Reddit plans to introduce a login requirement that will restrict access to much of its website and app for users who aren’t signed in.

For more than two decades, Reddit has allowed people to browse most of its content without creating an account. However, chief executive Steve Huffman says the company intends to move towards a primarily logged-in experience, arguing that the change will improve personalization, strengthen its advertising business, and protect user data.

Visitors who are logged out will still be able to access certain parts of the platform, including the front page and some content reached through search engines or shared links. However, the amount of material available without an account is expected to decrease.…