Since 4 March 2026 I am seeing "is=" in some YouTube links instead of "si=", also with the 16 character ID.

We set up a bot on r/asmr to reply to anyone posting a YouTube link containing the "si=" parameter, warning that it was likely a tracking ID that Google could potentially use to tie their YouTube account to their Reddit account with some degree of probability and suggesting that they delete their post and re-post without the si= parameter. Many were grateful for the warning and info but some didn't care. We decided to disable the warning after a few weeks.

t= is the only useful parameter in YouTube URLs (that I know of). If not for that we could just strip all of the parameters out.