On 5 July 2023, 17:48:23 UTC, PrimeGrid's 321 Prime Search found the Mega Prime:
The prime is 6,300,184 digits long and will enter Chris Caldwell's “The Largest Known Primes Database” ranked 19th overall. This is the largest known prime for the 3*2^n-1 form.
The discovery was made by Arno Lehmann (Zyfdnug) of Germany using an AMD Ryzen 9 7900X @ 4.7GHz with 64GB RAM, running Debian GNU/Linux 12 (bookworm). This CPU took about 6 hours, 20 minutes to complete the probable prime (PRP) test using LLR2.
The PRP was confirmed prime on 5 July 2023 by an AMD Ryzen 9 5950X @ 3.4GHz, running Linux Mint. This computer took about 2 hours, 46 minutes to complete the primality test using LLR2.
For more details, please see the official announcement.