Sigma announced a YouTube stream this coming Wednesday to announce new products. Yes products, as in plural. The 150-600mm FE mount lens has been expected for some time, but apparently there is at least one additional product to introduce next week.
Sigma has been rolling through its lens catalog that was previously designed around the Canon EF mount system, and updating models with new coatings and design techniques around a more flexible, mirrorless-oriented flange distance modeled on the Sony FE system because that system is the more limiting among the mirrorless mounts. This allows the potential for Nikon Z and Canon RF mount adaptations at some future point.