As reported in IGN.
After 20 years at Dark Horse, their license for Buffy expires this year (with, I believe, their last issue of a Buffy series shipping this week), and starts at BOOM! Studios in 2019.
Here is the first promo image BOOM! It is not clear yet whether they are continuing the TV canon, as Dark Horse had been doing since 2011. But given that the promo image is about high school, I would guess not.