The last stable official builds (often in the 14.x or 15.x range) that still communicate with Google’s servers without forced update prompts. Modified Clients:

You cannot install a custom APK over the old factory version.

Compatibility with Android 4.4.2 (KitKat)

This is a known bug on KitKat. The legacy WebView renderer crashes on some comment threads. The better alternative is to use YouTube 14.21.54 , which uses an older comment rendering system that is more stable.