It’s running through February 28, 2023
Pokemon Scarlet and Violet aren’t scheduled to arrive until November 18, but a special Pikachu distribution event is already a go.
https://www.youtube.com/watch?v=mZf-vIpVDLo
Sneakily announced at the end of a trailer that debuted during the August 2022 Pokemon Presents stream, the event kicks off roughly around when the game starts. It’s for a “special Pikachu,” and will be in line with the new “Terastallizing” form mechanic that’s been introduced in this generation.
It knows the move “Fly,” and is also a flying Tera type. The event will run from the game’s launch (when you can access it), through February 28, 2023. It’s similar to other early access events from mainline games: the idea is to incentivize players into picking up the game early. That’s pretty much all we have in terms of details at the moment.
As for the technical fine print, The Pokemon Company notes that you can acquire this through normal mystery gift means — which also confirms the feature for Scarlet and Violet (as if there was any chance it wasn’t coming back). You do not need a paid Switch Online membership to access the special Pikachu distribution event, and it takes “one to one and a half hours” to work up to the point where the mystery gift feature is enabled.