At least in the US, the red light/stop sign braking happens whenever AP is operating just under cruise control or under autosteer.
Note this is still an early release of this functionality - so drivers shouldn't rely on the software to operate correctly. It will stop at a light, even if it is green, unless there is a vehicle directly in front of you driving through the intersection when the light is green. The software is being very conservative right now - slowing down and stopping and requiring the driver to confirm it's OK to proceed through the intersection.
And that's OK - for now...