Google Waymo’s autonomous cars have driven 6.4 million km on public roads

But it's not just the milestone the company is celebrating, it's the pace: While it took the company 18 months to reach 1 million, then 14 to reach 2 million, then 8 months to reach 3 million and finally six months to reach the 4 million mile marker.

While these have been on public roads, they've been restricted to cities in California's Bay Area and around Phoenix, Arizona, with some testing in Austin, Texas and Kirkland, Washington. Waymo had been refining its autonomous tech in partnership with Lyft, though it's unclear how much influence that has had.

In addition to real driving, the company has put its systems through 2.5 billion simulated miles in the last year, Waymo's blog post boasted. With all that experience, the company says its been able to teach its vehicles enough to pull off "full autonomy," and hinted that the public would soon "get to use Waymo's driverless service to go to work, to school, to the grocery store and more."