Niantic has come around to make some clarifications to the upcoming community day, mostly in regards to trainer battles.
It began when a Twitter user asked two questions regarding the upcoming Community Day. The first was whether the Sinnoh stones were guaranteed drops or the “chance to get them.” The second asks whether or not the trainer battles include team leaders.
Niantic replied to the tweet, explaining that trainers “have the possibility of earning up to 5 Rewards (instead of the usual 3) from Trainer Battles, although the chances of getting a Sinnoh Stone are still random.”
They then respond to themselves, clarifying further.
“On February 16 and 17, Trainer Battle rewards will increase from 3 to 5 on both days. During your region’s Community Day, you will be guaranteed 5 Sinnoh Stones. See the in-app notification for the date and time of your region’s bonuses.”
It’s worth noting that the two tweets are concluded with different signatures, the first by ^SR and the second by ^KM. These are presumably Niantic staff initial. The fact that two different people came in to make a clarification shows how unclear the information has been.
So if I’m understanding correctly, there are a guaranteed 5 Sinnoh stones AS WELL as the 5 chances to earn one through trainer battle rewards.