Folks have waited a long time for Stadia to deliver the free tier it promised so many moons ago. Yep, right now you need premium for the privilege of using Stadia, but that changes today...sort of.
It's not the full-time free tier we were expecting, but Phil Harrison, VP and GM of the Stadia project, has confirmed that "anyone who signs up will get two free months of Stadia Pro with instant access to nine games." Existing subscribers "won't be charged for the next two months."
After that period is over your subscription will revert back to the Stadia Pro option for $10 a month. That wording, mind, implies that the free Stadia tier is still at least a few months out.