Interest Rate Model - Vanna

Each pool’s borrow rate depends on its utilization u = borrows / (cash + borrows). The curve has three coefficients set by the admin:

annual_rate = rate_multiplier × (linear·u + linear·u^32 + jump·u^64)

At low utilization the linear term dominates, so borrowing is cheap.
As utilization approaches 100%, the u^32 and u^64 terms take over and the rate climbs steeply. That pulls in new lenders and pushes borrowers to repay before the pool runs dry.
An empty pool (u = 0) charges nothing.

The rate is applied per second (SECONDS_PER_YEAR = 31,556,952).

Where interest goes

Interest accrues on every pool touch (and on public_refresh_reserve). A reserve-factor slice goes to accrued_protocol_fees. The rest increases total_borrow_assets, which raises the value of every vToken.

lender APY ≈ borrow APR × utilization × (1 − reserve_factor)

Rounding remainders carry over between accruals, so frequent updates neither overcharge borrowers nor shortchange the treasury. Exact coefficients live on each Reserve account. Read them on-chain rather than assuming defaults.