Noone can gurantee any specific uptime. Any projection for the future, however qualified and propable, is still only a projection. GMail could go down tomorrow, for 24 hours or forever. (Not, of course, that such optimism is in way warranted).
Whoever downvoted the comment above start your own server, and we'll talk a decade later. The comment is correct; nobody can guarantee uptime. The can promise, there can be agreements, insurance, etc, but guaranteeing is basically impossible. Even if someone were to use a real mainframe cluster across the globe one still connects to them via international ISPs and those routes can go down as well.