A Canon Rumors reader has let me know that Amazon jumped the gun on posting the soon-to-be-announced Canon RF 16mm f/2.8 STM
Canon RF 16mm f/2.8 STM Specifications
9 elements in 7 grounds (1 aspherical element)
13cm/5.1″ minimum focusing distance
Maximum magnification of 0.26x
A filter size of 43mm
Lens length of 40.1mm/15.7″
Canon “RF 16mm F2.8 STM” has a lens configuration of 9 elements in 7 groups (1 aspherical lens), a minimum shooting distance of 13 cm, a maximum shooting magnification of 0.26 times, and a filter diameter of 43 mm. It seems that the length will be 40.1 mm.
Update: Here are the first images of the Canon RF 16mm f/2.8 STM.