Integrate USDh

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Holding and moving USDh

• Use the proxy address 0xbcFC42391e55484129191eDfcC766a2c6F9eb503. Never the implementation address behind it.
• 6 decimals, like USDC. Read decimals() rather than hard-coding it.
• Gasless approvals. EIP-2612 permit. The signing domain is name USDh, version 1, chain ID 1.
• Gasless transfers. EIP-3009 transferWithAuthorization and receiveWithAuthorization, with a random 32-byte nonce and a valid-after and valid-before time window. Signatures from contract wallets such as Safes work through EIP-1271. An unused authorization can be cancelled with cancelAuthorization.

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When a transfer can fail

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Minting and redeeming as an approved route

• Approval is per calling address. Minting and redeeming are approved separately. The contract checks the address that calls it, not the one receiving USDh.
• Mint. Approve the stablecoin to the USDh contract, then call mintWithStable(stable, stableAmount, to). USDh is minted to to, 1:1, in the same transaction. The accepted stablecoins are listed by supportedStables().
• Redeem. Call redeemForStable(stable, usdhAmount, to). USDh is burned from the caller and the stablecoin is sent to to, 1:1.
• Redemption limit. Each address has its own limit every 7 days, checked by effectiveRedeemCap(address). By default it is set to half the balance of the address USDh is minted to. If your contract mints to your users rather than to itself, ask Hamilton to set your limit, or redeeming fails with redeem cap not set.
• No cap on minting with stablecoins. The daily ceiling applies only to minting against bank wires.

interface IUSDh {
    function mintWithStable(address stable, uint256 stableAmount, address to) external;
    function redeemForStable(address stable, uint256 usdhAmount, address to) external;
    function supportedStables() external view returns (address[] memory);
    function effectiveRedeemCap(address user) external view returns (uint256);
    function mintWhitelist(address user) external view returns (bool);
    function redeemWhitelist(address user) external view returns (bool);
    function frozen(address account) external view returns (bool);
    function paused() external view returns (bool);
}

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Events to watch

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Go-live checklist

1. You use the proxy address from Contracts.
2. You read decimals() from the contract.
3. Your app handles a paused system and a frozen address without breaking.
4. You watch the timelock for scheduled changes to USDh.
5. For approved routes: Hamilton has confirmed which of your addresses can mint and which can redeem.
6. For approved routes: you have tested a small mint and a small redemption, and your redemption limit is set.
7. For approved routes: your sanctions screening matches what your agreement with Hamilton requires.