Inter partes review (IPR) proceedings before the Patent Trial and Appeal Board (PTAB) are widely regarded as challenger-friendly, in significant part because of the burden of proof applied to patent validity. 

Unlike district court litigation, where an issued patent enjoys a statutory presumption of validity and may be invalidated only by clear and convincing evidence, an IPR petitioner need only establish unpatentability by a preponderance of the evidence. This lower evidentiary threshold substantially reshapes the strategic landscape for patent challenges.

The IPR preponderance standard rationale rests on the institutional competence of the PTAB: technically trained administrative judges, constrained claim construction, and a focused, printed publication prior-art record. Within this framework, the heightened deference traditionally afforded to issued patents in court is viewed as less necessary.

The practical impact has been pronounced. A petitioner need only show that it is more likely than not that a claim is anticipated or obvious, rather than proving invalidity to a high degree of certainty. There is no jury that might not understand the technology or make decisions contrary to the evidence. This difference is often outcome-determinative, particularly in close cases involving nuanced teachings in prior art references or marginal distinctions in claim scope. Empirical studies consistently show higher invalidation rates in IPR compared to district court proceedings, reinforcing perceptions of a petitioner-friendly forum. While patentees retain procedural protections, the preponderance standard remains a central reason why IPRs have been a powerful and frequently used tool for patent challengers.

However, the recent trend emerging from the USPTO has changed the balance, particularly for older patents. “The USPTO has made clear that it prefers challenges of patents early in their lifespan, promoting PGRs with their nine-month deadline over open-ended IPRs — although the agency still has a high standard for PGRs,” according to a Law360 analysis of patent litigation trends to watch in 2026. Read more here. 

Patentees should and will consider asserting their older patents in their portfolio before the USPTO has a change of heart or change of administration. Potential defendants should prepare accordingly.