Given that the API is to be released under GPL. Does this mean that all plugins for it must also be open sourced? Most plugin authors include their source in the .jar file, but not all. In many cases, that is probably that they didn't bother. However,that is not likely to be the case for all. What counts as a derivative work is still reasonably grey for GPL with regards to plugins. Some say that plugins are completely separate programs and some say that are effectively a combined work. OTOH, the actually linking is being handled by the end user. Ofc, you guys seem to be planning to have a central location for plugins, so that brings it back to being distributed from one source.