"M(82589933) was discovered in December 2018. It took more than seven and half years to re-check every smaller Mersenne number to make sure no errors were made during inital testing. This is a very important milestone for the GIMPS project. Many dedicated GIMPS volunteers participated in this effort. The next Mersenne milestone will require a significant effort, please consider joining this important double-checking task."
https://www.mersenne.org/