The outcome of a validity challenge at the Patent Trial and Appeal Board (PTAB) frequently depends on a comparison of the challenged claims to asserted prior art. However, as a recent Federal Circuit ruling makes clear, the dividing line between such a comparison and an outright claim construction can be a “fine” one—and this distinction can be critical, because claim constructions receive less deference on appeal. In its precedential Google v. Ecofactor decision, the court held on February 7 that while the PTAB stated that it was not construing a key claim at issue in inter partes reviews (IPRs) filed by Alphabet (Google) and Ecobee, it had in fact done so by effectively limiting the claim’s scope. The Federal Circuit also ruled that this implicit construction had been incorrect as a matter of law, agreeing with the petitioners that the Board had been wrong to reject their invalidity arguments as a result.