The only fine print at the bottom of their signup page simple says;
“Users of Robinhood Checking and Savings earn 3% interest annually on each of their Checking and Savings balances.”
I would have thought a more precise disclosure would be required. But it certainly does not say anything about fixed, guaranteed, etc.
Presumably when you get to actually creating an account there will be more specific terms which must allow them to adjust the rate in the future.
But it does not seem to be a kind of “teaser” rate. It seems like, I’m guessing, that everyone with a Robinhood Checking account will get the same rate, if they change it in the future it would be a product-wide adjustment.
Most banks in Europe do similar promos, but promo rates are 10x-100x lower, and normal rates rarely exceed 0.1% on saving accounts. Promo rates do typically last 3-6 Months and only for new customers.