In my experience they are a combination of both. You start a chat with a computer who notifies a 'real person' - sometimes it's out of hours and the person doesn't get back to you til the next day (I hate that, don't pop up with a LIVE chat request if there is no one there) but if it's during office hours I've only had to wait a few minutes to be chatting with a human
Especially when you get the preliminaries over quickly like: "My name is qak and I need help with X" and the robot reply is "Who am I chatting with today" (wait for reply) and then "How can I help you today?" (waits for reply).
nb IKEA's Anna is totally computerised, she doesn't want to know who you are!