> ## Documentation Index
> Fetch the complete documentation index at: https://base-a060aa97-feat-add-changelog.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# B20

> B20 changes introduced by the Cobalt upgrade.

Cobalt is additive-only. It does not change or remove any Beryl selector, event topic, or error
selector. Symbols that supersede Beryl symbols are deprecated rather than deleted, so existing
integrations remain callable.

<Warning>
  Cobalt has not activated yet. The changes below are not callable until Cobalt activates.
</Warning>

## B20 Asset: scheduled multiplier updates

The B20 Asset multiplier surface becomes conformant with [ERC-8056](https://eips.ethereum.org/EIPS/eip-8056)
and the [B20 Asset multiplier migration details](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20Asset_multiplier.md):

* Adds [`uiMultiplier`, `toUIAmount`, `fromUIAmount`, `balanceOfUI`, and `totalSupplyUI`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20Asset_multiplier.md#functions).
* Adds [`updateUIMultiplier(uint256,uint256)`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20Asset_multiplier.md#scheduled-update-lifecycle) for scheduling corporate-action multiplier updates.
* Retains [`updateMultiplier(uint256)`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20Asset_multiplier.md#updatemultiplieruint256-remains-as-an-instant-admin-failsafe) as an instant administrative failsafe.

Applications should use the ERC-8056 names and move routine multiplier changes to the scheduled
[`updateUIMultiplier`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20Asset_multiplier.md#scheduled-update-lifecycle) function.

## B20 Asset and Stablecoin: seize surface

Cobalt adds [`seizeWithMemo`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20_seize.md#new-at-cobalt-adopt-these),
an administrative balance-reassignment operation gated by [`SEIZE_ROLE`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20_seize.md#functions).
It also adds a [`SEIZE`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20_seize.md#pause-features)
pause vector and two policy slots. [`burnBlocked`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20_seize.md#burnblocked-is-deprecated-but-unchanged-and-still-dialable)
is deprecated in favor of `seizeWithMemo`, but remains callable and unchanged for compatibility.

Seize is opt-in per token and has no effect until the issuer sets
[`SEIZE_HOLDER_POLICY`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20_seize.md#functions).
To destroy supply after a seizure, call [`burn(uint256)`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_B20_seize.md#burnblocked-is-deprecated-but-unchanged-and-still-dialable) separately.

## PolicyRegistry: composite policies

PolicyRegistry adds composite policies that combine two to four existing simple policies using an
OR (`UNION`) or AND (`INTERSECT`) gate. See the [composite policy details](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_PolicyRegistry_composite_policy.md)
for the selector mapping and edge cases. Integrators can create and update them with
[`createCompositePolicy`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_PolicyRegistry_composite_policy.md#new-at-cobalt-adopt-these)
and [`updateComposite`](https://github.com/base/base-std/blob/main/changelog/02_Cobalt_PolicyRegistry_composite_policy.md#new-at-cobalt-adopt-these)
instead of duplicating policy logic off-chain.

Existing `createPolicy` and `createPolicyWithAccounts` integrations do not otherwise change; they
only gain a new revert path for the previously unreachable composite `policyType`.

## Full Base Standard changelog

For selector-level details, including exact function selectors, event topics, error codes, and
edge-case behavior, see the [Base Standard changelog](https://github.com/base/base-std/blob/main/CHANGELOG.md).