QRL mainnet launches with XMSS as the mandatory signature scheme for every account. source
1 Signature scheme 10/10, weighted 30%
Band 10: A post-quantum signature is the mandatory scheme for all accounts on mainnet.
XMSS is the mandatory signature scheme for all accounts on the QRL mainnet that launched in June 2018. There is no elliptic-curve alternative on the network, so no account can opt back into a quantum-vulnerable scheme. source