Casa security chief Jameson Lopp says a quantum computer able to break Bitcoin (BTC) is orders of magnitude away. Yet the same skeptic warns that preparations for Bitcoin’s Q-Day are already running late.
That tension puts about 2.6 million BTC, worth roughly $207 billion, at the center of the debate. Those coins sit in addresses that may never move to quantum-safe cryptography.
How Far Away Is Bitcoin’s Q-Day, Really?
Casa provides multi-key Bitcoin custody. In a recent interview, Lopp argued that closing the gap would take several massive breakthroughs.
The hardware supports his view. Google’s Willow chip runs on 105 qubits. In March, Google estimated that cracking Bitcoin’s signatures would need fewer than 500,000.
That is a gap of more than 4,700-fold. However, Lopp added a caveat. Breakthroughs in artificial intelligence (AI) tend to spill into other industries, and quantum research could be next.
The risk also targets Bitcoin’s elliptic-curve signatures, not the SHA-256 hashing behind mining. Quantum speedups for mining are far weaker.
What If Bitcoin Has Less Than a Decade?
Stefano Gogioso, an Oxford quantum computing lecturer and member of BeInCrypto’s Future Tech & AI Council, sees a tighter window. He co-founded Spooqy, a startup building quantum money.
Gogioso defines Q-Day as the point when Bitcoin’s secp256k1 curve can be broken within one block, roughly 10 minutes. His team’s models place it in the early-to-mid 2030s.
Indeed, that's Bitcoin's Q-Day: when we can break secp256k1 in under a block's time.
— Stefano Gogioso (@StefanoGogioso) October 24, 2026
Our forecasting models set it to the early/mid 2030s based on current technology trends, depending on how conservative we want to be in our estimates.
At a July Q-Day expert panel, he argued that even a small chance of a break justifies preparing now.
Why Is Governance the Real Bottleneck?
Lopp frames the deadline himself.
“I’m still hopeful that we have at least a decade or more, because if we have less than a decade, we’re behind… as we all know, Bitcoin is very, very difficult to change.”
Jameson Lopp, chief security officer at Casa, said in a recent interview.
His September essay explains why. Lopp co-authored BIP-361, a draft proposal to phase out quantum-vulnerable signatures over several years.
He does not expect serious calls to activate it unless a capable quantum computer looks under 10 years away. Gogioso’s forecast falls inside that window.
Migration itself is slow. Bitcoin research firm Chaincode Labs estimates a full upgrade could take five to 15 years, according to Lopp’s essay.
In July, Gogioso blamed Bitcoin’s lack of formal governance for the slow response.
Which Coins Would Fall First?
Not every Bitcoin faces the same risk. Coins with public keys already on-chain give an attacker unlimited time.
These include early pay-to-public-key (P2PK) outputs, reused addresses, and Taproot outputs. Lopp estimates about 2.6 million BTC, or roughly 13% of supply, could never migrate.
“Bitcoin’s quantum problem is not urgent in the sense that users should panic today. It is urgent in the sense that decentralized systems must solve hard coordination problems before they become emergencies.”
Lopp wrote.
Large holders have started moving. Coinbase, which holds about 12% of all BTC, published a post-quantum readiness plan in October. Bitcoin’s protocol, however, still has no agreed deadline.
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