B20 Native Token Standard

B20 is Base’s native token standard - designed for stablecoin issuers, real-world asset (RWA) and equity issuers, and long-tail token creators.

B20 is the Base ecosystem’s own version of ERC-20. It ships with a built-in compliance toolkit: transfer policies, freeze-and-seize, role-based access control, memos, and supply caps. The full interface specs are available in the Base Standard Library repository.

B20 supports two variants:

Variant	Decimals	Additional Features
Asset	6–18 (configurable)	Rebase multiplier, onchain announcements, batched issuance
Stablecoin	6 (fixed)	Self-declared fiat currency code

ERC-20 Compatibility

B20 tokens are implemented as Rust precompiles rather than EVM smart contracts, making them faster, cheaper, and more native to the chain. All tokens are deployed via the singleton IB20Factory precompile.

B20 implements the full ERC-20 standard surface with complete selector parity - it is a drop-in replacement for existing tooling and integrations.

Roles Model

B20 role-based access control extends OpenZeppelin AccessControl with a fixed set of roles and one behavioral override on admin renunciation.

Role	Gates
DEFAULT_ADMIN_ROLE	All admin operations: role grants, policy updates, supply-cap changes
MINT_ROLE	mint, mintWithMemo
BURN_ROLE	Caller-side burns: burn, burnWithMemo
BURN_BLOCKED_ROLE	Third-party burns against policy-blocked accounts: burnBlocked
PAUSE_ROLE	pause
UNPAUSE_ROLE	unpause
METADATA_ROLE	updateName, updateSymbol, updateContractURI

User-defined roles are supported via setRoleAdmin and grantRole. They carry no built-in effect - B20 only enforces gates against the seven roles above.

Admin Renunciation

The last DEFAULT_ADMIN_ROLE holder cannot be removed via renounceRole or revokeRole (both revert with LastAdminCannotRenounce). The dedicated renounceLastAdmin() is the only path to permanently transition a token to admin-less.

Tokens that intend to launch admin-less from the start pass initialAdmin == address(0) at creation, which never grants the role and skips the renounceLastAdmin step entirely.

After renounceLastAdmin() (or for tokens deployed with initialAdmin == address(0)):

• Operations gated by DEFAULT_ADMIN_ROLE become permanently uncallable.
• Roles already granted to other addresses (MINT_ROLE, BURN_ROLE, etc.) continue to function independently.
• Admin resurrection is blocked: grantRole, revokeRole, and setRoleAdmin all revert with AccessControlUnauthorizedAccount even if the caller holds a custom role.

Policy Registry

The PolicyRegistry is a singleton precompile that manages allowlists and blocklists. B20 tokens reference policies by uint64 ID. Any caller can create a policy and nominate its admin.

State-changing functions on the PolicyRegistry are gated by the ActivationRegistry, which tracks which Base features are live. Read functions (isAuthorized, policyExists, policyAdmin, pendingPolicyAdmin) are always callable.

Policy Types

Type	Default	Behavior
BLOCKLIST	Authorized	All accounts authorized by default; explicitly listed accounts are denied.
ALLOWLIST	Denied	All accounts denied by default; explicitly listed accounts are authorized.

Policy IDs

Policy IDs are uint64 values. The top byte encodes the PolicyType; the low 56 bits are a global counter starting at 2.

Two built-in IDs require no creation:

Constant	ID	Behavior
ALWAYS_ALLOW	0	Authorizes every account unconditionally. Default scope value on new B20 tokens.
ALWAYS_BLOCK	(uint64(ALLOWLIST) << 56) | 1	Denies every account unconditionally.

isAuthorized never reverts on a non-existent policy ID - it collapses to empty-member-set semantics (non-existent BLOCKLIST authorizes everyone; non-existent ALLOWLIST denies everyone).

Consumers that write a policy ID (e.g. updatePolicy) MUST validate policyExists(policyId) at write time to avoid silently binding to an unintended empty-set policy.

Admin Model

Each policy has one admin. Admin transfers are two-step: the current admin calls transferPolicyAdmin(policyId, newAdmin), then the pending admin calls acceptPolicyAdmin(policyId). renouncePolicyAdmin(policyId) permanently freezes the policy - membership can never be changed again.

Creating and Managing Policies

// Create a policy
uint64 policyId = policyRegistry.createPolicy(PolicyType.BLOCKLIST, adminAddress);

// Update membership (batched)
policyRegistry.addToPolicy(policyId, accounts);
policyRegistry.removeFromPolicy(policyId, accounts);

Read Interface

Method	Description
isAuthorized(policyId, account)	Whether account is authorized under policyId. Never reverts.
policyExists(policyId)	Whether a policy with this ID has been created.
policyAdmin(policyId)	Current admin address.
pendingPolicyAdmin(policyId)	Pending admin during a two-step transfer.

Policy Integration

B20 declares a fixed set of policy scopes. Each scope stores a uint64 policy ID pointing into the PolicyRegistry. On every gated operation, B20 calls isAuthorized against the relevant scope and reverts with PolicyForbids if the account is not authorized.

Scope	Gates
TRANSFER_SENDER_POLICY	The from of transfer / transferFrom
TRANSFER_RECEIVER_POLICY	The to of transfer / transferFrom
TRANSFER_EXECUTOR_POLICY	The msg.sender of transferFrom (not checked on transfer)
MINT_RECEIVER_POLICY	The to of mint

approve is not policy-gated - only actual balance movement via transfer / transferFrom is checked.

