See, “First to File” doesn’t require that you build
anything at all, that you have an intention to build
something, or that you’re getting a patent on something
that hasn’t, you know, already been invented by someone
who couldn’t afford the patent.
First to file makes no changes to any of that. It all remains exactly the same as it was under first to invent.All that first to file changes is what happens when two (or more) separate inventors, who meet all of the statutory requirements for patentability (e.g., novelty, utility, non-obviousnous, reduction to practice and enablement), both file for patents.
Under first to invent, you try to figure out when each inventor actually started working on reducing the invention to practice (just having the idea is not enough). You find the earliest time T such that the inventor was working diligently on reduction to practice between T and the time of the patent application. T is that inventors invention date. Lowest date wins.
Under first to file, you look at the date on the application. Lowest date wins.
First to invent is problematic because it comes down to comparing two or more vague dates, and there can be a lot of subjectivity involved, such as deciding whether or not an inventor was working diligently or not toward reduction to practice.