Every year, it seems, that Google has trouble with keeping their smartphones in stock. It was something that was very popular with the Nexus smartphones (anyone remember trying to order a Nexus 4 when it went on sale?) and it appears to be carrying over to the new Pixel lineup. Although it did take a few days for these devices to sell out, but the Pixel XL does appear to be completely sold out in all colors and storage sizes right now, on the Google Play Store. It's not a huge surprise, given the fact that the Pixel XL is the larger smartphone, and it has been proven that the majority of users want larger smartphones over smaller ones.
As far as the standard Pixel goes, that one is still available, but only in 32GB of storage. The 128GB model is sold out in all three colors. The Really Blue color is also sold out, in both the 32GB and 128GB models. The Very Silver 32GB model is showing delayed shipping of about 5-6 weeks, and the Quite Black 32GB is still in stock, for now. So it appears that the Pixel and Pixel XL are going fast, and this shouldn't be a surprise at all.
Now Google isn't the only one selling the Pixel and Pixel XL, Verizon and Best Buy still have them available for pre-order, however the ones at Best Buy are reportedly the Verizon variants. It's unclear right now if those are completely locked down to Verizon (complete with locked bootloader) or not. They shouldn't be, since the Verizon models sold by Verizon are unlocked and will work on other networks, they just sport a locked bootloader. Best Buy does have the two devices a bit cheaper right now, and offering a $100 gift card as well as a free Chromecast. Definitely making the Pixel or Pixel XL purchase from Best Buy a good looking deal.
The Pixel and Pixel XL are slated to ship on October 20th. So for the majority of those that got their pre-orders in, you should be seeing your device in just a couple of weeks. Those that haven't gotten in their order yet, it may be a while, but Google will be restocking, so don't worry.