Despite the recent launch and release of the OnePlus 5T, the next flagship, the OnePlus 6, will most likely arrive on March 2018.
This new information points to a phone announcement in mid-March, and an official launch at the end of the month. However, the even bigger news here involves the under-glass fingerprint sensor that will supposedly come with the OnePlus 6. If OnePlus times this correctly, they may become the first brand to introduce the sensor on the display.
For any specs or build news, though, you may want to wait a few more weeks for anything major.