Spark Savings USDT vault nearly doubles to $600 million in two weeks

Spark Savings USDT has nearly doubled its deposits to $600 million in just two weeks. In stablecoin yield products, that counts as a sprint.

The vault lets people park USDT and earn a variable yield, paid back in USDT.

What the vault actually does

Spark Savings USDT is a non-custodial vault built on the ERC-4626 standard. Non-custodial means Spark does not hold users’ funds the way a bank holds deposits. Users keep control through smart contracts. When they deposit, they receive a vault token called spUSDT, which represents their share of the pool.

Behind the scenes, the vault is backed 1:1 by USDS. It uses the Spark Liquidity Layer to route assets into lending venues, including SparkLend. The yield comes from lending activity, which is why the rate floats rather than sitting still.

The vault runs on Ethereum and also supports other chains, including Arbitrum and X Layer. Spark offers sibling products too, such as spUSDC and sUSDS, for users holding other dollar tokens.

The numbers behind the run

The vault’s total value locked, or TVL, has been reported moving between $400 million and $605 million.

Yields tell a slightly different story. The annual percentage yield on the USDT vault has been reported in a range of 3% to 3.75%, with other reports placing it at 3.5% to 3.75%. Earlier peak rates exceeded 4%.

So the rate has come down from its highs while deposits have climbed. That pattern is common in lending pools. When more money pours in chasing the same pool of borrowers, each dollar tends to earn a little less.

The OKX effect

In September 2026, the OKX app integrated Spark Savings, letting users earn on-chain yield on their USDT balances directly inside the exchange’s app.

The integration aggregates user deposits into the vault. Users do not need to bridge tokens between chains or connect a separate wallet.

The research ties the vault’s significant 2026 growth partly to this integration. It improved both engagement and accessibility for exchange customers who already held USDT and wanted it to do something.

Stress-tested, at least once

Spark emphasizes conservative liquidity buffers and risk parameters. Those buffers were tested during market stress in April 2026, in an incident involving rsETH. The vault maintained its liquidity through that episode.

What this means

The trade-off is the rate. With reported APYs below the earlier peak of over 4%, new depositors are getting a lower return than early ones did. If inflows keep outpacing borrowing demand, that compression could continue.

The vault depends on smart contracts, on the health of the USDS backing, and on the lending venues where the Spark Liquidity Layer deploys funds. Non-custodial does not mean risk-free. It means the risks live in code and collateral rather than in a bank’s balance sheet.