Coinbase, which custodies approximately 5% of existing Bitcoin, has released its technical considerations for Bitcoin's transition to post-quantum security, warning that the migration could take several years and urging early preparation from all parties. The company recommends exploring flexible output designs such as BIP-360 (P2MR) and P2TRv2, and adopting a phased transition approach to support both classic and post-quantum signature mechanisms. Coinbase also emphasized that issues such as dormant funds, lost private keys, and unmigrated wallets should be addressed separately to avoid delaying the broader post-quantum security upgrade.