The carrier Three Ireland confirmed in its pre-order page that pre-orders will open on October 4 and that early orders (before October 11) will be delivered on October 12:

The Google Pixel 8 Series will be available to pre-order from 4th October 2023.

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If you pre-order either the Google Pixel 8 or Google Pixel 8 Pro before 11th October at 3PM, your new phone will be delivered by 12th October. Subject to courier lead time.

Photos also emerged showing a matte glass back for the Pixel 8 Pro:

front back