Backwards Compatible Permalinks

Backwards Compatible Permalinks helps prevent 404 errors when switching between permalink structures.

It achieves this by appending a set of backwards compatible post rewrite rules. This ensures posts are still accessible at their previous permalink after the permalink structure is updated.

Example

Let’s say your permalink structure is set to “Month and name” and you have a post titled “I Love WordPress.” That particular post would live at https://example.com/2019/03/i-love-wordpress/.

But what if you wanted to switch to the “Post name” permalink structure and have your post live at https://example.com/i-love-wordpress/ instead?

You could but this would result in the existing post permalink 404ing when visited. Which is problematic if the previous…