The activation of the Bellatrix upgrade on the Ethereum blockchain triggers the beginning of the Merge, which will likely be completed sometime around Sept. 13-16. The Terminal Total Difficulty (TTD) value triggering the Merge has been set at 58,750,000,000,000,000,000,000. This number, which will represent the cumulative difficulty of all mined Ethereum blocks, is expected to be reached somewhere between Sept. 13-16. It’s predicted that it will happen around Sept. 15.