In Android Q beta 4, making the same gesture seen in the GIF would open the Assistant, but there was no flashy animation to let the user know that his gesture was accepted. Instead, haptic feedback gave the user confirmation that Google Assistant was about to awaken.
The gesture that opens Google Assistant appears to be a diagonal swipe up from the lower left of the display to the upper right corner. Two lines of rainbow-colored lines appear on the bottom of the screen, broken up with a space in the middle. That is quickly followed by the Google Assistant stub that opens on the bottom of the display.