From May 5th to May 12th Free XP will be sold in Caliber. During this period, an extra shelf will open in the in-game Store in the Boost Progress tab.
In total, five packs will be available throughout the sale, containing from 10 000 up to 500 000 Free XP. The packs will cost from 200 up to 5 000 Coins, respectively. Each item is only available for purchase once per a single account.
The once per account limitation is only applied for the current sale. This means that if you've purchased the Free XP during a similar sale before, you can purchase it again.
You can get Coins in the Store on the website, while the Free XP packs special offers are only available in the in-game Store.