I would guess that they do it similarly to private trackers. Each user gets a unique and secret ID which is transmitted when announcing. The tracker then decides if the user is allowed to get the swarm details.

Yup. I suspect it's exactly this, branded and hosted by Bittorrent Inc as a paid product.

Does that have the same benefits in terms of distributing the sources?

I just purchased the new Thom Yorke album [0] via a bundle and it felt like a regular torrent. Very quick to download etc.

[0] https://bundles.bittorrent.com/bundles/d0b4beba8efc4b46f6dba...

See what kind of announce URL is included in the .torrent. Is it just

    udp://tracker.publicbt.com:80/announce

or does it include information that could be used to identify you, like

    http://tracker.bittorrentbundle.net:3000/3pr4s5y7l9nh0mdwcqyh3a9k6n7d0kta/announce

Other than tracker identifying you, seeding and downloading works the same in both cases.

Just anyone else is wondering, it's:

    http://tracker.bundles.bittorrent.com/tracker/{a whole lot of hex}

lawyers.

regardless of how they configure their trackers, this only works if people dont use clients that use others trackers

I'm not sure why you're downvoted, technically you are (probably?) correct.

If they use technology similar to private trackers, that won't help against peer exchange.

And yes I think other trackers could announce the same torrent and have people join the same swarm.

I could not imagine what else they'd do.

It appears that Thom Yorke's new album has been released using this feature:

https://bundles.bittorrent.com/bundles/d0b4beba8efc4b46f6dba...

Yes that was why I asked. I did not know about Bundles or private tracker before downloading this album.

Strangely enough, I downloaded Thom York's album yesterday from Bittorrent Bundle, and this morning my torrent is displaying an error: "Tracker gave HTTP response code 402 (Payment required)".

So I guess it's not very torrent friendly, as I cannot seed any more.

Yeah I am getting also a 402 response from the tracker. I wish they would have put up a BEP or something with an explanation of how they're extending the tracker protocol...