frxUSD on Tempo

frxUSD is the first stablecoin to implement Tempo's TIP-20 standard (opens in a new tab) with full support for stablecoin-denominated gas payments and cross-chain reward distribution.

For details on the TIP-20 standard itself, see Tempo's official documentation (opens in a new tab).

Frax's TIP-20 Implementation

Frax is the first to leverage TIP-20's capabilities for:

Stablecoin Gas: Users pay bridge fees in frxUSD—no need to hold native gas tokens
Cross-Chain Supply Tracking: Real-time visibility into frxUSD distribution for reward calculations
TIP-403 Compliance: Protocol-level freeze/thaw via Tempo's policy registry

Architecture

┌─────────────────────────────────────────────────────────────────┐
│                      TEMPO PRECOMPILES                          │
├─────────────────┬─────────────────┬─────────────────────────────┤
│ TIP403_REGISTRY │ STABLECOIN_DEX  │ TIP_FEE_MANAGER             │
│ Policy control  │ Token swaps     │ User gas preferences        │
└────────┬────────┴────────┬────────┴──────────────┬──────────────┘
         │                 │                       │
         ▼                 ▼                       ▼
┌─────────────────────────────────────────────────────────────────┐
│                    FRAX CONTRACTS                               │
├─────────────────────────────────────────────────────────────────┤
│ FrxUSDPolicyAdminTempo     - Freeze/thaw via TIP-403            │
│ FraxOFTMintableAdapterTIP20 - LayerZero bridge with mint/burn   │
│ FraxOFTUpgradeableTempo    - OFT with stablecoin gas payment    │
│ RemoteHopV2Tempo           - Hub routing for cross-chain        │
└─────────────────────────────────────────────────────────────────┘

Key Features

Stablecoin-Denominated Gas

Users pay bridge fees in their preferred stablecoin. The adapter automatically:

Checks the user's preferred gas token via TIP_FEE_MANAGER
If whitelisted: wraps directly via LZEndpointDollar
If not whitelisted: swaps to PATH_USD via STABLECOIN_DEX, then wraps

Users never need to hold native gas tokens to bridge frxUSD.

Cross-Chain Supply Tracking

The SupplyTrackingModule maintains real-time visibility into token distribution across all chains, enabling governance to distribute rewards proportionally based on actual circulating supply:

// Track per-chain supply for reward calculations
function totalSupply(uint32 _eid) external view returns (uint256);
 
// Get transfer flows
function totalTransferFrom(uint32 _eid) external view returns (uint256);
function totalTransferTo(uint32 _eid) external view returns (uint256);

TIP-403 Policy Compliance

Transfer restrictions are enforced at the protocol level via Tempo's TIP-403 Registry (opens in a new tab):

function freeze(address account) external;   // Block account transfers
function thaw(address account) external;     // Unblock account
function isFrozen(address account) external view returns (bool);

Integration Guide

Quoting Bridge Fees

When bridging from Tempo, fees are quoted in the user's preferred stablecoin:

import { SendParam, MessagingFee, IOFT } from "@fraxfinance/layerzero-v2-upgradeable/oapp/contracts/oft/interfaces/IOFT.sol";
import { OptionsBuilder } from "@fraxfinance/layerzero-v2-upgradeable/oapp/contracts/oapp/libs/OptionsBuilder.sol";
 
address oft = 0x...; // FraxOFTUpgradeableTempo address
uint32 dstEid = 30101; // Destination chain EID
uint256 amount = 1e18;
 
bytes memory options = OptionsBuilder.newOptions();
SendParam memory sendParam = SendParam({
    dstEid: dstEid,
    to: bytes32(uint256(uint160(msg.sender))),
    amountLD: amount,
    minAmountLD: amount,
    extraOptions: options,
    composeMsg: '',
    oftCmd: ''
});
 
// Fee returned in user's preferred token, NOT native gas
MessagingFee memory fee = IOFT(oft).quoteSend(sendParam, false);

Sending Cross-Chain

Unlike standard OFTs, Tempo OFTs do not accept msg.value. Fees are paid via ERC-20 approval:

// 1. Approve the OFT to spend fee tokens
IERC20(feeToken).approve(oft, fee.nativeFee);
 
// 2. Send WITHOUT msg.value
IOFT(oft).send(
    sendParam,
    fee,
    payable(msg.sender)  // refund address
);

Reading Supply Data

Query cross-chain supply for analytics or reward distribution:

ISupplyTracking adapter = ISupplyTracking(adapterAddress);
 
// Total sent from this chain
uint256 outflows = adapter.totalTransferFromSum();
 
// Total received on this chain
uint256 inflows = adapter.totalTransferToSum();
 
// Per-chain breakdown
uint256 sentToEthereum = adapter.totalTransferFrom(30101);
uint256 receivedFromArbitrum = adapter.totalTransferTo(30110);
 
// Expected supply on a specific chain
uint256 supplyOnBase = adapter.totalSupply(30184);

Contract Reference

FraxOFTUpgradeableTempo

Tempo-specific OFT with stablecoin gas payment:

Function	Description
`send()`	Bridge tokens (no msg.value)
`quoteSend()`	Get fee in user's preferred token

FrxUSDPolicyAdminTempo

Policy management for compliance:

Function	Description
`freeze(address)`	Block account transfers
`thaw(address)`	Unblock account
`isFrozen(address)`	Check freeze status
`addFreezer(address)`	Grant freeze permissions
`removeFreezer(address)`	Revoke freeze permissions
`policyId()`	Get TIP-403 policy ID

FraxOFTMintableAdapterUpgradeableTIP20

Bridge adapter with supply tracking:

Function	Description
`totalSupply(uint32)`	Expected supply on chain
`totalTransferFrom(uint32)`	Outflows to chain
`totalTransferTo(uint32)`	Inflows from chain
`totalTransferFromSum()`	Total outflows
`totalTransferToSum()`	Total inflows

Events

Supply Tracking

event AddToTotalTransferFromEid(uint32 indexed eid, uint256 previousAmount, uint256 amount);
event AddToTotalTransferFromSum(uint256 previousAmount, uint256 amount);
event AddToTotalTransferToEid(uint32 indexed eid, uint256 previousAmount, uint256 amount);
event AddToTotalTransferToSum(uint256 previousAmount, uint256 amount);
event SetInitialTotalSupply(uint32 indexed eid, uint256 amount);

Policy

event AccountFrozen(address indexed account);
event AccountThawed(address indexed account);
event AddFreezer(address indexed account);
event RemoveFreezer(address indexed account);

Contract Addresses

Testnet (Moderato)

Contract	Address
frxUSD TIP-20	`0x20c000000000000000000000cf5b0F48F7fEDC7F`
FraxOFTMintableAdapterUpgradeableTIP20 (Proxy)	`0x16FBfCF4970D4550791faF75AE9BaecE75C85A27`
FrxUSDPolicyAdminTempo (Proxy)	`0x667daf76CC0fC083B88caa20D8Bd8565884aE97C`
Policy ID	`375842`

Mainnet (Presto) - Coming Soon

Deployment in progress.

Source Code

Overview Addresses