You do have to agree to certain terms (you agree to receive promotional emails from OneDrive in exchange for that, but it’s possible to unsubscribe from those at any time).

If you’re interested, here’s an article in gHacks about the offer: LINK.

Source:

http://www.ghacks.net/2015/02/10/get-100gb-onedrive-space-for-2-years-bing-rewards-us-only/?_m=3n%2e0038%2e1515%2ehj0ao01hy5%2e1kii