Can I roll over my active 401(k) (or other employer-sponsored plan) into Betterment?

Your plan provider likely will not let you roll over a 401(k) while it is still active. This same logic applies to 403(b)s, Pensions and other employer-sponsored retirement plans. For most providers, they require you to be retired or no longer employed at the company to be allowed to roll over retirement funds. Ask your provider to see what their rules are.