By default, Foundry uses a Load Balancer behind a set of Public IPs to egress to the Internet. You can find the set of egress IPs corresponding to your Foundry instance in Control Panel under Network Egress → Network Policies tab, by expanding the “What IPs do connections from Foundry come from?” pane. Those IPs won’t change without prior notice.
You can find out more about configuring network egress in the documentation.