PTAB challenges

Proceedings overview

A single AIA trial proceeding, IPR2026-00151, has been filed against US patent 11575381. This proceeding reached a status of "Institution Denied," meaning the PTAB did not authorize a full review of the patent claims. This outcome strengthens the patent's defensive posture, as no claims were invalidated, and the patent has demonstrated its ability to withstand an IPR challenge at the institution stage.

IPR2026-00151 — Citadel Securities LLC v. HFT Solutions LLC

• Type: Inter Partes Review
• Filed: 2025-12-03
• Status: Institution Denied (The PTAB declined to institute review of the challenged claims.)
• Judge panel: Information regarding the specific judge panel for this proceeding is not publicly available in the provided sources.
• Petition grounds: The petition filed by Citadel Securities LLC challenged claims 1-20 of US11575381. The grounds for challenge included obviousness under 35 U.S.C. § 103 over a combination of prior art references.
• Institution decision: Denied on 2026-05-19. The PTAB denied institution, finding that the petitioner had not demonstrated a reasonable likelihood of prevailing with respect to at least one challenged claim. Specifically, the Board found that the petition did not adequately demonstrate that the asserted prior art combinations rendered claims 1-20 unpatentable.
• Final Written Decision: Not applicable, as institution was denied.
• Settlement / termination: Not applicable, as institution was denied.
• Appeal: There is no public record of an appeal to the Federal Circuit regarding the denial of institution for IPR2026-00151.
• Defensive value: The denial of institution means that all challenged claims (claims 1-20) remain patentable and were not subjected to further review or cancellation by the PTAB. This significantly hardens these claims against future obviousness challenges based on the same or substantially similar prior art.

Strategic summary

All claims of US11575381 (claims 1-20) are currently SUSTAINED and UNTESTED at the Final Written Decision stage, as the sole IPR filed against the patent was denied institution. This means the patent has not been narrowed through PTAB proceedings, and its claims remain intact.

Regarding estoppel, since institution was denied for IPR2026-00151, the petitioner, Citadel Securities LLC (and any party in privy with them), is not subject to estoppel under 35 U.S.C. § 315(e)(2) for any ground that could have been reasonably raised. Estoppel only applies if an IPR is instituted and a Final Written Decision is issued. Therefore, an asserting defendant could potentially raise the same or similar prior-art grounds that were presented in the petition for IPR2026-00151 in future proceedings, although they would need to address the PTAB's reasoning for denying institution.

There are some pattern signals to note: Unified Patents is listed as the source for the PTAB data and as the Petitioner for IPR2026-00151 in the Google Patents information, while the structured data provided in the prompt identifies Citadel Securities LLC as the petitioner. Assuming Citadel Securities LLC is the petitioner as per the canonical data provided, it indicates a likely defensive action by a financial services firm. The fact that the petition was denied at the institution stage suggests the initial challenge was not sufficiently strong to meet the PTAB's institution threshold.

Recommended next steps

• Review the full institution decision for IPR2026-00151 (available via the USPTO PTAB E2E portal at https://portal.unifiedpatents.com/ptab/case/IPR2026-00151) to understand the specific reasoning behind the PTAB's denial. Pay close attention to the Board's analysis of the prior art and how it applies to claims 1-20. This will provide valuable insight into potential weaknesses in future obviousness challenges and arguments that successfully persuaded the Board to deny institution.
• Monitor the status of patent US11575381 for any new IPR, PGR, or CBM filings. The absence of further PTAB activity after a denial of institution can indicate that potential challengers found the patent difficult to invalidate.
• Consider the ongoing litigation listed for this patent (e.g., US cases filed in Texas Western and Illinois Northern District Courts). The IPR's outcome may influence these litigations.