Quantum-Exposed Bitcoin Supply
Bitcoin held in outputs whose public key is already visible on-chain, so a large quantum computer could in principle derive the private key.
Bitcoin outputs come in two families. Hash-based outputs (P2PKH, P2WPKH, P2SH, P2WSH) publish only a hash of the key until the coins are spent. Key-exposed outputs publish the public key itself: pay-to-public-key (P2PK, the Satoshi-era format), bare multisig (P2MS) and Taproot (P2TR, whose output key is the tweaked public key by design). A quantum computer running Shor's algorithm against secp256k1 would threaten the key-exposed family first, because the key is already there to attack. ByKaranteli measures this supply daily from its own node's UTXO snapshot: total BTC, share of the UTXO set by value and by count, and a dormancy breakdown, with the snapshot hashes published for reproduction. Exposure is a property of the output type, not a statement about when such a machine might exist.