---
title: "Base Details B20 Seize Functionality and Composite Policies for Cobalt Hardfork"
description: "The upcoming network upgrade introduces administrative balance reassignment and multi-policy authorization rules for asset and stablecoin issuers."
url: https://basisdesk.news/news/base-cobalt-b20-seize-composite-policies
published: 2026-09-30T19:16:16.567Z
modified: 2026-09-30T19:16:16.567Z
section: Tech & Protocols
author: Basis Desk Newsroom (AI-generated, source-verified)
sentiment: neutral
tickers: [ETH]
tags: [Base, Cobalt, Smart Contracts, Compliance, Layer 2]
license: Quote with attribution to Basis Desk (basisdesk.news). Not financial advice.
---

# Base Details B20 Seize Functionality and Composite Policies for Cobalt Hardfork

The upcoming network upgrade introduces administrative balance reassignment and multi-policy authorization rules for asset and stablecoin issuers.

## Key points

- Base's Cobalt hardfork will introduce seizeWithMemo to reassign balances without reducing token supply [1].
- PolicyRegistry will support composite UNION and INTERSECT policies referencing two to four simple child lists [2].
- The legacy burnBlocked function remains dialable, and seize functionality is strictly opt-in per asset [1].

## Editorial remark

- **Context:** Token issuers on Base previously relied on burnBlocked to manage restricted addresses, while combining separate compliance lists required operating custom off-chain synchronization pipelines [1][2].
- **Impact:** Compliance teams and stablecoin issuers on Base gain native tooling to confiscate funds to treasuries and combine multi-tier access rules without duplicating state [1][2].
- **Watch:** Activation dates and testnet deployments for the Cobalt hardfork will dictate when the new selectors become dialable on-chain [1].

Documentation released on Sept. 30 details two major updates coming to the Base network's B20 token specification during the upcoming Cobalt hardfork [1][2]. 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 [1][2].

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].

## FAQ

**Does seizeWithMemo reduce total token supply?**

No. Unlike burnBlocked, seizeWithMemo functions as an administrative transfer from a target account to a specified destination, leaving totalSupply unchanged [1].

**Are existing Beryl policies and functions broken by the Cobalt update?**

No. The changes are backward compatible: burnBlocked remains dialable, and existing simple allowlists and blocklists continue to function normally [1][2].

## Sources

1. [B20: Seize Functionality - Base Documentation](https://docs.base.org/base-chain/specs/reference/b20/changelog/02-cobalt-b20-seize) — docs.base.org, 2026-09-30
2. [PolicyRegistry: Composite Policies (UNION / INTERSECT) - Base Documentation](https://docs.base.org/base-chain/specs/reference/b20/changelog/02-cobalt-policyregistry-composite-policy) — docs.base.org, 2026-09-30

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Basis Desk Newsroom · AI-generated, source-verified · https://basisdesk.news/about/how-we-use-ai