced freeze

The quantum computing threat has some of Bitcoin's most vocal developers landing in wildly different places.

Blockstream's CEO, Adam Back, told Paris Blockchain Week attendees on Wednesday that Bitcoin developers should start building optional quantum-resistant upgrades now, even though current quantum computers remain "essentially lab experiments" with progress that has been "incremental" over the 25 years he has tracked the field.

"Preparation is key. Making changes in a controlled way is far safer than reacting in a crisis," the Blockstream CEO said.

He pointed to his company's work testing quantum-resistant transaction signatures on Liquid, a sister network to Bitcoin. He argued that a 2021 Bitcoin upgrade called Taproot was designed flexibly enough to accept new signature methods without disrupting anyone currently using the network.

The comments echo Back's position from last week, when he told CoinDesk that users should have roughly a decade to migrate their keys to quantum-resistant formats.

What is different now is the context around them. BIP-361, the proposal from Jameson Lopp and five other developers published Tuesday, would phase out quantum-vulnerable addresses on a fixed five-year timeline and freeze any coins that fail to migrate.

That includes roughly 1 million bitcoin attributed to Bitcoin's pseudonymous creator, Satoshi Nakamoto, and an estimated 5.6 million coins, Loppsays, have not moved in over a decade.

Back's framing reads as the implicit alternative to BIP-361's forced migration. He did not mention the Lopp proposal directly, but addressed the underlying question of whether Bitcoin's developer community can respond quickly to a sudden quantum breakthrough.

"Bugs have been identified and fixed within hours. When something becomes urgent, it focuses attention and drives consensus," he said, suggesting Bitcoin's rough-consensus governance could handle an emergency without pre-scheduled freezes years in advance.

The two positions represent the core disagreement shaping Bitcoin's quantum debate.

Back is betting that developers can coordinate quickly if the threat accelerates. Lopp is betting they cannot, and that a scheduled freeze is the only way to avoid a disorderly migration under pressure.

Google and Caltech researchers said last month that functional quantum computers capable of breaking Bitcoin's cryptography could arrive sooner than previously estimated, which is what moved the debate from theoretical to active.