Event types: every change it reports

The events

Badge	Feed filter	Type	What it means
New video	Uploads	`new_video`	A new upload appeared on a tracked channel. It is found by the uploads-tab sweep or by YouTube’s public Atom feed, whichever sees it first.
Title changed	Title changes	`title_changed`	Every observation agreed on a title that differs from the last one recorded, so the creator changed it. A title that returns to one shown recently is recorded as an A/B test instead.
Thumbnail changed	Thumbnails	`thumbnail_changed`	Every observation agreed on a different thumbnail. Thumbnails are compared as pictures (perceptual hash distance of 6 or less is the same image), so a re-encode is not a change.
A/B test	A/B tests	`ab_test_detected`	Viewers were shown different titles or thumbnails for the same video within the same short window: independent identities disagreed within one probe cycle, or the uploads tab alternated between versions it had already shown.
Breakout	Breakouts	`breakout`	An upload between 8 and 72 hours old is gaining views at least 3× as fast as the channel’s own uploads did at the same age, and already was 6 hours earlier. It needs at least 1,000 views.
Milestone	Milestones	`milestone`	A channel’s public subscriber count crossed a round number (10K, 25K, 50K, 100K and so on up to 100M). It is dated at the crossing, not at the moment it was noticed.
Removed	Removed	`video_removed`	Every identity in one probe cycle was told the video is unavailable. It is reported once, and the video is no longer probed.
Members-only	Members-only	`members_only_changed`	A video switched between members-only and open to everyone. Only a switch between two observed states is reported.
Renamed	Renames	`channel_renamed`	The channel’s name or handle changed, confirmed by two agreeing observations in a row.
New avatar	Avatars	`channel_avatar_changed`	The channel’s avatar changed, confirmed by two agreeing observations and compared as a picture, so YouTube re-encoding the same image is not reported.
A/B result	A/B results	`ab_test_concluded`	An A/B test has not been seen for 72 hours and the video’s current title or thumbnail matches one of the tested versions. That version is reported as the one that stayed. Reported once per test.

How the feed groups them

When a channel is first tracked, the uploads already on its page arrive together and are grouped into one card.
One A/B test is one card, however many times it was seen. Its sightings are joined into a single run.
The first switch of a title or thumbnail that turns out to be an A/B test is shown as part of the test, not as a separate change.
A test's result is its own card, separate from the test, because it is separate news: the test settled.

Where each event comes from

Sweeps read a channel's uploads tab and its header. They produce uploads, title and thumbnail changes, A/B tests that show up as alternation, renames and avatar changes.
Probes load a recent video's watch page from several independent identities, one after another within one probe cycle. They produce A/B tests, removals and members-only switches. See how detection works.
The Atom feed discovers uploads and their exact publish time. It never produces any other event.
Breakouts, milestones and results are computed from what the sweeps and probes already recorded.

The events

Badge	Feed filter	Type	What it means
New video	Uploads	`new_video`	A new upload appeared on a tracked channel. It is found by the uploads-tab sweep or by YouTube’s public Atom feed, whichever sees it first.
Title changed	Title changes	`title_changed`	Every observation agreed on a title that differs from the last one recorded, so the creator changed it. A title that returns to one shown recently is recorded as an A/B test instead.
Thumbnail changed	Thumbnails	`thumbnail_changed`	Every observation agreed on a different thumbnail. Thumbnails are compared as pictures (perceptual hash distance of 6 or less is the same image), so a re-encode is not a change.
A/B test	A/B tests	`ab_test_detected`	Viewers were shown different titles or thumbnails for the same video within the same short window: independent identities disagreed within one probe cycle, or the uploads tab alternated between versions it had already shown.
Breakout	Breakouts	`breakout`	An upload between 8 and 72 hours old is gaining views at least 3× as fast as the channel’s own uploads did at the same age, and already was 6 hours earlier. It needs at least 1,000 views.
Milestone	Milestones	`milestone`	A channel’s public subscriber count crossed a round number (10K, 25K, 50K, 100K and so on up to 100M). It is dated at the crossing, not at the moment it was noticed.
Removed	Removed	`video_removed`	Every identity in one probe cycle was told the video is unavailable. It is reported once, and the video is no longer probed.
Members-only	Members-only	`members_only_changed`	A video switched between members-only and open to everyone. Only a switch between two observed states is reported.
Renamed	Renames	`channel_renamed`	The channel’s name or handle changed, confirmed by two agreeing observations in a row.
New avatar	Avatars	`channel_avatar_changed`	The channel’s avatar changed, confirmed by two agreeing observations and compared as a picture, so YouTube re-encoding the same image is not reported.
A/B result	A/B results	`ab_test_concluded`	An A/B test has not been seen for 72 hours and the video’s current title or thumbnail matches one of the tested versions. That version is reported as the one that stayed. Reported once per test.

How the feed groups them

When a channel is first tracked, the uploads already on its page arrive together and are grouped into one card.

One A/B test is one card, however many times it was seen. Its sightings are joined into a single run.

The first switch of a title or thumbnail that turns out to be an A/B test is shown as part of the test, not as a separate change.

A test's result is its own card, separate from the test, because it is separate news: the test settled.

Where each event comes from

Sweeps read a channel's uploads tab and its header. They produce uploads, title and thumbnail changes, A/B tests that show up as alternation, renames and avatar changes.

Probes load a recent video's watch page from several independent identities, one after another within one probe cycle. They produce A/B tests, removals and members-only switches. See how detection works.

The Atom feed discovers uploads and their exact publish time. It never produces any other event.

Breakouts, milestones and results are computed from what the sweeps and probes already recorded.