1. Install OBS
2. Download a zip file of this repository from the Releases section on the right side of the page
3. Extract the downloaded zip file
4. Follow the steps below for the CSS theme and the script

1. In the extracted zip file, right click on youtube-live-qa.css and select Edit
2. Select all and copy the CSS
3. In OBS, create a new Browser source
4. Set it up with the following recommended defaults:
   • Name: Live Q&A
   • URL: https://www.youtube.com/live_chat?is_popout=1&dark_theme=1&v=jfKfPfyJRdk
     • Set the video ID to the ID of your livestream, you can use the Script below to update this value later
   • Width: 1000
   • Height: 500
   • Custom CSS: Paste from youtube-live-qa.css

Until you start the Q&A session, the source will be entirely invisible. (Keep in mind that pinned messages might be visible, so it's best to hide the source when not using Live Q&A.)

Advanced usage: You can customise the font and appearance by manually editing the CSS or combining it with Chat v2.0 Style Generator.

You can see the CSS theme in action in this video (keep in mind that this was an early test without theming support and with unwanted expand-collapse animations.)

1. Download and instal the latest version of Python 3.10 from python.org
2. In OBS studio, click on Tools → Scripts
3. Navigate to Python settings
4. Click on Browse
5. For the Folder, copy and paste exactly %localappdata%\Programs\Python\Python310 (if you used the defaults while installing Python)
6. Click on Select folder
   • you should see Loaded Python Version 3.10 in OBS
7. Navigate to Scripts
8. Click on the + to add a new script
9. Navigate to where you extracted the zip file and select update-youtube-chat-url.py
10. Select the newly added script update-youtube-chat-url.py
11. Paste in your stream URL
    • This URL is only generated once you start streaming, so you can fill it in later
    • Hover over the (?) to see what URLs are supported
12. Click on Update sources to update all YouTube chat browser sources (the button is disabled if the URL is invalid)
    • When you use Update sources, all YouTube chat Browser sources will conveniently update to the new URL (even if they're displaying regular chat and not Live Q&A)

1. In OBS studio, click on Tools → Scripts
2. Select the script update-youtube-chat-url.py
3. Paste in your stream URL
4. Click on Update sources

Doesn't properly work when there is a pinned message in chat. Unpin all messages before starting a Live Q&A session for best results.

Thanks to @VocaCircus for the idea and for trying it out!