USCIS provided the following updates on the new Form I-539:
- An official copy of the revised Form I-539 and new form I-539A will be published on the USCIS website on March 8, 2019.
- USCIS will continue accepting Form I-539 with an edition date of 12/23/16 until March 21, 2019, as long as it is received by USCIS by that date.
- USCIS will reject any Form I-539 with an edition date of 12/23/16 that is received by USCIS after March 21, 2019.
- Starting on March 22, 2019, USCIS will only accept the revised Form I-539 with an edition date of 02/04/19.
This information is currently posted on the I-539 page of the USCIS website.