Spark has opened its USDT savings vault to OKX customers, giving eligible users of the centralized exchange a way to earn onchain yield on their stablecoin balances from inside the OKX app, according to a statement the company shared with The Defiant before publication.
The setup sends exchange-held stablecoins into an onchain vault without requiring users to open a wallet or bridge funds on their own. OKX aggregates customer deposits and routes them into Spark Savings USDT on X Layer, OKX’s Ethereum Layer 2, instead of having each user hold the vault token directly. Spark told The Defiant that those deposits go into the same vault contract available to any X Layer user, not a segregated pool created only for OKX.
Vault rate and current size
The vault pays 3.5%, based on the savings rate stored in the vault contract on X Layer. That is the same rate set on Spark’s Ethereum USDT vault. For comparison, DefiLlama showed Aave’s Ethereum USDT market paying a base supply rate of 3.72% on Thursday. Spark declined to provide a rate before launch, citing legal restrictions.
Nearly all of Spark’s USDT deposits sit on Ethereum, where the vault held $359.9 million. In written answers to The Defiant, Spark put total USDT savings at about $361 million.
X Layer parameters
According to parameters added to the Spark Artifact in July, Spark governance set the X Layer vault’s supply cap at 750 million USDT and its maximum yield at 6%. L2BEAT shows X Layer securing $130.4 million in total, which puts the cap at close to six times the value currently on the chain.
Spark targets a liquidity buffer on X Layer equal to the greater of 10% of deposits or $1 million, with a ceiling of $10 million. The remainder is bridged back to Ethereum for deployment. Instant withdrawals are handled from that buffer.
Deposits enter as USDT0
Spark’s documentation says the deposit asset on X Layer is USDT0, the omnichain version of Tether’s dollar token issued through LayerZero. Native USDT is used as the deposit asset only on Ethereum.
Spark’s Liquidity Layer moves pooled capital across approved venues that include SparkLend, Morpho vaults and real-world asset strategies. Earlier this year, Spark added institutional lending products and seeded a stablecoin trading layer on Uniswap v4 with $150 million. For every dollar deposited into Spark Savings, Spark borrows an equivalent amount of USDS through Sky’s allocation system, which gives the vault 1:1 USDS backing.
Sam MacPherson, Spark’s co-founder and chief executive, said in the release: 「OKX provides the familiar exchange experience, X Layer provides the on-chain environment connecting that experience to DeFi, and Spark provides the allocation intelligence that coordinates capital across approved lending, liquidity and credit opportunities.」
Jason Lau, OKX’s chief innovation officer, said routing the product through X Layer 「means eligible USDT holders can access a meaningfully differentiated savings product without any of the traditional DeFi onboarding overhead.」
How losses would be absorbed
Spark said savings deposits rank alongside USDS holders in the Sky ecosystem’s loss hierarchy. Losses would first hit Spark’s junior risk capital, then Sky’s surplus buffer, then excess capital held across Sky entities, and then newly issued SKY tokens.
If those layers are exhausted, any remaining deficit would be socialized across USDS holders, and Sky could set the USDS target price below $1, according to Spark’s security framework.
Spark’s own risk reviewers also highlighted the chain-level risk attached to where the deposits land. In July, when the Spark Risk Council cleared the deployment for a vote, it wrote that X Layer lacks a sufficiently decentralized proof system, so 「security of the funds relies heavily on the operator which can also instantly upgrade the chain」. L2BEAT places X Layer in its “others” category for the same reason.
The council responded by capping exposure with a $5 million maximum transaction size on outbound flows from Ethereum. It also noted that even if a relayer were compromised, the vault yield could not be set above 6%. BA Labs, the Core Council and Sky’s risk function set the X Layer buffer at a 100% capital requirement ratio until the chain could be reviewed further.
Approved in July, disclosed now
Phoenix Labs proposed spUSDT on X Layer on July 6, alongside rate limits for bridging USDT from Ethereum. Both items then went to a joint Snapshot poll for the July 16 spell. By July 20, the vault was already live, and governance had moved to record its onchain parameters. Spark’s documentation says new chain deployments and protocol integrations require governance approval.
No proposal, however, names OKX as a distribution partner.
Availability and broader footprint
According to the release, Spark Savings USDT will be available to eligible OKX users outside the European Union. In responses to The Defiant, Spark representatives said the product is available globally except for countries in the European Economic Area and other jurisdictions restricted by OKX.
DefiLlama shows Spark holding $6.47 billion in total value locked across Ethereum, Base, Arbitrum, Robinhood Chain and Gnosis. CoinGecko data showed SPK trading at $0.0189 on Thursday, down 4% on the day and up 34.3% over the past 30 days, for a market value of about $62 million.
The two companies said they are considering additional integrations.