Coinbase, custodian of about 5% of bitcoin, says quantum migration can take years

We think the multi-year framing is right for custodians, because Coinbase's conditions split into problems an engineering team can close and one it cannot close alone. The closable ones are properties of a container. P2MR under BIP-360 and P2TRv2 could let post-quantum signature systems be introduced or replaced without a new output format each time ^[5], and Coinbase wants any scheme checked for compatibility with the MPC key-splitting that custodians use ^[15]. That second ask is self-interested, as it should be: 5% of supply is one coin in every 20 ^[21], and Coinbase says it custodies that share ^[1].

The problem that cannot be closed by engineering is the pile of coins that never move. Bitcoin holds old outputs with exposed public keys, reused addresses, dormant holdings and funds whose private keys may already be lost ^[14], and no wallet upgrade reaches an owner who never signs again. Coinbase said that debate should not delay work on post-quantum signature support ^[10]. In our view that puts the two tracks on separate clocks, and the slower one sets how much of the supply the faster one ends up protecting.

There are two ways this plays out differently. The threat may stay hypothetical for longer than the plan assumes: the coverage describes no immediate quantum attack on bitcoin ^[11], and Coinbase's case is that waiting for an announced cryptographically relevant quantum computer would leave too little time to respond ^[3]. Or the post may carry less weight with developers than its length suggests. Decrypt described it as less a mandate than a set of requirements from one of the network's largest stakeholders ^[20], so developers could adopt the container and set the custody asks aside.

The only dollar figure in the coverage is consortium money. Coinbase joined the Bitcoin Security Consortium in July alongside BlackRock and Strategy, with a combined $15 million pledged toward quantum-proofing bitcoin ^[18], after convening its own quantum advisory board in January ^[17]. Neither account includes a migration budget, a timetable or the signature scheme Coinbase would choose.

We would be wrong if BIP-360 or a similar container reaches activation quickly and the MPC and stateless-signing questions close without redesign. The "can take years" estimate would then describe Coinbase's caution.