I believe this is fixed rate to a certain date of maturity. So differing maturities will have differing rates depending on how far out they are from the date of the loan and the market on the date of the loan.
> When we released our Yield Protocol whitepaper, we called the tokens representing borrowing and lending “yTokens,” after the name of the protocol. Since then, the YFI community has adopted the name yTokens for tokens with completely different purposes. Out of respect for their usage and to avoid any user confusion, we renamed our tokens to “fyTokens.”