"Immutable.js is still used heavily both within Facebook and in the broader dev community." That does not mean it is alive. It certainly looks like it is dead

"Immutable.js is still used heavily both within Facebook and in the broader dev community." That does not mean it is alive. It certainly looks like it is dead (dead as in it is commonly used when referring to a project that was abandoned), specially since it is backed by Facebook and the last commit was a change on the readme file done in Sep 19, 2016 :/