US 9886421

I'll start by checking authoritative sources for this exact patent, plus any 2026 CAFC activity.

Good — I have partial claim text. Now let me pin down the full independent claim set and check for any 2026 appellate activity.

Let me confirm the 2026 appellate posture and the IPR outcome, plus the full independent claim set.

US 9,886,421 — Summary

Caveat up front: I could not query USPTO Patent Center or the CAFC docket system directly. What follows is assembled from Google Patents (the authoritative full text you supplied), FreePatentsOnline, Patexia, Justia, the CAFC's own opinions page, and PTAB/IPR filings surfaced via search. Items I could not verify independently are flagged.

Bibliographic data

Continuation chain: 09/906,444 (7/16/2001, abandoned) → 11/443,664 (5/30/2006) → US 8,522,127 → 13/956,265 (7/31/2013, abandoned) → 14/793,643 (7/7/2015) → US 9,405,735 → 15/197,389 (6/29/2016) → US 9,892,093 → 15/581,921 → US 9,886,421.

Abstract

When a browsing computer navigates to a network document such as a web page, the server also downloads computer-readable formatting information needed for the browsing computer's operating system to correctly render characters in the document even if the associated fonts did not previously exist on that computer. An exposure module is downloaded too; it permanently installs or temporarily exposes the OS to that font formatting information, so the document displays correctly and consistently regardless of which fonts are installed locally.

Plain-language overview of the independent claims

Claims are 1–17; 1, 6, and 11 are independent (12–17 depend from 11, per PTAB filings). I have verbatim text for claim 1 and near-verbatim text for claims 6 and 11; minor wording drift in 6/11 is possible.

Claim 1 — a non-transitory computer-readable medium (server-side article)
A storage medium usable with a network-connected computer and accessible to a hand-held device running an operating system. It contains three things:

1. an electronic file package with display characters plus code that identifies which characters to display and which external fonts render them;
2. a font package of external font files containing the formatting information the hand-held device needs to render those characters — and it must be separate from the character-identifying code;
3. an exposure module that installs the font files into a temporary fonts directory on the hand-held device.

The font files arrive from the computer in response to a request from the hand-held device; the characters then render via a program module of the operating system (not a plug-in viewer), and installing the font files causes the device's system font table to be updated to reflect their availability.

Claim 6 — a computer-implemented method (client-side)
A hand-held device whose OS recognizes only a standard set of fonts requests a network document from a server. The document includes an application file identifying the display characters and code identifying a font not in the standard set. The device receives a font package separate from the application file and referenced by the document's code; that package's formatting information lets the OS — and other applications controlled by the OS — render the character. On accessing the document, the device installs the formatting information into a temporary fonts directory and updates the system font table. The "other applications" language captures the core inventive point: the font becomes OS-usable for copy/paste/print, not siloed in one viewer.

Claim 11 — a hand-held device (apparatus)
A device with a display, processing unit, and memory storing instructions that cause it to: communicate with the network computer; download an electronic file containing code identifying two or more display characters and the font used to render at least one of them, where that code references a font package with the formatting information necessary for the device's OS to render the character; install an exposure module that automatically installs or exposes the package; cause the exposure module to install at least a portion of the font package to a temporary fonts directory so an OS program module can render the character; and cause the system font table to be updated to reflect the font's availability.

One-line takeaway: all three independents require (a) a font package delivered with/referenced by the network document, (b) an exposure/installation module that puts it into a temporary fonts directory, and (c) a system font table update so the OS itself — and other applications — can render non-standard fonts.

Uncertainty note: I do not have the complete verbatim dependent-claim set (2–5, 7–10, 12–17). PTAB petition excerpts reference additional limitations (e.g., "saving font rendering information… to an internal memory of the hand-held device"), so the exact wording of some claims should be confirmed against the printed patent.

Litigation and validity posture (including 2026 CAFC activity)

This patent has been heavily litigated and is now adjudicated invalid:

• District court campaigns by Modern Font Applications LLC against app developers/users — D. Utah (2:18-cv-00649, -00658; 2:19-cv-00211, -00213, -00214, -00221, -00561, -00613, -00614), C.D. Cal. (8:19-cv-01660, -01699), E.D. Tex. (4:18-cv-00618; 6:18-cv-00444, -00446; 6:19-cv-00233, -00234, -00235), W.D. Tex. (6:21-cv-00470, asserted against Red Lobster), N.D. Cal. (3:21-cv-05305, -06132, -07521).
• IPRs: IPR2022-00799 (CoStar Realty Information + Duolingo; challenged claims 1–17; Final Written Decision) and IPR2022-00435 (Coinbase; settled). The '421 claims were held unpatentable as obvious over Collins, Gautier, Schaefer (Ground 1) and further in view of Parthasarathy (Ground 2).
• 2026 CAFC docket — the item you asked about: Clantech, Inc. & Modern Font Applications LLC v. CoStar Realty Information, Inc. & Duolingo, Inc., Nos. 2024-1360, 2024-1361 (appeals from IPR2022-00799 and IPR2022-00800). The panel (Lourie, Reyna, Cunningham) issued a Rule 36 affirmance on December 11, 2025 (nonprecedential, no opinion). Appellants filed a combined petition for panel rehearing and rehearing en banc on January 12, 2026, raising three questions: claim-term consistency within a claim, APA/institution-grounds switching (EmeraChem, SAS, etc.), and inventor-corroboration standards. That petition was denied on February 13, 2026 (per curiam; the '421 patent's own text is Appendix pages 120–138 of the joint appendix).

Earlier family appeals on the CAFC docket (20-2278, 21-1543, 21-1838, 22-1215) appear related to sibling patents/appeals rather than this specific IPR; I did not verify each one, so treat that mapping as tentative.

Practical bottom line: as of today (April 26, 2026), the '421 patent is expired and its claims stand cancelled/held unpatentable, with the Federal Circuit's affirmance now final after the February 13, 2026 denial of rehearing.

Minor identifier artifact (not corrected, per your instruction): one IPR2022-00435 exhibit header reads "U.S. Patent No. 9,866,421" while that same document's body and index repeatedly reference "9,886,421." I am reporting the discrepancy rather than silently harmonizing it; the balance of the record indicates a typographical error in that filing's header.

Where I have low confidence: exact claim text of dependent claims; the precise expiration date (2021-07-16 vs. 2022-02-06); and whether current record ownership rests with Clantech or Modern Font Applications (the March 2024 record is a license, while pleadings and IPR papers sometimes describe MFA as owner/patent owner).