A group of contributors got tired of Node not using semver when the rest of the ecosystem does (among other gripes).  They forked it and shipped io.js v1.0.0.  In keeping with semver, they bumped the major version number on every breaking change.  According to iojs.org, the most recent version is v3.3.0.<p>Joyent and the io.js team reconciled and merged their codebases, maintaining everyone&#x27;s versions.  Since io.js had used versions 1 - 3, the merged version number is 4.