Update - The final cut over has been changed to March 6th, 2019 starting at 9:00am PT, Authorize.Net will be disabling the old IP addresses for our API endpoints and only the new IP addresses will function.

For more details, see our support article, Authorize.Net Domains and IP Addresses:
https://support.authorize.net/s/article/Authorize-Net-Domains-and-IP-Addresses
Jan 28, 15:52 PST

Scheduled - We are upgrading the way we manage our network infrastructure to be more responsive to events and business need. In order to support these changes, we are changing the IP addresses used by our API endpoints. The URLs and domains for all Authorize.Net websites and services will remain the same.

On February 13th, 2019 starting at 9:00am PT, Authorize.Net will be disabling the old IP addresses for our API endpoints and only the new IP addresses will function.

For more details, see our support article, Authorize.Net Domains and IP Addresses:
https://support.authorize.net/s/article/Authorize-Net-Domains-and-IP-Addresses
Dec 7, 14:53 PST