I just checked for a quick sample from IRC and got this (some values removed):
@badge-info=;badges=;color=;display-name=;emotes=;flags=;id=;login=;mod=;msg-id=viewermilestone;msg-param-category=watch-streak;msg-param-copoReward=450;msg-param-id=STREAKID;msg-param-value=10;room-id=;subscriber=1;system-msg=USER\swatched\s10\sconsecutive\sstreams\sand\ssparked\sa\swatch\sstreak!;tmi-sent-ts=;user-id=;user-type=;vip=0 :tmi.twitch.tv USERNOTICE #CHANNEL :MESSAGE
It appears to be the same as from 2023 when they first started testing Watch Streaks.