Not certainly, but you can check for it, via phone update, check without being singed to a any Insider unless it is Insider Production program, or with WDRT, after phone is running W10M, when W10M officially will be released for 8.1 or older phones, there definitely will be a firmware for a devices to optimize them for W10M OS, and recently some said, that W10M is being push slowly to older phones, some said that 535 and some 640 users got an official update to upgrade to a W10M from 8.1. that means there will be firmware too.