Can I work on patent-infringing software in private, then release it when said patent expires?
<p>This is not a scenario I'm actually going through; this is just a thought I had.  <em>The situation proposed in this question is entirely hypothetical.</em></p>

<p>Suppose some algorithm -- for this post, let's say something compression-related -- is patented in the United States.  But the patent is going to 
expire within a year.  I want to add this algorithm to an established project of mine, which is open source and sees both personal and commercial usage.  <strong>Is it legal to privately develop a feature for this project that infringes upon this patent, but withhold releasing it until the day after the patent expires?</strong></p>

<p>For the sake of this post, assume the following:</p>

<ul>
<li>All Git commit history is available and commits are signed; once the patch is released it will be known that I (and possibly others) have worked on this infringing feature while its patent was still active.</li>
<li>I might or might not have announced my development of this patch; I didn't exactly go on a big media blitz about it, but I could have dropped a vague hint (or even an explicit confirm) via Twitter or similar.  I never outright lie about it, though.</li>
<li>The infringing patch is not publicly accessible until the day after the patent expires, but it (or some parts of it) might still have been transmitted to other parties, either for collaboration purposes (e.g. with a friend, storing the patch on his personal server) or when seeking help on support communities like IRC, mailing lists...or StackExchange.</li>
<li>The patch is tested and feature-complete upon release.</li>
</ul>

<p>The whole purpose of a patent is that the contents of the patent becomes public knowledge, in exchange for a time limited monopoly. </p>

<p>Therefore you are allowed to do anything, since you are not just allowed but expected to examine the patent in order to improve on it, except that you need a license to sell or give away products implementing the patent as long as it is valid. </p>

<p>The only thing to be careful about is that by publishing source code, you might be enticing others to infringe on the patent, so I'd recommend not to do that without advice of a lawyer. </p>

<p>PS. With software, the interpretation of "making" software in patent law may be a bit surprising. There was a major case between Microsoft and AT&amp;T about that. The software developer isn't "making" the software. The build engineer putting everything together isn't "making" the software. The CD manufacturer making a million copies isn't "making" the software. The person installing it on their computer is the one who <em>makes</em> it. </p>

<p>I mildly disagree with the claim that "you can do anything", and that the act would be lawful. The law pertaining to patent infringement, <a href="https://www.law.cornell.edu/uscode/text/35/271" rel="nofollow noreferrer">35 USC 271(a)</a>, says</p>

<blockquote>
  <p>Except as otherwise provided in this title, whoever without authority
  makes, uses, offers to sell, or sells any patented invention, within
  the United States or imports into the United States any patented
  invention during the term of the patent therefor, infringes the
  patent.</p>
</blockquote>

<p>Let's apply this to a patented mousetrap. The design specifications for the trap are published, so that a tinkerer can know exactly what object he is prohibited from making. The law does not just limit the sale or offer of sale, it also restricts making and using. If you buy one of those traps at the store, you can assume that you have permission to use the trap: but permission to use does not entail permission to make, and thus buying one trap so that you can better build other copies is also not legal. Such infringement for the purpose of selling knock-offs of the trap adds two things: it adds selling (also forbidden), plus gets into stronger claims for damages. Patent law does not have a "fair use" exception.</p>

<p>It would (probably) be legal to scrutinize the trap and think through how to improve it e.g. by adding a USB port, and you could probably add that feature to a trap that you legally acquired. Once I actually make one of these traps nicluding the protected component, I infringe the patent. Software, however, is existentially different from other stuffs, so it is not clear what counts as "making" or "using" without permission. Corel claims to have patented a software feature "RealTime Preview" for WordPerfect which is <a href="https://search.rpxcorp.com/litigation_documents/11449323" rel="nofollow noreferrer">alleged to have been infringed</a> by Microsoft; their complaint is not based solely on sales, it is also based on making.</p>

<p>This is not to say that you couldn't probably get away with it, but from a legal POV it's not clear how you would do what you describe without unauthorizedly "making" the patented item.</p>

united-states software patents open-source-software