A v6 fingerprint is SHA-256 over the key packet with a v6 prefix (64 hex digits) and its key ID is the first 64 bits; a v4 fingerprint is SHA-1 (40 hex digits) with the key ID taken from the last 64 bits (RFC 9580 §5.5.4). v6 signatures include a random salt hashed before the data, which makes chosen-prefix collision attacks on the signed hash impractical. Public-key algorithm IDs 25–28 are X25519, X448, Ed25519 and Ed448; RFC 9980 adds IDs 30–36 for post-quantum algorithms, most of which require v6 keys.
Implementations that support v6 include Sequoia PGP and OpenPGP.js; GnuPG instead writes LibrePGP v5 keys for its newest formats, and keyservers and older tools may reject keys of a version they do not know. Publishing a v6 key alongside a v4 key is the cautious path while the ecosystem catches up.