Fidelity Investments plans to allow investors to put a bitcoin account in their 401(k)s, the first major retirement-plan provider to do so.

Employees won't be able to start adding cryptocurrencies to their nest eggs right away, but later this year, the 23,000 companies that use Fidelity to administer their retirement plans will have the option to put bitcoin on the menu. The endorsement of the nation's largest retirement-plan provider suggests crypto investing is moving further into the mainstream, but it remains to be seen whether employers will embrace it for their workers.