alt Hacker NewsThe operating system (Sailfish OS) is a mix of components, some open and some closed. Search for "open source" on https://en.wikipedia.org/wiki/Sailfish_OS . They have said years ago that it would be open sourced, but as far as I know the Silica UI is still proprietary.
It was mainly the investors that didn't want to move. Many things were stagnant that needed moving. Now that the investors are gone there is a chance to move things, and slowly things are moving into open sourcing their software.