Baldur's Gate 3 studio Larian Studios says it would be kind of dumb for players to dive too deep into the current Early Access release. The studio says that no progress from the Early Access release will carry over to the full game when it launches on August 3rd. They instead say to look at a purchase of the Early Access release as "essentially a pre-order."
Not only will all progress be wiped, but a lot of the content present in the available Early Access build is "out of date." Because of how old and outdated a lot of the content is in the Early Access build, it would not be easily possible to make the save files compatible with the full release build.
(...)We’re recommending that players don’t buy the Early Access version of Baldur's Gate 3 with a view to play through that content, partly because it’s out of date but mostly because we’re so close to launch and want to make it very clear that saves in the Early Access version will not transfer into the final game. This is due to technical reasons.
Essentially, the game is so vastly different that it’s not possible to make those save files compatible. Early Access will, of course, remain playable up to launch.
A purchase of Early Access is essentially a pre-order, and will still grant you access to the Digital Deluxe content for Baldur's Gate 3 on PC, granting you access to: an exclusive in-game dice skin, the Divinity Bard Song Pack, Treasures of Rivellon Pack, Adventurer’s Pouch, Digital OST, Digital Artbook, and Digital Character Sheets for D&D IRL.​
Essentially, the game is so vastly different that it’s not possible to make those save files compatible. Early Access will, of course, remain playable up to launch.
A purchase of Early Access is essentially a pre-order, and will still grant you access to the Digital Deluxe content for Baldur's Gate 3 on PC, granting you access to: an exclusive in-game dice skin, the Divinity Bard Song Pack, Treasures of Rivellon Pack, Adventurer’s Pouch, Digital OST, Digital Artbook, and Digital Character Sheets for D&D IRL.​
The PC Digital Deluxe Edition does not include a 72 hour head start, which would have essentially made the game’s release date July 31st. Shifting the release date – and thus communication around the Digital Deluxe Editions across PS5 and PC – came with a few complexities that we didn’t manage to communicate very well, so we thought it best to clarify it here, given that a 72 hour head start on PC wouldn't have been plausible.
