If you need a refresher, photo and video backups made in high (slightly compressed) or express (compressed to 3MP) quality will begin to count against account storage starting June 1 — that means anything that has already been backed up is safe. Every user has 15GB of free space shared between Photos, Google Drive, and Gmail. If you're bumping on that ceiling, you'll need to pay for a Google One subscription to get more room.
Owners of the earlier Pixel phones have gotten original quality backups for free, but their ranks are slowly shrinking. Pixel 2 devices lost that amenity this past January while the Pixel 3 series will reach the end of the line next January. Those with the original Pixel and Pixel XL are the only ones to keep that perk in perpetuity given their phones' ability to upload all that media. We're not sure we can advise digging through eBay to get your hands on one, though.
The policy change was announced in November. Google is reminding customers this week through emails and a blog post on The Keyword.
