Reasonably Continuous Diligence – Not Continuously Reasonable Diligence – Is Required for Reduction to Practice

In inter partes reviews (IPRs) of three related patents, the Patent Trial and Appeal Board (PTAB) invalidated all but one of the challenged claims as anticipated or obvious over various references. The patent owner attempted to “swear behind” these references by offering evidence of prior conception and diligence up to reduction to practice, such as inventor testimony and 1,300 pages of corroborative documents that showed relevant activity on “every business day.” The PTAB agreed that prior conception was established, but held that diligence was not. Specifically, the PTAB found it dispositive that the evidence failed to show “continuous reasonable diligence” as to the claimed features of the invention, because the inventor had also been working on alternative, unclaimed features during portions of the critical period.

The Federal Circuit reversed on appeal, finding the PTAB erred in its application of the law of diligence. The Federal Circuit noted that a patent owner need not prove that the inventor continuously exercised reasonable diligence (as the PTAB required), but rather must show there was reasonably continuous diligence. The Federal Circuit also rejected the PTAB’s position that developing and testing of alternative, unclaimed features during the critical period served to negate diligence, stating that “[d]iligence is not negated if the inventor works on improvements and evaluates alternatives while developing an invention.” Under the correct law, the Federal Circuit held that diligence was shown, and reversed the PTAB’s decisions.