The US Labor Department has taken a neutral stance on allowing companies to include cryptocurrency in 401(k) plans. However, the government supports private equity and annuities as investment options. To invest in bitcoin or other alternative assets through an employer-sponsored plan, several hurdles need to be overcome before this becomes possible.
Source: https://www.marketwatch.com/story/is-all-hell-about-to-break-loose-in-your-401-k-f760af0c