COINBASE SAYS IT HOLDS 5% OF ALL BITCOIN — IT WANTS QUANTUM-SAFE SIGNATURES THAT SUIT ITS MPC CUSTODY — A FREEZE IS ON ITS LIST OF OPTIONS FOR OLD COINS

Coinbase published “Working Together on Bitcoin's Post-Quantum Readiness” on October 13, 2026, under the name of Shashank Agrawal. It says Coinbase “holds ~5% of all BTC in existence” and that bitcoin should start preparing now, because “the migration will be a challenging, complex, and multi-year process.” It points to a flexible output type such as P2MR (BIP-360) or P2TRv2, and to a 1-of-2 setup where the same coins can be spent with either a classical key or a post-quantum key.

Further down is the part about Coinbase's own keys. “For Coinbase and many of our customers, MPC-friendliness is an important consideration in the choice of PQ schemes.” MPC splits control of one key across machines the custodian runs. The post adds: “Some schemes, including certain lattice-based approaches, may be more amenable to MPC than others.” Coinbase says this is a factor in picking a scheme, not a request for anyone to build an MPC protocol.

On old coins, the post lists “Legacy-signature sunset, freeze, rate-limiting, or rescue alternatives” as options to weigh, and names “Satoshi-era or otherwise highly concentrated holdings” and “Lost keys or inaccessible seeds” among the cases. It backs none of them, and calls itself “an input to an open discussion, not a set of instructions or a final Coinbase position.”

Coinbase customers won't pick their signature. Coinbase will. Someone who holds their own key decides when to move to a new output type, and can move before any freeze is on the table. A custodian holding 5% of all coins is a reason to read this post closely. It is not a reason for that custodian's vault to set the terms. At the time of this writing, bitcoin was $81,910.