Full version of legacy Frax Protocol docs are currently available on docs.frax.finance (opens in a new tab)

Crosschain Strategy for Frax Assets

Overview

The Omnichain Fungible Token (OFT) (opens in a new tab) Standard allows fungible tokens to be transferred across multiple blockchains without asset wrapping, middlechains, or liquidity pools.

Frax assets are represented as OFTs on chains other than Fraxtal and Ethereum. An OFT operates the exact same as an ERC20 with the additional function of bridge-ability through the LayerZero protocol.

All OFTs and lockboxes are audited (opens in a new tab) and managed by a Frax multisig on each respective chain (see Multisigs). The LayerZero settings that secure every transfer, including DVNs, block confirmations, and enforced options, are documented under Configuration.

Available Frax OFTs

• frxUSD
• sfrxUSD
• frxETH
• sfrxETH
• WFRAX (prev. FXS)

FPI has been retired from the mesh. FPI OFTs can no longer be bridged.

Contract design

Overall, there are three types of LayerZero contracts that provide liquidity for users upon bridging:

1. OFT

• Operates as an ERC20
• When tokens are received on the chain, the OFT is minted
• When tokens are sent from the chain, the OFT is burned

2. Adapter (aka lockbox)

• Holds a running balance of a Frax-protocol token
• When tokens are received on the chain, the Adapter sends the Frax token from its' balance to the recipient
• When tokens are sent from the chain, the sender sends the Frax token to the Adapter

3. Mintable Adapter (aka mint/burn lockbox)

• Holds no balance of Frax-protocol token
• When tokens are received on the chain, the Mintable Adapter mints the Frax token to the recipient
• When tokens are sent from the chain, the Mintable Adapter burns the Frax token

With the exception of Ethereum, Fraxtal, and frxUSD on Tempo, Frax tokens are represented as an OFT. On those chains, Frax tokens are utilized in the following:

frxUSD

• Fraxtal: Mintable Adapter
• Ethereum: Mintable Adapter
• Tempo: Mintable Adapter (mints and burns the native TIP-20 frxUSD, see Tempo)

sfrxUSD

• Fraxtal: Mintable Adapter
• Ethereum: Mintable Adapter

frxETH

• Fraxtal: Adapter
• Ethereum: Adapter

sfrxETH

• Fraxtal: Adapter
• Ethereum: Adapter

WFRAX

• Fraxtal: Adapter
• Ethereum: OFT

Hub Design

Frax OFTs are wired together as a Hub: every chain has a single connection to Fraxtal, so bridging from chain A to chain B can be seen as A => Fraxtal => B. This reduces the number of connections from N^2 to N.

The Frax team built "Hop" contracts that make the hub invisible to users. With HopV2 (opens in a new tab), the user submits a single transaction on chain A and pays for both legs there. Behind the scenes, bridging from A => B is two LayerZero messages: A => Fraxtal and Fraxtal => B, where the second message is sent automatically by the Fraxtal Hop when the LayerZero Executor calls lzCompose() (opens in a new tab). HopV2 addresses are listed under HopV2 Contracts.

HopV2 replaced the first-generation RemoteHop contracts from fraxtal-lz-hop (opens in a new tab), which are now paused. The MintRedeemHop contracts from that repository remain live for cross-chain frxUSD and sfrxUSD conversions, see Stake & Unstake Supported Networks.

Solana

Solana is the only non-EVM chain in the mesh. Bridging between Solana and Fraxtal is a direct OFT send in either direction, and HopV2 relays transfers to Solana from the other EVM chains in the mesh.

For frxUSD, a single Solana transaction can also reach any other chain in the mesh by sending to the Fraxtal Hop with a compose message (see the lz:oft:send:fraxtalhopv2 task in frax-oft-upgradeable (opens in a new tab)). Other assets bridge from Solana to Fraxtal first, and the user then submits a second transaction from Fraxtal to the destination once the first transfer has settled.

WFRAX vs. FRAX

FRAX is the native gas token on Fraxtal. WFRAX is the wrapped version of FRAX that is used on LayerZero-powered chains, represented as an OFT.

WFRAX vs. FXS on Ethereum

There are two versions of FRAX on Ethereum: WFRAX and FXS. WFRAX is the LayerZero-powered OFT version of FRAX. FXS is the legacy version of FRAX that is not connected to the LayerZero Protocol. FXS is the original version of FRAX that was launched on Ethereum in 2020.

Users only have one option to convert their FXS into FRAX: through the native Optimism bridge.

In order to convert WFRAX to FXS, users must first either:

• If on Fraxtal: unwrap their WFRAX to FRAX.
• If on a LZ-powered chain: bridge WFRAX to Fraxtal to receive FRAX.

From there, users can convert FRAX to FXS on Ethereum through the native Optimism bridge.

Ethereum WFRAX OFT is also connected via the hub model. This means that bridging WFRAX from chain X to Ethereum will be X => Fraxtal => Ethereum. Bridging FXS to chain X will first require the user to bridge FXS to Fraxtal through the native Optimism bridge, converting their FXS to FRAX.

Current Chains

• Fraxtal (hub)
• Abstract
• Arbitrum
• Avalanche
• Base
• BSC
• Ethereum
• Hyperliquid
• Ink
• Katana
• Linea
• Monad
• Optimism
• Plume
• Polygon
• Robinhood
• Sei
• Solana
• Somnia
• Sonic
• Stable
• Tempo
• Unichain
• Worldchain
• X-Layer
• zkSync

See Tempo for TIP-20-specific behavior and stablecoin-denominated gas.

Process

• Bridge through the FUI (link (opens in a new tab))
• Bridge through the Stargate UI (link (opens in a new tab))
• Bridge programatically (see Code)

Security Considerations

Layer Zero OFT Frax Assets are not a liability of the Frax Protocol. They do not appear on the balance sheet on Frax Facts (opens in a new tab). They are not redeemable for protocol owned assets. They are only redeemable for the Frax Asset in the Layer Zero "lockbox" contract that is part of the Layer Zero Protocol.

Layer Zero OFT Frax Assets are settled by Layer Zero Decentralized Verification Networks (DVNs) that are not operated by the Frax Protocol, Frax Core Developers, or any associated entity of Frax. Therefore, the risk of OFT Frax Assets are borne by their holders. This is similar to holding "USDC tokens" on a network that its issuer, Circle, does not support minting/redeeming on. Such "USDC tokens" do not appear on Circle's balance sheet as a liability nor are they redeemable from its issuer. They are only redeemable for the underlying USDC token in the bridge (ie 'lockbox') contract.

In the future, the Frax Protocol can work with Layer Zero to upgrade certain OFT Frax Assets on select networks to allow the Frax Protocol to have direct oversight in the settlement process similar to the Frax Ferry system. After this, the OFT Frax Assets for those select networks will be reported on the associated balance sheet of those Frax Assets. When this occurs, the Frax Protocol will consider such tokens at that time as its liability that are backed directly by the assets it holds on its respective balance sheets. At this time, no Frax OFT tokens are native liabilities of the protocol.