This is actually just part of stock Android. My Pixel 5 has MAC randomization on by default for new Wi-Fi networks.
It’s per-network, not per-connection. Though that option does exist but is hidden away under developer settings.
It’s not at the packet level - by default on gOS (and a dev option on stock pixels), every time you connect to a network, even ones you have connected to prior, you get a new random MAC. The standard aosp/pixels do one random but persistent MAC randomization. This only helps marginally from a privacy standpoint. Per-connection makes this data point useless, thereby increasing privacy.