They recommend 16×9, 4×3, and 1×1 ratios, Articles are recommended to have a total resolution of 300k pixels while other types 50k pixels.
Articles still have a recommended width of 696px (which is an amp requirement and I assume only for the 16×9 ratio). Events have a recommended width of 1920px and minimum 720px
|Article||550 x 550||630 x 475||730 x 410|
|Others||223 x 223||258 x 193||298 x 167|