Update Post 09/22/2021
If you have the 18-month receipt notice that has expired but have yet to receive the new 24-month receipt notice, you may continue to work in light of the 09/03/2021 announcement extending the time that I-751 or I-829 receipt notices can be used to show evidence of lawful permanent resident status.
The expired 18-month receipt notice can be used as list B identity document and a list C document on I-90 when verifying work eligibility.
Existing employees with pending applications to remove conditions should not be terminated for failing to present a new green card once the 18-month extension period expires.
If I-751/I-829 continues to be pending beyond 24 months, you may obtain an info pass appointment at the USCIS field office and get an I-551 stamp on your passport for an additional extension period. See: Get a I-551 Stamp in Passport if your I-751 is pending longer than 18 months
Original Post 09/03/2021
Starting September 4, 2021, Conditional Permanent Residents will get 24 months (an increase from 18 months) of automatic extension while a properly filed I-751 is pending.
Upon the timely filing of Form I-751 or Form I-829, Conditional Permanent Residents will receive a receipt notice that can be presented with their Form I-551, Permanent Resident Card (also known as a Green Card), as evidence of continued status for up to 24 months past the expiration date on their Green Card, while their case remains pending with USCIS.
This also means that even more applicants who file for naturalization after filing I-751 may get naturalized before I-751 is adjudicated.