GGG has announced that the official 4.0 reveal will be at Exilecon in November, alongside the reveal of the 3.9.0 expansion, and its challenge league. The expectation of the 4.0 launch is that it is at least a year out, and that GGG will be continuing the 13 week cycle for leagues leading up to it.
Exilecon’s keynotes, trailers, and gameplay, both of the 3.9.0 expansion and the 4.0 update will be streamed live, so even if you cannot make it out yourself, it will still be possible for you to keep up with all the excitement.
According to the announcement, both 3.9.0 and 4.0 are going to be gamechangers, in their own way. You can check out the official announcement here