I use OpenWRT on 2/3 of my home routers but the 3rd I have no idea which version I should be using. Or if it's even supported. I can't find any mention of it in the device search facility.
The C2600 is there. But no AC2600. Apparently, it uses a Mediatek 7615N chip.
Embedded devices, such as routers, aren't like x86_64 systems, where an OS would boot on basically any computer - they will need a dedicated image for each single model. The good part is that the hardware specifications of your router suggest that it should be possible to support it, the bad part - if it isn't explicitly marked as support in the ToH, then it isn't supported (hint, it's not listed) and will need porting by someone with this specific device on their desk (which may be you).