Quantum solvency · Wrapped-asset custodian

cbBTC custody reserve

Coinbase (Coinbase Wrapped BTC custodian)

Scored from cbBTC proof of reserves, coinbase.com (2026-09-28), 44 of 44 published addresses read. The bitcoin Coinbase holds to back cbBTC on Base, Ethereum, Solana and Arbitrum, as listed on Coinbase’s own proof-of-reserves page (total reserve 95,782.86 BTC at capture). The page is rendered for browsers only, so the address list is captured from it rather than fetched from an API; re-capture before each snapshot. Snapshot .

By exposure class

Practical risk

An attacker must recover each key separately. 13 exposed keys hold 10 BTC or more, 36,491 BTC in total; that is the part worth attacking first, and the part to sweep to fresh keys first.

Largest exposed keys

Disclosure freshness

Published this month. Read from a publication dated 2026-09-28, 21 days ago. Read from a page that only a browser can render; re-captured before each snapshot.

Custody, as observed on-chain

Of the 85,742 BTC in the 38 addresses read, 39% is spent by a single key (indistinguishable from MPC on-chain), 0% through a multisig script, and 61% has never spent, so its control is not yet visible.

Read from 38 of 44 published addresses, holding 85,742 BTC, on 2026-09-30.

Repeated nonces

418 signatures from 20 keys across 20 addresses were checked and no nonce was repeated. For 4 busy addresses only the most recent transactions were read.

What it would take to move the exposed balance

189 unspent outputs in 1 transaction, about 0.0002 BTC in fees at the one-hour rate (about $16 at today’s price), using well under one percent of a day’s block space.

Each of the 189 unspent outputs is spent once into one fresh output of the same script family, in transactions of up to 400 inputs. Fee rates are mempool.space's recommendations at 2026-09-30T22:04:40.474Z. Signing ceremonies, custody procedures and withdrawal queues are not included and usually dominate.

Live badge for this reserve. It reads the latest snapshot and links back here.

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