I got a new bike with a tubeless setup. I’m not sure whether I need to buy sealant to put in or whether it will already have it. Anyone have any experience?

Leaving the bike still for a bit, and then spin the wheel round. If you listen carefully, you should be able to hear the sealant sloshing around.

Doesn’t sound like it. Given the front is also loads softer in the last week, I guess it means no sealant.

If you don’t think it does, just pop off a small part of one side of the tyre wall, and have a peek. I find it is easier to put sealant in this way too (the valve always seems to get clogged for me putting it in that way). If you only unseal a small part of one tyre wall, you should find it is fairly easy to get reinflated.