What are my options regarding rolling over an existing 401(k) from a previous job into an SARSEP IRA in my new job?

So recently I got a new job, this company offers SARSEP IRA retirement option account. Currently I have a 401(k) that I’ve had for about 10 years now and I’m trying to figure out what my options are. Can I do a direct rollover of the 401(k) into the SARSEP or do I have to Convert the 401(k) into a traditional IRA and have them separate. I would rather roll them over into one account if that’s an option, but I am getting conflicting information when I do a Google search. I know SARSEP accounts are mostly grandfathered in and are not used as much anymore so I’m just not sure the best course of action here.