According to the IRS, starting on January 1, 2020, all new hires must use the new 2020 W-4, and any employees hired prior to 2020 who want to adjust their withholding must do so using the new 2020 W-4.
Existing employees who have submitted Form W-4 before 2020 are not required to submit a new form merely because of the redesign. 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 2020 will need to submit a 2020 W-4 to do so.
For more information regarding the 2020 W-4, please visit IRS.gov.
Also see: How to complete a 2020 W-4 in TiM