Ableton Live can utilize both VST2 and VST3 formats, with the option to choose which plugin version you load. On Mac, you will also be able to load AU/Component plugins. This is important to note, as each plugin type will have its own default install location.
By default, Ableton Live only has VST2 enabled (on mac it will be VST2 and component) when you first install it. You can enable VST3 by navigating the preferences window and selecting the 'Plug-Ins' tab where you should see the 'Use VST3 Plug-in System Folders'.
Once this option is on you should then have VST3 files enabled.
In terms of install locations, the "System folders" ableton refers to are as follows:
Plugin Type | Mac | Windows |
VST2 | /Library/Audio/Plug-Ins/VST | C:\Program Files\VstPlugins |
VST3 | /Library/Audio/Plug-Ins/VST3 | C:\Program Files\Common Files\VST3 |
AU/Component | /Library/Audio/Plug-Ins/Components | N/A |
These are also the default installation folders that the Spitfire app will use when you first install it. You do also have the option to use custom folders, but this is something we advise against as it is one of the leading causes of install issues within our dedicated plugin libraries.
In the event that you do use a custom plugin folder, you can instruct Ableton to search for that folder by enabling the 'Use VST2 Plugin Custom Folder' or 'Use VST3 Plugin Custom Folder' options, as you will then be prompted to navigate to your custom plugin folders.
More general information on library installation can be found in this article: Where is my library?