Run File > Collect All and Save before you copy, zip or send a Live Set. A .als file does not contain your audio: it points at samples by path, and anything outside the Project folder (a Pack, the User Library, a sample on your desktop) goes missing the moment the set opens on another drive or computer. Collect All and Save copies those files into the Project's Samples folder, so the whole Project folder is the backup. Then copy or zip the folder, not the .als.

Back up a Live Set without missing files

A Live Project is a folder. The first time you save a set, Live creates it with the .als inside, an Ableton Project Info folder and, once recorded or collected audio exists, a Samples folder.

1. Open the set and choose File > Collect All and Save.
2. In the dialog, pick which locations to collect from: files elsewhere on your computer, from other Projects, from the User Library and from installed Packs. If the set is leaving your machine, collect everything. Ableton notes you can skip Packs and the User Library when you will never move or uninstall them, but your collaborator does not have your User Library.
3. Copy the whole Project folder to the backup drive or zip it.

Third-party plugins are never collected. Their state is saved inside the set, but the other machine needs the same plugin installed to load it.

Version a Live Set and roll back

Live already keeps versions for you. From the second save on, it writes the previous state of the set into the Project's Backup folder, named with a timestamp in brackets, and keeps the ten most recent per set name. When there are more than ten, the oldest is deleted. Open an older one from the browser or straight from the folder.

Ten saves can be one afternoon. For a version you want to keep (the mix you sent the label, the arrangement before a big edit), use File > Save a Copy with a new name. It writes a separate set and leaves you working on the current one. Different set names also get their own ten backups.

Send a Live Set to a collaborator

Collect All and Save, then send the zipped Project folder. Before you send, freeze or resample any track that uses a plugin the other person does not own, otherwise those tracks open silent. Tell them which Live version you saved with: a set saved in Live 12 does not open in Live 11.

If they only need to listen, send a bounce instead. File > Export Audio/Video renders the arrangement; most feedback does not need the session.

Export stems for mixing or mastering

1. Choose File > Export Audio/Video (Cmd+Shift+R on Mac, Ctrl+Shift+R on Windows).
2. Set Rendered Track to All Individual Tracks to get one file per track, including Group Tracks, Return Tracks and the Main track. Selected Tracks Only renders just the tracks you selected before opening the dialog.
3. Decide on Include Return and Main Effects. Ableton points out this is useful for stems for a live performance or remix. For a mix engineer, leave it off so they get dry stems and add their own space.
4. Export WAV at the set's sample rate, 24-bit or 32-bit float, starting from bar 1 so every stem lines up.

Each file is the post-fader output of its track, so your fader levels and automation are printed into it. Set faders where the mix wants them before you export.

Doing it in Aden

Aden's desktop app reads Live Sets on your disk, which is what makes the steps above harder to forget.

• Your sets, listed. The desktop app finds .als files across your machine (and zips that contain one) and shows them on Home, newest first. A set open in Live right now carries a green dot on macOS, because Live keeps the .als open while you work.
• Sync the Project folder to a track (Max plan). Every save is pushed. A collaborator clicks Pull and gets the latest files; a pull never overwrites their local edits, it saves the incoming file as a versioned copy beside theirs. Every synced file keeps its version history, and each version downloads from the track's Project files page.
• A check before you send. Send as a transfer zips the Project folder into a link that expires in 30 days. When the folder holds little more than the .als, it tells you to run Collect All and Save first.
• Hear the set without Live. On the web, the Project files page reads the set: tempo, key and scale, time signature, tracks, devices, every plugin with its maker and format, every sample path and the arrangement markers. Press play to hear a sketch of the arrangement. Simpler, Sampler and Drum Rack pads play your real samples; third-party instruments get a stand-in sound, and effects and automation are not played.
• Edit and record together. Move or delete clips with everyone who has the page open; Save writes the change into the .als as its next version and keeps every device and plugin setting as it was. Vocal takes recorded in the browser land in an Aden Takes/ folder in the Project, named by the bar to drop them at.
• Feedback on the bounce. Export the mix and the desktop app notices the new file: named after a track you have, it offers it as that track's next version. Send a share link. People comment at a timestamp or on a section of the waveform, and on a link with comments turned on they need no Aden account. Send for review asks them to approve it or request changes, and Compare flips between two mixes at the same playhead. Link the project to that version so you always know which set made which bounce.
• Stems on a version. Upload the stems you exported to the version's Stems tab to line them up and play them together under the mix.
• Aden inside Live. The desktop app installs Aden as a VST3 and Audio Unit plugin on macOS and Windows. Put it on the Main track to see the track's notes, lyrics and session without leaving Live. Audio passes through untouched.

Sources: Ableton Live manual, Managing Files and Sets, Ableton Help, Backup Sets. See also how other DAWs version projects.