Two Starkware researchers broadcast a quantum resistant Bitcoin transaction on mainnet, in block 964199, using hash based one time signatures built from script opcodes that already exist.

No consensus change. No soft fork. Nobody had to ask Bitcoin Core for anything.

It is about five times the size of a normal transaction, so at fifty sats a byte it stings. At one sat a byte it is nothing. And if the alternative is being quantum vulnerable, that is a price worth paying.

The headline is not the cost. It is that this was possible the whole time.

https://ungovernable.network/shows/bitcoin-brief/the-ai-pocalypse-continues/