> ## Documentation Index > Fetch the complete documentation index at: https://docs.defindex.io/llms.txt > Use this file to discover all available pages before exploring further. # Stable APY > Publish a rate, and keep what the strategies earn above it. Yield in DeFi floats, and a number that moves every day is a hard thing to put in a savings screen. Stable APY lets you publish one instead: you set a target, and DeFindex adjusts the vault fee so the rate your depositors receive tracks it. The part worth noticing is the upside. Your depositors get the number you advertised, and what the strategies earn above it becomes fee revenue, up to the ceiling you set. Opt in, per vault, and reversible in one call. ## What you are buying A rate you can advertise, and the spread above it. Your app shows one number, it stays put, and the variance is absorbed by your fee rather than by your user's balance. The mechanism is the fee you already control, moved on your behalf. You stay the admin: you set the target, you set the range the fee may travel in, and you are the only one who can take the vault back out. ## When yield runs above target The fee rises and the surplus is captured as vault fees. Your depositors receive the target, and what the strategies earned above it is yours, minus [the DeFindex share](/intro/fees#how-defindex-is-paid). You set a floor and a ceiling when you sign up, and the fee can never leave that range. The limit is enforced by the contract rather than by us remembering it. Moves are gradual and capped, so one odd reading cannot swing your vault. ## When yield runs below target The fee falls toward your floor, step by step, until it gets there. This can only give back yield the strategies actually produced: at a floor of zero your depositors receive all of it and nothing is charged. If that still leaves you short of the target, the only thing that closes the gap is money you put in. That is a separate product: see [Boost](/products/boost), and in particular what the floor you choose here costs you there. ## What DeFindex can do without you Signing up hands us control of one thing, the fee, and nothing else. Exactly how narrow that is: | Action | Who can do it | | -------------------------------- | --------------------------------------------------------------- | | Move the fee, inside your bounds | DeFindex or you. Outside the bounds it reverts | | Change the fee bounds | **Only you** | | Change the target | **Only you** | | Upgrade the vault | **Only you** | | Take the vault back out | **Only you** | | Change how any of this works | **Nobody.** The contract cannot be upgraded, by us or by anyone | One thing DeFindex does on its own: move the fee inside the range you set. Everything else needs your signature. ## Custody Depositors' funds never leave the vault and their withdrawals are never frozen. We move the fee inside your range and nothing else, and leaving hands control straight back to you. See [Risks and Audits](/advanced-documentation/risks-and-audits#custody). ## Availability Mainnet only for now, and enabled per account: the endpoints return `403 Forbidden` until the feature is switched on for your API key. [Contact us on Discord](https://discord.gg/aV5jHwmsaj) to enable it. ## Audit Audited by [Runtime Verification](https://runtimeverification.com/audits) in July 2026, together with the boost treasury. See [Risks and Audits](/advanced-documentation/risks-and-audits). Register a vault, change the target, exit.