Twitch Theater Mode for YouTube is a Chrome add-on developed by Splinterman. This free tool aims to change the YouTube theater mode to resemble Twitch theater mode when chat is enabled.

When using Twitch Theater Mode for YouTube (TTM), the main video view expands, and the chat box is moved to the right-hand side of the screen. In addition, all other on-screen elements are hidden, providing a cleaner and more immersive viewing experience. It's worth noting that these changes revert back to the default YouTube layout once theater mode is exited.

However, it's important to mention that as of August 22, 2023, the YouTube web player has been undergoing multiple updates, which has caused some compatibility issues with the extension. The developer, Splinterman, plans to react to these updates as soon as possible until YouTube stabilizes.

In the latest version, v4.02, a new feature has been added, allowing users to hide or show the chat box according to their preference. This gives users more control over their viewing experience.

Overall, Twitch Theater Mode for YouTube provides a convenient way for users to enjoy a theater-like viewing experience on YouTube, especially for those who are accustomed to Twitch's theater mode. However, due to recent compatibility issues with YouTube updates, users may experience occasional disruptions in functionality.