The 3a has a 5.6-inch screen while the 3a XL has a 6-inch screen. Both run on older Snapdragon 670 processors. Launching on all U.S. carriers except AT&T, but can also be bought on the Google Store. 
Available in black, white, and purple-ish. Has a standard 3.5mm audio port.
The Pixel 3a vs. the Pixel 3 and Pixel 2: What's changed? Engadget
YOUTUBE vMwZaKJouSM Google I/O'19 - Soniya Jobanputra Interview on Pixel 3a and Pixel 3a XL