A GPLv3+ VCV plugin requires its derivative works to also be GPLv3+

GPLv3+ is a copyleft license: any work derived from a GPLv3+ plugin must also be licensed GPLv3+. For VCV Rack this means a developer who copies significant portions of a GPL plugin’s source into their own plugin cannot relicense the result as proprietary — the copyleft prevents turning free code into non-free software without permission. The boundary is what counts as a ‘derived work’: if someone ports the algorithm to a completely different platform (a standalone VST or hardware firmware) so the code is no longer linked to Rack, it is no longer a derived work of Rack, so Rack’s license does not govern that fork.

Examples

Forking a GPL Rack oscillator to add a waveform: the fork must stay GPL. Porting that same algorithm into a standalone VST that does not link Rack: Rack’s GPL does not follow the port.

Assessment

A developer forks a GPLv3+ VCV plugin to fix a bug and redistributes it — must they release source, and why? Then describe a scenario where the Rack GPL would NOT bind the derivative code.