So they are announcing variable data rate streams and Display Stream Compression support. I thought until now HDMI had a fixed data rate except for the control

So they are announcing variable data rate streams and Display Stream Compression support. I thought until now HDMI had a fixed data rate except for the control channel, unlike DisplayPort which is fully packetized. Can someone more knowledgeable chime in on whether HDMI will now be packetized too, or how they support variable data rate modes?