At what difficulty will XPM block be halved?

Current difficulty is 7.97, and block dropped to less than 16 in merely a week. Looks like we don’t have to wait 4 years for XPM to halve.

What did the blocks start at? I only got in on day 4.

Reward = 999/(diff^2). Reward started around 20 at diff = 7, so it will halve at diff = 10.