At the moment, the stable release is exclusively for Skylake. The update for older chips remains in beta stage.
Intel has also greatly expanded its document outlining microcode update plans for a wide swath of platforms past. According to this document, Broadwell and Haswell microcode designed to mitigate Spectre remains in beta. Although the company isn't listing every Ivy Bridge product as a candidate for a microcode update yet, it is broadly indicating that firmware for at least some of those CPUs is in pre-beta or beta testing, so it seems likely that most systems with one of those CPUs could eventually get a Spectre-banishing update.Via: The Tech Report