Fira supports variable-rate lending and borrowing through the SisuVault and a standard lending market with oracle-enforced LTV.
Overview
Fira's variable-rate market operates alongside the fixed-rate system. Borrowers post collateral (wstETH, cbBTC) and borrow USDC at a variable rate that adjusts based on utilization. Lenders deposit USDC into the SisuVault (an ERC-4626 vault) to earn variable yield.
FW tokens rehypothecate part of their underlying into the variable-rate market on the supply side. This means FW depositors indirectly earn variable-rate lending yield in addition to any other yield sources.
How it works
Lending (supplying)
Users deposit USDC into the SisuVault and receive vault shares (mkUSDC). The vault aggregates deposits and supplies them across lending markets. Yield accrues as borrowers pay interest, increasing the vault's share price over time.
Borrowing
Borrowers interact directly with the Variable Rate LendingMarket:
Approve collateral token to the lending market
Supply collateral via supplyCollateral(marketParams, amount, user, "")
Borrow via borrow(marketParams, usdcToBorrow, 0, user, receiver)
Interest accrues continuously based on the AdaptiveCurveIrm interest rate model, which adjusts rates based on utilization.
Repaying
Borrowers approve USDC to the lending market and call repay(marketParams, assets, 0, user, ""). The position's borrow balance is reduced accordingly.
Supported collateral
Collateral
LTV
LLTV
Oracle
wstETH
87%
89%
Morpho wstETH/USDC
cbBTC
88%
90%
ChainlinkOracleV2 (BTC/USD + USDC/USD)
Key features
Variable yield for lenders — Earn yield proportional to vault share ownership
Multiple collateral types — wstETH and cbBTC supported
Adaptive interest rates — Rates adjust based on market utilization
Permissionless — No whitelist required for variable-rate markets
ERC-4626 vault — Standard vault interface for composability
