It looks to be soon. Maybe a month? Sorry, you will need to Google translate.
"RAD Studio Berlin 10.1 Update 1 – we are down to the final handful of bugs to address and then will enter testing and acceptance. This has approximately 250 fixes along with several new features."...
From what I've read, the majority consensus seems to be that Seattle is the most stable release so far, but there have been a few instances where XE8 has performed better for some. Either way, hopefully Berlin moves forward rather than backwards.