Back in 2020 we moved all sites from being served under *.netlify.com to being under *.netlify.app. This was to isolate customer sites from ones run by Netlify, trying to minimize the confusion. In doing this, we built in an automatic redirect for subdomain.netlify.com to subdomain.netlify.app to avoid downtime on customer sites. Now most sites either use the .app url directly, or have a custom domain.
Starting on Friday March 29th, 2024, new sites won’t be getting this behavior as we begin phasing it out. This means that your older sites will continue redirect from *.netlify.com to *.netlify.app, but new sites will not. Our plan is to fully deprecate the feature by the end of April.
What this means for you is really, nothing much! If you’ve got a site that is accessible by subdomain.netlify.app, it will continue to be fully reachable. If your link is to subdomain.netlify.com, it will stop redirecting in May. You’ll need to use the .app url.
If you’re using a CNAME linked to subdomain.netlify.com, generally, you’ll wanna update that to be for your .app domain, but it will continue to work for DNS.
If you’re running into problems with this, please post in this thread or contact support for help.