WRX fuel question

So I bought a 24 WRX a few weeks ago, at the dealer, they told me to only use Preium Fuel, on the cap it only reccomends premium.

My question is therefore, should I only use premium or can I get away with regular? (For now I've only filled it with Premium.) I'm ok if it's required as it's less expensive for a complete fill-up than the Truck I borrowed prior, and I can go further on a full tank.