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USTB 4626 Redeemer #178

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4 changes: 4 additions & 0 deletions pages/frxusd/mint-and-redeem-overview.mdx
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Expand Up @@ -33,6 +33,10 @@ Get started with the following quickstarts:
- [Mint and redeem with WisdomTree's WTGXX](/frxusd/mint-and-redeem-quickstarts/wtgxx)
- [Mint and redeem with Bridge.xyz's USDB](/frxusd/mint-and-redeem-quickstarts/usdb)

### Direct frxUSD → USDC Redemption

frxUSD can also be redeemed directly for USDC in a single transaction via the [ERC4626RedeemUSTB contract](/frxusd/mint-and-redeem-routes#direct-frxusd--usdc-redemption-via-ustb), which routes the redemption through Superstate's USTB behind the scenes — no USTB onboarding required.

## Cross-Chain Minting & Redeeming with FraxNet

### Overview
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2 changes: 2 additions & 0 deletions pages/frxusd/mint-and-redeem-quickstarts/ustb.mdx
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Expand Up @@ -9,6 +9,8 @@ This guide demonstrates how to use the viem framework in a simple script that en

**Note:** Please ensure the sender and recipient addresses are onboarded to hold **USTB**.

**Tip:** If you only want to redeem frxUSD for **USDC** (without holding USTB yourself), you can use the [Direct frxUSD → USDC Redemption contract](/frxusd/mint-and-redeem-routes#direct-frxusd--usdc-redemption-via-ustb) instead, which routes through USTB in a single transaction.

## Prerequisites

Before you start building the sample app to perform a frxUSD transfer, ensure you have met the following prerequisites:
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36 changes: 36 additions & 0 deletions pages/frxusd/mint-and-redeem-routes.mdx
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Expand Up @@ -29,6 +29,42 @@ The following table shows the supported assets you can use to mint and redeem fr
- [Mint and redeem with WisdomTree's WTGXX](/frxusd/mint-and-redeem-quickstarts/wtgxx)
- [Mint and redeem with Bridge.xyz's USDB](/frxusd/mint-and-redeem-quickstarts/usdb)

## Direct frxUSD → USDC Redemption via USTB

The **ERC4626RedeemUSTB** contract allows frxUSD holders to redeem frxUSD directly for **USDC** in a single transaction, routing the redemption through Superstate's USTB. Because USTB only passes through the contract itself, the caller does **not** need to hold USTB — you only touch frxUSD and USDC.

| Contract | Address |
| ---------------------- | ----------------------------------------------------------------------------------------------------------------------- |
| **ERC4626RedeemUSTB** | [`0x00000000564ee6a571C5819057f27bb671E78Bd5`](https://etherscan.io/address/0x00000000564ee6a571c5819057f27bb671e78bd5) |

### How It Works

When you call `redeem`, the contract atomically:

1. Pulls frxUSD from your wallet (requires a prior frxUSD approval to the contract)
2. Redeems the frxUSD for **USTB** via the [USTB Mint & Redeem custodian](https://etherscan.io/address/0x5fbAa3A3B489199338fbD85F7E3D444dc0504F33)
3. Redeems the USTB for **USDC** via [Superstate's USTB redemption contract](https://etherscan.io/address/0x4c21B7577C8FE8b0B0669165ee7C8f67fa1454Cf)
4. Transfers the resulting USDC to your chosen receiver address

### Key Functions

The contract exposes an ERC-4626-style interface where **frxUSD is the share token** and **USDC is the underlying asset**:

| Function | Description |
| --------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------- |
| `redeem(uint256 _sharesIn, address _receiver, address _owner)` | Redeems an exact amount of frxUSD for USDC. `_owner` must be the caller. |
| `withdraw(uint256 _assetsOut, address _receiver, address _owner)`| Withdraws an exact amount of USDC by burning the required frxUSD. `_owner` must be the caller. |
| `previewRedeem(uint256 _sharesIn)` | Simulates how much USDC a given amount of frxUSD would return. |
| `previewWithdraw(uint256 _assetsOut)` | Simulates how much frxUSD is needed to receive a given amount of USDC. |
| `maxRedeem(address _owner)` / `maxWithdraw(address _owner)` | Returns the maximum frxUSD redeemable / USDC withdrawable for an address given current capacity. |
| `totalAssets()` | Total USDC currently available via this route. |

**Notes:**

- This is a **redeem-only** contract — deposit and mint functions are not supported and will revert. To mint frxUSD, use the [Mint & Redeem contracts](#mint--redeem-routes-on-ethereum) above.
- Redemption capacity is bounded by the USTB held in the custodian and the instant USDC liquidity available in Superstate's redemption contract. Use `maxRedeem` / `maxWithdraw` to check current capacity before redeeming.
- The contract is an upgradeable ERC-1967 proxy (`Frax1967Proxy`); its current implementation is [`ERC4626RedeemUSTB`](https://etherscan.io/address/0x4Ffd2fB49dc1386288e58040B65d6b76B56699cE).

## Cross-Chain Mint & Redeem Routes

The FraxNet contract system allows for cross-chain frxUSD mint & redeem operations. This system enables minting and redeeming frxUSD across multiple networks using **USDC**. The same factory contract powers [FraxNet](https://net.frax.com):
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