PTAB challenges

Proceedings overview

Currently, one AIA trial proceeding is on file for US patent 8478903, which is in active trial. The current defensive posture for a defendant is that one IPR is pending institution and no claims have been invalidated or sustained by the PTAB yet.

IPR2026-00095 — Microsoft Corporation v. Mount Shasta Acquisition LLC

• Type: Inter Partes Review
• Filed: 2025-11-03
• Status: Trial Instituted (The PTAB has decided to initiate a trial on the merits of the petition).
• Judge panel: APJ Young (Acting Lead Judge), APJ Paul (Administrative Patent Judge), and APJ Boni.
• Petition grounds: Microsoft Corporation petitioned against claims 1-20 of U.S. Patent No. 8,478,903. The petition asserts grounds of unpatentability under 35 U.S.C. § 103 as obvious over various combinations of prior art, including references such as US 6,178,449 B1 (Freedman), US 6,108,703 A (Leong et al.), US 5,850,523 A (Hirata et al.), US 6,434,622 B1 (Armijo et al.), and US 6,161,130 A (Chester et al.).
• Institution decision: Instituted on 2026-05-01. The panel found that the Petitioner, Microsoft Corporation, demonstrated a reasonable likelihood of prevailing with respect to at least one challenged claim, allowing the trial to proceed.
• Final Written Decision (if issued): Not yet issued. The trial was instituted on 2026-05-01, and a Final Written Decision is typically due within one year of institution.
• Settlement / termination: Not applicable; the proceeding is active.
• Appeal: Not applicable; no Final Written Decision has been issued.
• Defensive value: This proceeding indicates that all claims (1-20) of US8478903 are currently under review for obviousness at the PTAB. While no claims have been canceled yet, the institution decision suggests that Microsoft has a reasonable likelihood of success on at least some of the challenged claims. A defendant facing assertion of this patent should closely monitor this IPR, as a successful outcome for Microsoft could significantly weaken the patent.

Strategic summary

US patent 8478903 currently has all claims (claims 1-20) under active review in IPR2026-00095. None of the claims have been formally canceled or sustained by the PTAB yet, as the proceeding is still in the trial phase. There are no claims listed as sustained or definitively untested, as Microsoft challenged all claims and the PTAB instituted the trial. The patent owner for this proceeding is Mount Shasta Acquisition LLC.

Regarding the estoppel landscape, if IPR2026-00095 proceeds to a Final Written Decision, Microsoft Corporation and its privies would be estopped under § 315(e)(2) from asserting in future district court or ITC actions any invalidity grounds they raised or reasonably could have raised during this IPR concerning claims 1-20. For other potential defendants, the grounds asserted by Microsoft (various obviousness combinations) would still be available for challenges in new IPR petitions or in district court, assuming those defendants are not in privity with Microsoft. The patent owner, Mount Shasta Acquisition LLC, is actively defending the patent.

Recommended next steps

For a defendant currently being asserted against using US patent 8478903:

• Monitor IPR2026-00095 closely. The proceeding is currently in the trial stage, which means key milestones like expert discovery, oral hearing, and the Final Written Decision are yet to occur. The statutory deadline for the Final Written Decision is typically one year from the institution date (May 1, 2026), so expect a decision around May 1, 2027.
• Review the institution decision for IPR2026-00095 to understand the PTAB's initial reasoning for finding a reasonable likelihood of Microsoft prevailing on claims 1-20. The institution decision is available on the USPTO PTAB E2E system.
• Given that all claims are challenged, a favorable outcome for the petitioner (Microsoft) could significantly diminish the value of the patent. If the asserted claims are among those invalidated, it could provide a strong defense.