What the upgrade includes
The Deluxe Edition adds three announced items to the standard game: the Ceremonial Armor Set, Axe of the Gods, and a post-launch expansion. Steam sells the Deluxe package and also lists a separate Deluxe Edition Upgrade for players who already own the base game.
The developer announced US launch pricing of $19.99 for Standard, $29.99 for Deluxe, and $10 for the upgrade. Regional pricing and temporary bundles can differ, so compare the live cart totals before buying.
What is not established
The cited launch materials do not provide a release date or complete scope for the post-launch expansion. Buying Deluxe therefore secures the announced entitlement, not a promise that the expansion is already playable in launch build 24852272.
Which edition to choose
Choose Standard if the complete base adventure is the only confirmed content you want today. Choose Deluxe when the named cosmetics/equipment and future expansion are worth the current price difference to you. Existing Standard owners do not need to repurchase the base game; the separate upgrade is the relevant comparison.