Base Cobalt upgrade adds optional seizure rule for B20

Base will deploy the Cobalt upgrade to mainnet during scheduled maintenance on Sept. 30 from 18:00 to 20:00 UTC. The upgrade introduces an optional administrative operation, seizeWithMemo, for B20 tokens that can reassign a holder’s balance to another address while preserving total supply.

The seizeWithMemo operation moves a specified amount from one account to another without burning tokens. It bypasses ordinary transfer policies and allowance checks, and it keeps the token’s total supply unchanged by sending the assets to a recipient rather than destroying them.

Issuers must configure several items before a seizure can be executed. An account must be granted SEIZE_ROLE, the issuer must set SEIZE_EXEMPT_POLICY to identify which accounts can be targeted, the seizure function must not be paused, and the holder must have a sufficient balance. If SEIZE_EXEMPT_POLICY is not set, accounts are exempt by default.

A separate recipient policy controls where seized tokens may be sent. If the recipient policy is left unset, any otherwise valid destination is permitted. Ordinary transfer permissions and approvals remain distinct from seizure controls; approval of a spender does not remove seizure eligibility checks.

Cobalt also marks the existing burnBlocked function as deprecated while keeping it callable. burnBlocked destroys tokens held by accounts denied by the transfer sender policy. Issuers therefore have two administrative options: reassign a balance via seizure, which preserves supply, or burn tokens, which reduces supply. Seizure and burn actions use separate roles and have separate pause controls.

The upgrade has been active on Sepolia since Sept. 23. Node operators must upgrade clients to v1.4.2 to support Cobalt on mainnet by the Sept. 30 maintenance window. Seizure features remain disabled until an issuer explicitly configures eligibility and assigns the required roles.

B20 is Base’s native ERC-20–compatible token standard, available in Asset and Stablecoin variants. The standard already includes role and policy mechanisms for transfer and administrative actions; Cobalt adds a new administrative tool while leaving configuration and permissioning to token issuers and developers.