A trust is not an individual. Only a 401(k) beneficiary that is an individual is permitted to roll the inherited 401(k) over to an inherited IRA, so if left to a trust the inherited 401(k) is not permitted to be rolled over to an inherited IRA and either the entire 401(k) must be distributed to the trust in a lump sum to be includible in income in a single tax year or the inherited 401(k) will need to be maintained by the plan (if they permit) to allow RMDs and other amounts to be paid out to the trust over more than one year. Many 401(k) plans do not permit the inherited 401(k) to be maintained and instead require a lump-sum distribution if the beneficiary is not an individual, so check the plan agreement.
Unless the intent is to protect this asset with a trust, it's almost always a really bad idea to make a trust the beneficiary of a 401(k) due to undesirable tax consequences.
