Based on testing from a few years ago, 90 channels was about the upper practical limit for a single connection. Too many more channels than that and the connection would eventually be disconnected.
Caveats
- Testing was done only in the top channels on Twitch (which was updated about every 30 seconds to ensure they were the absolute top channels at that moment), likely representing the top percentile of chat activity (among active live channels).
- The testing was done a few years ago and has not been repeated since.
- I do not know if there were any special events or mass spamming campaigns at the time.
- I only still have the conclusions from the testing, not the actual data (e.g., what channels, how many active chatters, peak bandwidth or message rate).
You can’t predict what chat activity will look like over the next few milliseconds with complete accuracy, so I err on the side of extreme caution.