# What is sUSDS? Shares in a USDS savings arrangement

sUSDS is the ERC-4626-compatible savings share for USDS in the Sky system. Its share-to-asset conversion reflects the savings-rate accumulator. It is distinct from plain USDS: the rate, contract authority, backing and available exit paths all matter, and a rising USDS-denominated ratio is not a guaranteed dollar return.

Evidence: [Sky Savings Rate](https://developers.skyeco.com/protocol/tokens/susds/); [Savings USDS implementation](https://raw.githubusercontent.com/sky-ecosystem/sdai/dfc7f41cb7599afcb0f0eb1ddaadbf9dd4015dce/src/SUsds.sol); [Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626)

Canonical: https://degreesofsatoshi.com/encyclopedia/what-is-susds/
Published: 2026-10-02
Substantively modified: 2026-10-02
Independently verified by an automated reviewer: 2026-10-02T18:15:23.891Z
Data current through: 2026-10-02

AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied.

## Key facts

- **Standard:** Sky documents an ERC-4626-compatible deposit and withdrawal interface. ([Sky Savings Rate](https://developers.skyeco.com/protocol/tokens/susds/))
- **Accounting:** The implementation uses an accumulator and a savings-rate parameter. ([Savings USDS implementation](https://raw.githubusercontent.com/sky-ecosystem/sdai/dfc7f41cb7599afcb0f0eb1ddaadbf9dd4015dce/src/SUsds.sol))
- **Upgradeability:** The cited design uses a UUPS upgrade pattern. ([Sky Savings Rate](https://developers.skyeco.com/protocol/tokens/susds/))

## Read shares and underlying USDS separately

A deposit exchanges underlying USDS for shares according to the vault’s accounting and rounding. Later, a share can represent a different amount of USDS as the rate accumulator changes.

The share count in a wallet need not increase for the underlying claim to accrue. This differs from a token that directly rebases the displayed balance.

Evidence: [Sky Savings Rate](https://developers.skyeco.com/protocol/tokens/susds/); [Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626)

## A current parameter is not a lifetime promise

The cited implementation exposes authorized parameter-setting logic and rate accumulation. A rate displayed today should be dated and matched to the deployed version.

A worked conversion is useful for understanding the mechanism, but this article intentionally does not quote a current annual return without a fresh verified parameter observation.

Evidence: [Savings USDS implementation](https://raw.githubusercontent.com/sky-ecosystem/sdai/dfc7f41cb7599afcb0f0eb1ddaadbf9dd4015dce/src/SUsds.sol)

## Include the underlying asset and upgrade path

The savings position depends on USDS and on the savings contract’s rules. The documented upgradeability means readers should inspect the actual authority and current implementation.

A share conversion function does not by itself establish secondary-market liquidity or remove the need to inspect withdrawal conditions and the underlying system’s risks.

Evidence: [Sky Savings Rate](https://developers.skyeco.com/protocol/tokens/susds/); [Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626)

## Questions

### Is sUSDS the same token as USDS?

No. USDS is the underlying asset in this savings interface; sUSDS represents the vault-share position that can be converted under the contract’s rules.

Evidence: [Sky Savings Rate](https://developers.skyeco.com/protocol/tokens/susds/); [Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626)

## Claims and scope

### what-is-susds-quick-answer

sUSDS is the ERC-4626-compatible savings share for USDS in the Sky system. Its share-to-asset conversion reflects the savings-rate accumulator. It is distinct from plain USDS: the rate, contract authority, backing and available exit paths all matter, and a rising USDS-denominated ratio is not a guaranteed dollar return.

Scope: {"collection":"stablecoins","dataAsOf":"2026-10-02","blockHeight":null}

### what-is-susds-fact-standard

Standard: Sky documents an ERC-4626-compatible deposit and withdrawal interface.

Scope: {"collection":"stablecoins","dataAsOf":"2026-10-02","blockHeight":null}

### what-is-susds-fact-accounting

Accounting: The implementation uses an accumulator and a savings-rate parameter.

Scope: {"collection":"stablecoins","dataAsOf":"2026-10-02","blockHeight":null}

### what-is-susds-fact-upgradeability

Upgradeability: The cited design uses a UUPS upgrade pattern.

Scope: {"collection":"stablecoins","dataAsOf":"2026-10-02","blockHeight":null}

## Sources

- [Sky Savings Rate](https://developers.skyeco.com/protocol/tokens/susds/) — Sky. Savings-share interface and upgradeable design; parameter values and deployed authority require separate evidence. Locator: sUSDS (Savings USDS); Details. Retrieved: 2026-10-02T17:06:51.378Z.
- [Savings USDS implementation](https://raw.githubusercontent.com/sky-ecosystem/sdai/dfc7f41cb7599afcb0f0eb1ddaadbf9dd4015dce/src/SUsds.sol) — Sky contributors. Savings-rate accumulator, administrator-set rate and share conversions. Locator: ssr; file; drip; convertToAssets. Retrieved: 2026-10-02T17:41:56.801Z.
- [Tokenized Vaults](https://eips.ethereum.org/EIPS/eip-4626) — Ethereum Improvement Proposals. Assets, shares, deposits, withdrawals, limits and preview rounding. Locator: Specification; Security Considerations. Retrieved: 2026-10-02T17:03:42.366Z.

## Revision history

- 2026-10-02: First publication after primary-source research and independent automated verification.

## Cite this entry

Degrees of Satoshi editorial project. “What is sUSDS? Shares in a USDS savings arrangement.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/what-is-susds/