Every scope defaults to ALWAYS_ALLOW at token creation unless overridden in the bootstrap initCalls. An unattended B20 deployment is fully open - token behavior must be intentionally constrained.

Scopes are read via policyId(scope) and written via updatePolicy(scope, policyId). updatePolicy is admin-gated and reverts if the scope is not recognized.

Mint

New supply is created via mint / mintWithMemo, gated by MINT_ROLE. The recipient is policy-checked against MINT_RECEIVER_POLICY. The operation reverts with SupplyCapExceeded if it would push totalSupply past the cap.

Burn

Two burn paths exist:

• burn / burnWithMemo - caller burns from their own balance. Gated by BURN_ROLE.
• burnBlocked - burns from a third party’s balance. Gated by BURN_BLOCKED_ROLE. The target account MUST be denied by TRANSFER_SENDER_POLICY - this is the freeze-and-seize path for regulated issuers.

Supply Cap

The supply cap is optional. The sentinel type(uint256).max indicates no cap (the default at creation). updateSupplyCap(newCap) is admin-gated and emits SupplyCapUpdated. Lowering below the current totalSupply reverts with InvalidSupplyCap.

Memos

A memo is an optional bytes32 payload attached to a token operation for off-chain reference. Every memo-emitting operation emits Memo(address indexed caller, bytes32 indexed memo) immediately after the operation’s primary event. Indexers join via (transactionHash, logIndex − 1).

Memo-emitting entrypoints: transferWithMemo, transferFromWithMemo, mintWithMemo, burnWithMemo.

Pause

Pauses are granular: the PausableFeature enum partitions the token surface into independently pausable operations - TRANSFER, MINT, and BURN. The enum is append-only. pause(features) and unpause(features) are gated by separate roles (PAUSE_ROLE and UNPAUSE_ROLE) by design.

ERC-2612 Permit / EIP-712

B20 implements ERC-2612 (signed approvals) using an EIP-712 domain shaped as (name, version, chainId, verifyingContract), with version fixed at "1". updateName rotates the domain separator and emits EIP712DomainChanged (ERC-5267). ERC-1271 contract signatures are not accepted - ECDSA only.

Contract URI (ERC-7572)

contractURI() returns a string pointing to off-chain metadata per ERC-7572. updateContractURI(newUri) is gated by METADATA_ROLE.

Metadata Updates

METADATA_ROLE gates:

• updateName(newName) - updates name and rotates the EIP-712 domain separator. Emits NameUpdated and EIP712DomainChanged.
• updateSymbol(newSymbol) - updates symbol only. Emits SymbolUpdated.

Factory

All B20 tokens are created through the singleton IB20Factory precompile via createB20(variant, params, initCalls, salt).

Parameter	Description
variant	ASSET or STABLECOIN
params	ABI-encoded, variant-specific creation struct (versioned by leading byte)
initCalls	Optional array of ABI-encoded calls dispatched post-creation with admin privilege bypass
salt	Caller-chosen entropy for address derivation

Address Derivation

B20 addresses are deterministic and encode the variant directly:

[10-byte B20 prefix][1-byte variant][9-byte keccak256(deployer, salt)]

The variant is recoverable from the address alone without an RPC call. Helper functions getB20Address(variant, deployer, salt), isB20(addr), and isB20Initialized(addr) are available on the factory.

initCalls Semantics

initCalls are dispatched after token creation with admin privilege bypass, allowing configuration (e.g. setting policies, granting roles) in the same transaction as deployment. The bypass is partial:

• MINT_RECEIVER_POLICY is always enforced even during initCalls.
• Pause state is never bypassed.
• Token invariants (supply cap, etc.) are never bypassed.

Variants

Asset

The general-purpose variant for assets of all kinds. Decimals are configurable between 6 and 18 at deployment time and are immutable after creation.

In addition to the base B20 surface, Asset tokens add an OPERATOR_ROLE that gates the following capabilities:

Multiplier

A WAD-precision rebase multiplier applied to all balance reads. Raw balances are stored unchanged; the multiplier scales the view returned to callers.

Method	Description
multiplier()	Current WAD-precision multiplier
scaledBalanceOf(account)	Raw balance × multiplier
toScaledBalance(raw)	Convert raw amount to scaled
toRawBalance(scaled)	Convert scaled amount to raw
updateMultiplier(newMultiplier)	Update the multiplier. Gated by OPERATOR_ROLE.

Announcements

On-chain disclosure brackets that wrap sensitive operations (e.g. batch mints, multiplier updates) with a public notice period. Gated by OPERATOR_ROLE.

announce(internalCalls, id, description, uri) emits an Announcement event, executes internalCalls, then emits EndAnnouncement. The id must be unique and is enforced forever. Inner call reverts are wrapped in InternalCallFailed.

Batch Mint

batchMint(recipients, amounts) mints to multiple recipients in a single call. Gated by MINT_ROLE. Should be wrapped in announce() for transparency.

Extra Metadata

An arbitrary key/value store for issuer-defined on-chain metadata.

Method	Description
extraMetadata(key)	Read a value by key
updateExtraMetadata(key, value)	Write a value. Gated by METADATA_ROLE. Setting an empty value removes the entry.

Stablecoin

The fixed-decimals, fiat-backed carveout. Decimals are hard-wired to 6 and are not configurable.

Adds currency(), which returns an ISO-style currency code string (e.g. "USD", "EUR"). The code is set once at creation via B20StablecoinCreateParams.currency, restricted to characters A-Z only. It is self-declared and not verified against any external registry.