RockShox Reverb AXS (1st generation) is offered in several seat tube diameters with varying travel to accommodate different seat tube lengths:
Diameter: 30.9, 31.6, 34.9mm
Travel: 100, 125, 150, 170mm
Check out our Reverb AXS sizing guide, found on the SRAM Service Site, to help choose the right size for you.