回複：回複：回複：回複：回複：To xiaobaitu or other experts

AC21 is called portability provisions of the American Competitiveness in the Twenty-first Century Act for Adjustment of Status applicants. Essentially it allows for approval of employment-based adjustment of status applications through an employment offer other than the one contained in the LC and I-140, provides certain requirements are met: a. the I-485 must be pending for at least 180 days; b. the new job must be the same as, or silimar to, the job described in the LC and I-140.

AC21 doesn't state that notification to USCIS is required when one invokes AC21. However, the current guidance on the issue says that it is "expected" that a letter will be sent to USCIS. You better consult an immigration lawyer on this.

Good luck.