Been married for 5 years, can spouse get half of 401K

The answer depends upon when contributions began and ended and whether in your state post-separation earnings (and therefore contributions to the 401(k)) are separate property (as in California).

Since pre-marital and post-separation contributions in California are separate property, those are out of the equation in dividing the 401(k). The marital contributions (in CA defined as date of marriage to date of separation) plus the gains and losses attributable thereto are community property and divided equally.

Much of the time the division is not 50-50 but again, it depends on the issues I mentioned.