I wrote an application that uses YouTube Data API V3's search.list, which was able to pull active live streams for a specified channel (working since 2018) using the following:
https://www.googleapis.com/youtube/v3/search?part=snippet&channelId=UCSJ4gkVC6NrvII8umztf0Ow&type=video&eventType=live&key={MYAPIKEY}The above no longer returns any results for me as of September 12, 2019.
Broadening the search to all videos for a specified channel also no longer shows the active live stream:
https://www.googleapis.com/youtube/v3/search?part=snippet&channelId=UCSJ4gkVC6NrvII8umztf0Ow&order=date&key={MYAPIKEY}However, searching the ID of the active live stream itself works to return information about the video, which leads me to believe there may still be a way to accomplish this:
https://www.googleapis.com/youtube/v3/videos?part=snippet&id=hHW1oY26kxQ&key=I am looking for a new solution that would be able to query a channel to see if they have an active live stream running, and grab the properties for that live stream.