Just As usual, the update log on the phone doesn't really actually mention new changes beyond just claiming to fix existing bugs and improve stability and performance.
For Pixel 3a and the Pixel 3a XL devices this is the first update ever on them. which were released a month ago. The phone where shipped with March 5 security patch even though it shipped in May. It then skipped both April and May patches and directly jumped to June.
For Pixel 3 which is the most expensive of the Pixel , meanwhile, was already on the May 5 security patch so it didn't have to make as big a jump. Still, despite the date of the patch, the Pixel 3 got the update rather late in the month of May.
Looking at many thing, this may not seem of big a deal to some people but timely updates is one of the key selling points of purchasing an Android phone directly from Google because you are always ahead as far security and venerability is concern.
This is also not the first time that Google has skipped couple of months worth of updates (the exact same thing happened when the Pixel 3 launched last year). If we can't expect even Google to stay on top of the update situation, how can we expect it from the other Android OEMs?
Anyway, the updates are now out and you can head to the System update menu on your phone to force it to download the update if you haven't received a notification for it.