Base Details B20 Seize Functionality and Composite Policies for Cobalt Hardfork

Documentation released on Sept. 30 details two major updates coming to the Base network's B20 token specification during the upcoming Cobalt hardfork ¹². The network is introducing a dedicated administrative seizeWithMemo function alongside composite policy logic in the PolicyRegistry, altering how token issuers handle blocked balances and compliance rules on-chain ¹².

At the Cobalt activation, the B20 standard—which governs both standard B20 assets and stablecoins—will gain a native administrative balance transfer mechanism ¹. This operation shifts administrative balance removal from the legacy burnBlocked function to seizeWithMemo, allowing an authorized administrator to reassign balances directly to a treasury or specified address without modifying total supply ¹. The function is restricted by a new SEIZE_ROLE, an independent pause vector, and two policy slots: SEIZE_EXEMPT_POLICY and SEIZE_RECEIVER_POLICY ¹. The legacy burnBlocked method remains callable and unchanged for backward compatibility, though issuers seeking to destroy seized balances must now seize tokens to an intermediate address and subsequently execute a standard burn ¹. Base noted that the feature is opt-in per token: unconfigured seize policy slots default to an always-allow state, causing unauthorized seize attempts to revert ¹.

Composite Rules in PolicyRegistry

Alongside the balance transfer updates, Base is expanding its PolicyRegistry with composite policies using UNION and INTERSECT gates ². Previously, combining multiple permissions—such as an internal know-your-customer list and a broader sanctions list—required issuers to manually sync flattened lists using off-chain infrastructure ².

Under the Cobalt specification, issuers can combine between two and four simple allowlists or blocklists into a single composite policy without copying membership entries ². Checks are evaluated dynamically against the live state of referenced child policies and short-circuit to optimize execution gas ². The changes to the registry are strictly additive, maintaining compatibility with existing simple policies deployed during the current Beryl era ². At the time of writing, broader markets traded flat to slightly lower on the day, with $ETH hovering at $2,673 and total crypto market capitalization at $2.84T. Base confirmed that Cobalt has not yet activated, leaving the new selectors currently undialable on-chain ¹.