> For the complete documentation index, see [llms.txt](https://docs.kpk.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.kpk.io/funds/infrastructure/onchain-accounting/price-feeds/susds.md).

# sUSDS

Custom price feed for **Sky/MakerDAO Savings USDS**. sUSDS is an ERC-4626 vault share that accrues value as the Sky Savings Rate (SSR) accumulates. The price is derived from the vault's current share-to-asset conversion rate multiplied by the Chainlink USDS/USD feed.

**Source:** [`sUSDS_CustomPriceFeed.sol`](https://github.com/karpatkey/onchain-accounting/blob/main/src/prices/protocols/sUSDS_CustomPriceFeed.sol)

***

## Approach

`sUSDS.convertToAssets(1 sUSDS)` × USDS/USD (from the NAV's primary feed)

{% hint style="info" %}
The USDS/USD term is sourced from the NAV's own selector — see [Base/USD from the NAV's own selector](/funds/infrastructure/onchain-accounting/price-feeds.md#base-usd-from-the-navs-own-selector).
{% endhint %}

<figure><img src="/files/5qVQm18AuT4E0cf16tJl" alt="Left-to-right flowchart of the sUSDS price feed: rate and Chainlink inputs combine into a USD price, with a staleness gate."><figcaption><p>sUSDS price feed — how its oracle inputs compose into a USD price, with the staleness gate.</p></figcaption></figure>

***

## Price calculation

```
decimals = sUSDS.decimals()                       // vault share decimals
rate     = sUSDS.convertToAssets(10^decimals)     // USDS per 1 sUSDS (vault decimals)
price    = rate × USDS_USD / 10^decimals
```

| Input               | Source                                              | Description                                                    |
| ------------------- | --------------------------------------------------- | -------------------------------------------------------------- |
| `convertToAssets()` | `IERC4626(sUSDS)`                                   | USDS backing per 1 sUSDS share at the current SSR-accrued rate |
| `USDS_USD`          | NAV base — `getPriceDataNoDivergence(USDS)` (8 dec) | the NAV's primary USDS/USD price                               |

The ERC-4626 `convertToAssets` call returns the current exchange rate including all accrued Sky Savings Rate interest. The vault decimals are read once at deploy. Result carries the feed's **8 decimals**. The USDS/USD term is read from the NAV's primary feed.

***

## Constructor

```solidity
constructor(
    address sUsds_,
    address nav_,
    address baseAsset_
)
```

| Parameter    | Description                                                                                                                                 |
| ------------ | ------------------------------------------------------------------------------------------------------------------------------------------- |
| `sUsds_`     | The sUSDS vault address (also used to read vault decimals)                                                                                  |
| `nav_`       | NAVCalculator (proxy) — supplies the base stablecoin's USD price via `getPriceDataNoDivergence`                                             |
| `baseAsset_` | The registered base stablecoin whose USD price is read (USDS); **must equal the vault's `asset()`** — reverts `BaseAssetMismatch` otherwise |

***

## Staleness

The price is stale if the NAV reports the base asset (USDS) stale — all its feeds stale. The base leg's `updatedAt` comes from the NAV's selected USDS feed. The `convertToAssets` rate has no heartbeat — it is a live view on the ERC-4626 vault.

***

## Chains

Deployed on **Ethereum mainnet** only.


---

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