Base will ship its Cobalt upgrade to mainnet on September 30 at 18:00 UTC, according to the network's upgrade overview and status page. The release introduces seizeWithMemo, an administrative operation that lets issuers of B20 tokens move a specified amount from a holder to another address — a capability the chain's native token standard did not previously offer as a standalone function.
Maintenance is scheduled from 18:00 to 20:00 UTC, and the v1.4.2 release notes instruct node operators to upgrade by 18:00 UTC on September 30. Sepolia has been running the upgrade since September 23.
What seizeWithMemo actually does
B20 is Base's ERC-20-compatible token standard, issued in Asset and Stablecoin variants. The new operation preserves total supply and moves tokens directly from one address to another, skipping ordinary transfer policies and holder allowances. In practice, that means an issuer can relocate tokens without the holder's signature and without the usual policy checks that govern a normal transfer.
Seizure is off by default for every B20 token. To execute one, an issuer needs four things in place: the SEIZE_ROLE, an unpaused seizure function, a permitted recipient, and sufficient balance in the holder's account.
The exemption layer is where most of the configuration work sits. SEIZE_EXEMPT_POLICY exempts everyone from seizure when it's left unset, so an issuer has to explicitly configure which accounts lose that exemption before any tokens can be taken from them. A separate recipient policy controls where seized tokens can land; leaving it unset allows any otherwise valid destination.
Seizure and burning stay on separate tracks
Cobalt doesn't replace B20's existing enforcement tool. The standard already includes burnBlocked, which lets an authorized caller destroy tokens held by an account that the transfer sender policy has denied. Cobalt marks burnBlocked as deprecated but keeps it callable with its existing behavior intact.
The two mechanisms don't share controls. Seizure and burning run on separate administrative roles and separate pause switches, so an issuer can halt one without touching the other. That separation matters for teams that want to keep a seizure capability dormant while still using blocked-account burning, or the reverse.
The upgrade path for node operators
The v1.4.2 release adds Cobalt mainnet support, and the instruction to operators is direct: upgrade by September 30 at 18:00 UTC. Base's status page lists the mainnet upgrade as scheduled, with the two-hour maintenance window beginning at the same time.
Sepolia's September 23 activation gives operators and B20 issuers a test environment that's already running the new code, which is where exemption and recipient policies can be tried before mainnet. The upgrade overview lists mainnet as shipping on September 30.
What issuers need to decide before activation
Every B20 token starts with seizure disabled, and the default exemption policy keeps all holders out of reach. Issuers who want the capability have to configure both the exemption list and, if they care about destinations, the recipient policy. Those who leave the settings alone keep the status quo: transfers, allowances, and burnBlocked as before.
Base hasn't published a list of issuers planning to enable seizure, and the upgrade documentation doesn't say whether any have configured it on Sepolia ahead of the mainnet date. The remaining question for token teams is whether to turn the function on at all — and if so, which accounts to exempt first.
