Which USDT does Kraken use?

I'm curious to know which version of USDT, the stablecoin pegged to the US dollar, does Kraken utilize? As a reputable cryptocurrency exchange, it's important to understand the specific implementation of USDT they're offering to their users, given that there are multiple entities and versions of USDT in circulation. Clarity on this matter can help investors and traders make informed decisions about their holdings and transactions on the Kraken platform.