Pedalboard is a wrapper around the JUCE framework (https://juce.com), which is dual-licensed under the GPLv3 or a custom paid commercial license. We chose to license it with the GPLv3 rather than coming up with a dual-license solution ourselves, given that this is an audio processing tool in Python and will usually be used in scripts, backends, and other scenarios where users of Pedalboard are not likely to distribute their code in the first place.

I'm sure they'd love to sell you access under a different license!