The RSS response format will cease functioning when API v1 is retired. On March 5th, you’ll experience a one hour blackout from 9am to 10am PST where the final state of such endpoints can be witnessed in advance of the final cut off.
API v1.1 is JSON-only and requires auth. You should adapt your uses of the RSS feeds to the richer data offered in our JSON representations. If you leverage RSS feeds for display on a website, you should use [node:10248].