Sumopayroll is primarily a Saas solution which means we are cloud only.
We do not encourage customers to go the route of an on-prem solution due to various reasons like frequent updates to the product, tax code changes at the beginning of the fiscal year among other reasons.
However, we do offer a custom solution to customers that really wanted to host it themselves. The minimum requirement for such an on-prem solution is that you have a minimum of 1000 employees and the standard pricing on our website is not valid for on-prem customers.