Canon announced the development of the RF 1.4x and RF 2.0x teleconverters alongside the EOS R5 a few months ago and will be officially announced on Thursday.
Canon RF 1.4x teleconverter specifications:
7 elements in 4 groups
Size: 71.2mm x 20.3mm (mounted) 40.7mm (total length)
Canon RF 2.0x teleconverter specifications:
9 elements in 5 groups
Size: 71.2mm x 39.3mm (mounted) 60.6mm (total length)
Each of these teleconverters will be compatible with the RF 100-500mm f/4-7.1L IS USM, RF 600mm f/11 IS STM and RF 800mm f/11 IS STM.