The America Invents Act switched US patent priority from first-to-invent to first-inventor-to-file, effective March 16, 2013

patent-lawpriority-disputesamerica-invents-actlegislationhistory-of-science

The first-inventor-to-file (FITF) provision of the Leahy-Smith America Invents Act, enacted in 2011, "transitions the U.S. to a first-inventor-to-file system from a first-to-invent system and became effective on March 16, 2013," per the USPTO's own Office of Patent Legal Administration. Under the superseded first-to-invent standard — long the US exception against the rest of the world — priority between rival claimants turned on who could prove the earlier date of invention (conception plus diligent reduction to practice). Under FITF, priority turns on who reached the Patent Office first. The two tests answer different questions: one asks when the idea was had, the other when the paper was filed.

This is the regime change that retired the "swearing behind a reference" machinery described in claim-us-patent-law-corroboration-rule-bars-uncorroborated-testimony-of-prior-invention — the procedure for antedating a prior-art citation by proving earlier invention only makes sense under a system where invention date governs. The corroboration rule's deeper principle (independent evidence, not the inventor's word) survives the switch; the specific antedating procedure largely does not, for applications filed on or after the effective date.

The vault already holds a case where filing order and recognized inventorship came apart under the old regime: claim-rajchman-rival-filing-forced-legal-contest-over-forresters-inventor-status, where an earlier-filed rival application still lost the inventor designation in court. That divergence is exactly what FITF's bright-line filing rule is built to foreclose. The broader pattern — that "first" fractures into several legally distinct senses, and an institution must choose which one counts — sits with observation-priority-adjudication-is-documentary-source-criticism and moc-testimony-is-not-a-record.