According to the IRS, starting on January 1, 2021, all new hires must use the new 2021 W-4, and any employees hired prior to 2021 who want to adjust their withholding must do so using the new 2021 W-4.
Existing employees who have submitted Form W-4 before 2021 are not required to submit a new form merely because of a new version being released. Employers will continue to compute withholding based on the information from the employee’s most recently submitted Form W-4.
As in previous years, existing employees who have filed as "EXEMPT" status and are looking to carry that status into the new year will need to submit a fresh W-4 to do so.
For more information regarding the W-4, please visit IRS.gov.
Also see: How to complete a W-4 in TiM