The following is the May 10, 2021 Congressional Research Service In Focus report, Navy Next-Generation Attack Submarine (SSN[X]) Program:
Background and Issues for Congress.
From the report
Introduction and Issue for Congress
The Navy wants to begin procuring a new class of nuclear-powered attack submarine (SSN), called the Next-Generation Attack Submarine or SSN(X), in FY2031. The SSN(X) would be the successor to the Virginia-class SSN design, which the Navy has been procuring since FY1998....
https://news.usni.org/2021/05/11/report-to-congress-on-navy-ssnx-next-generation-attack-submarine