Design

B20, and how LUSG uses it.

B20 is Base's native token standard for stablecoins and real-world assets. A token is created by one call to a factory precompile; there is no token contract to write or audit. It is ERC-20 compatible, with roles, policies, pause, supply caps, memos and, for assets, an ERC-8056 multiplier built in.

Precompiles

Precompile	Address	Role
B20 factory	`0xB20f000000000000000000000000000000000000`	`createB20(variant, salt, params, initCalls)`; deterministic addresses starting `0xB200…`
Policy Registry	`0x8453000000000000000000000000000000000002`	Allowlists, blocklists and combined policies, shared across tokens
Activation Registry	`0x8453000000000000000000000000000000000001`	Base's switch for which variants and features are live (all three are on for Vibenet and Base Sepolia)

Upgrade timeline

Source: the B20 changelog on docs.base.org. Denim carries breaking changes for allowlisted tokens; see open questions.

What LUSG uses

B20 feature	LUSG's use
Asset variant, 18 decimals	The token. 18 decimals keeps the multiplier's rounding at one unit in the last place.
`initCalls` at creation	Every role, the cap and the policy bindings were set in the single `createB20` transaction (0x1f4866c0…be5a →).
Roles (`MINT`, `BURN`, `PAUSE`, `UNPAUSE`, `SEIZE`, `METADATA`, `OPERATOR`)	Split across wallets and contracts; see who holds what.
ERC-8056 UI multiplier	Carries the yield. `updateUIMultiplier(m, effectiveAt)` is scheduled every minute by LusgClock. `balanceOf` stays raw; `balanceOfUI` shows dollars.
Policy scopes	One combined policy (KYC allowlist and not sanctions-blocklisted) on `TRANSFER_SENDER`, `TRANSFER_RECEIVER` and `MINT_RECEIVER`.
`SEIZE_EXEMPT_POLICY`	Bound to a treasury-only list. It defaults to always-allow, which exempts everyone; see compliance.
Pause by feature	`TRANSFER`, `MINT`, `BURN`, `SEIZE` pause independently. Base Sepolia adds an auto-pause of mint and redeem on a market gap.
Supply cap	100,000,000 LUSG on Vibenet (raised from 6,000,000 when the desk opened).
Memos (`mintWithMemo`, `seizeWithMemo`)	Each mint and seizure carries a reference for reconciliation, for example a custodian settlement ID.

The multiplier, precisely

Raw and UI. UI balance = raw × multiplier / 1e18. Transfers, allowances and totalSupply stay in raw units.
Absolute values. A multiplier is a level, not a ratio: LUSG's is the basket's dollar value per raw token (1e18 = $1.00).
One pending update. updateUIMultiplier reverts with UIMultiplierUpdateExists while a scheduled value is still in the future; once it takes effect, the next one may be scheduled. No minimum notice and no bound on the size of the move.
No event at the flip. UIMultiplierUpdated(old, new, effectiveAt) fires when an update is scheduled. Indexers should read state at a timestamp.

Creating LUSG

params    = abi.encode((uint8 version = 1, string name, string symbol, address initialAdmin, uint8 decimals = 18))
initCalls = [ grantRole(MINT_ROLE, minter), grantRole(BURN_ROLE, minter),
              grantRole(PAUSE_ROLE, compliance), grantRole(UNPAUSE_ROLE, compliance), grantRole(SEIZE_ROLE, compliance),
              grantRole(METADATA_ROLE, admin), grantRole(OPERATOR_ROLE, clock),
              updateSupplyCap(cap),
              updatePolicy(TRANSFER_SENDER_POLICY, holderPolicy), updatePolicy(TRANSFER_RECEIVER_POLICY, holderPolicy),
              updatePolicy(MINT_RECEIVER_POLICY, holderPolicy), updatePolicy(SEIZE_EXEMPT_POLICY, exemptList) ]
factory.createB20(ASSET = 0, salt, params, initCalls)   // simulate with eth_call first: it returns the address

The token address is deterministic from (variant, sender, salt), so LusgClock was deployed against the predicted address first and received OPERATOR_ROLE inside the same createB20 call.