First quantum-safe Bitcoin tx on mainnet

First quantum-safe Bitcoin transaction hit mainnet yesterday.

Block 964199, mined 26 Aug 2026. Avihu Levy posted the TXID around 22:33 UTC. That’s when it started spreading. StarkWare quote-tweeted it a couple minutes later and put up the blog.

Small test spend. About 44,000 sats out, 5,179 sats fee. No soft fork. No consensus change. Regular Bitcoin rules.

Normal spends use ECDSA. That’s fine today. A big enough quantum computer running Shor’s algorithm would not be fine. The ugly window is the mempool: once you broadcast, the public key is sitting there. In theory a quantum attacker could derive the private key and race you.

QSB tries to close that window. It adds a hash-based lock on top of what Bitcoin already has. The sender grinds off-chain until the transaction hash looks like a valid signature. Bitcoin accepts it. Security then rests on hash preimage resistance, not on “hope nobody copies the key before a miner picks the tx up.” Levy published the method in April. Tomer Giladi helped get it onto mainnet. It builds on earlier Binohash work from Robin Linus.

It only works because the script is non-standard. Regular nodes will not relay it. So it went through MARA Slipstream straight to a miner. Costs a couple hundred dollars in GPU time and a few hours of grinding. Not for daily use.

This does not make Bitcoin quantum-proof. It does not cover Taproot, Lightning, or coins whose public keys are already sitting in the clear. It is a stopgap: a way to move a UTXO behind hashes while the network argues about a real upgrade.

TX: https://mempool.space/tx/305a24ffea912b9cf428f29ebf952321c96dab5bab284fc0d0801562f5abab07

Block: https://mempool.space/block/964199

Levy: https://x.com/avihu28/status/2092742315995480266
Paper + code: https://github.com/avihu28/Quantum-Safe-Bitcoin-Transactions
StarkWare blog: https://starkware.co/blog/the-first-quantum-safe-bitcoin-transaction-has-been-mined/