> For the complete documentation index, see [llms.txt](https://docs.fira.money/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fira.money/developers/protocol-contracts/lending.md).

# Lending

## Overview

Fira uses two lending market deployments:

### FiraLendingMarket (Fixed-Rate)

* **Loan token:** BT (Bond Token)
* **Collateral:** Pendle PT tokens (PT-USDe, PT-sUSDe, PT-USDG)
* **Interest rate model:** None (`IRM = address(0)`) — the rate is implicit in the BT discount
* **Supply:** Whitelist-gated to the LiquidityInjector only
* **Oracle:** FiraSolvencyOracle (3-layer oracle pipeline)

### VariableLendingMarket (Variable-Rate)

* **Loan token:** USDC
* **Collateral:** wstETH, cbBTC
* **Interest rate model:** AdaptiveCurveIrm (adjusts based on utilization)
* **Supply:** Permissionless via SisuVault (ERC-4626)
* **Oracle:** Morpho wstETH/USDC, ChainlinkOracleV2 for cbBTC/USDC

## SisuVault

The SisuVault is an ERC-4626 vault that aggregates USDC deposits and supplies them to variable-rate lending markets. It is managed by a curator and allocator (Markov Labs) who control market allocation.

Vault shares (`mkUSDC`) represent proportional claims on the underlying USDC plus accrued interest.

## Key functions

| Function                                             | Description                            |
| ---------------------------------------------------- | -------------------------------------- |
| `supplyCollateral(params, amount, user, data)`       | Deposit collateral                     |
| `borrow(params, assets, shares, user, receiver)`     | Borrow loan token                      |
| `repay(params, assets, shares, onBehalf, data)`      | Repay debt                             |
| `withdrawCollateral(params, amount, user, receiver)` | Withdraw collateral                    |
| `liquidate(params, borrower, seizedAssets)`          | Liquidate undercollateralized position |
| `getUserPosition(params, user)`                      | View full position details             |
| `accrueInterest(params)`                             | Update interest state                  |

## Related pages

* [Fixed-Rate Lending (Feature)](https://github.com/Pi-2lavega/fira-gitbook-sync-final/blob/main/developers/smart-contracts/overview/features/fixed-rate-lending.md)
* [Variable-Rate Lending (Feature)](https://github.com/Pi-2lavega/fira-gitbook-sync-final/blob/main/developers/smart-contracts/overview/features/variable-rate-lending.md)
* [Contract Deployments](https://github.com/Pi-2lavega/fira-gitbook-sync-final/blob/main/developers/smart-contracts/protocol-contracts/contract-deployments.md)


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