This is the first point of the Octane FAQs:
https://home.otoy.com/render/octane-render/faqs/To sum up Octane 3 runs on any card with compute capability 2.0 or above, on the other hand Octane 4 requires 3.0 or above (Fermi support has been dropped, check the release notes for more info) so you should be good in both cases.
You can check the relation of GPU models and their respective compute capabilities here:
https://en.wikipedia.org/wiki/CUDA#GPUs_supportedI hope that helps.