Gen 3 Prius coolant heater
 

I was under a 2010 prius last week, it had these coolant hoses going to the cat converter, it had a valve on it too. Is this setup for quick warm ups or emissions? I'd guess its both.

Its not actually a cat, the cat is before the coolant heater. But, yes its for emissions and quicker warm up and sustaining the engine temperature with lots of engine off use.

Yeah, I think there was a cat infront it.