Is Bitcoin Quantum-Safe Now? One Transaction Says Partly

StarkWare said Wednesday that a quantum-safe Bitcoin (BTC) transaction has been mined on the live network, a first for the method.

On-chain data shows the transaction spent a 10,000-satoshi output, worth about $8 at current prices, and paid a fee of 5,179 satoshis.

Follow us on X to get the latest news as it happens

Quantum-safe Bitcoin, mined on mainnet, Today.Designed by @avihu28 – the first ever quantum-safe Bitcoin transaction was built in collaboration with @MARAFoundation_ and our own @giladi_tom85141.Every chain faces the same quantum deadline. Today we took a huge step to move…

— StarkWare 🥷 (@StarkWareLtd) August 26, 2026

How the Quantum-Safe Bitcoin Transaction Works

Quantum-Safe Bitcoin (QSB) attaches a hash-based lock beside the elliptic curve signature that normally guards a Bitcoin output. Shor’s algorithm, the quantum technique that derives private keys from published public keys, cannot break hash functions.

StarkWare researcher Avihu Levy published the QSB method in April. It uses signature grinding. This produces a valid Bitcoin signature without a private key. 

The sender grinds offchain until a candidate spending transaction hashes to a value that is itself a validly formatted signature.

Security then rests on reversing a hash rather than keeping a private key secret. The technique builds on Binohash, developed by Robin Linus, the creator of BitVM.

MARA Pool mined the transaction in block 964,199. What worked was a single construction, not an upgrade, and Bitcoin itself remains unchanged.

What the QSB Method Cannot Do

StarkWare said the method does not make Bitcoin quantum-safe. Three constraints narrow what the spend actually protects.

The first limit is prior exposure. An address whose public key already sits on-chain gains nothing, because an adversary with a quantum computer could derive the corresponding private key.

The second is the migration step. Coins reach a hash-secured output through a transaction signed the ordinary way, which exposes the sending address’s public key. The output spent on Wednesday was funded in July by exactly such a transaction.

The third is delivery. QSB transactions use nonstandard formats, so ordinary nodes will not relay them, and MARA’s Slipstream service supplied the route to a miner.

Cost compounds the limits. Levy’s repository puts the offchain compute at $75 to $150, while StarkWare described this transaction as costing several hundred dollars. 

“People have long assumed that protecting Bitcoin holdings from a quantum adversary would require changing the Bitcoin protocol. Today shows otherwise. A soft fork is still the better long-term answer, as StarkWare has argued for consistently, but it is no longer the only option,” the blog read.

Bitcoin has not adopted a protocol-level fix, and Wednesday’s transaction does not change that.

Subscribe to our YouTube channel to watch leaders and journalists provide expert insights