“We are also hoping to release the 2.6.3 patch to the live servers in the next week, which includes the new microtransaction system,” the team added. “We want to get this deployed as soon as we can so that everyone can start using their microtransactions in the beta and be able to test the content in style.”
Considering that the team has said in the past that it wants to get the expansion out this month, that puts the release window somewhere in the last week of July.
Source: Path of Exile