are disc brakes ready bled?

When you buy a new brake does it come ready bled?

Depends on the make, and not even that. Both a friend and I recently bought XT discs from merlin. His came bled, I had to assemble, then bleed, then rebleed, then eventually take them humbly to the LBS to get to work as the pistons wouldn’t unstick. Ask before you buy…

Be prepared to bleed them anyway. I have never had to bleed Hope brakes for spongyness reasons, but often had to re-route hoses so needed to bleed.
The last bike I put brakes on I used OEM XTs and they had more air in them than fluid. After bleeding they were awesome though.
If they are Avid or Hayes you’ll need a bleed kit (they need threaded fittings), most others you can do with a length of tubing and a Fairy liquid bottle.