RESEARCH — THE FILING TAPE #29

One of 83: The Superinvestors' T-Mobile Register Shrank to a Single Holder. Short Interest Is Up 44.3% in a Year.

October 9, 2026

GetCoattail Research — T-Mobile is the market's argument about whether America's fastest-growing carrier still deserves a growth multiple: an earnings beat, raised cash-flow guidance, a 15% dividend increase — and a stock that fell 20.1% in the second quarter and sits 1.2% above its 252-session closing low. We ran it through every filing lens we maintain. One of our 83 superinvestors holds it long — 6,335,783 shares — the tracked cohort's register shrank from four filers to one in Q2, insiders have sold $1,764,668,830.16 of stock in the parsed record against $3,875,379.61 of purchases, and short interest rose 44.3% in a year.

Start with the narrative: the operations delivered; the price did not follow. T-Mobile reported second-quarter 2026 total revenue of $22.79 billion, up 7.9% year over year, with diluted earnings per share of $2.99 against a $2.59 consensus estimate — a $0.40 beat — though revenue came in $0.16 billion below the $22.95 billion expectation. Net income was $3.24 billion. The company added 277,000 postpaid accounts, postpaid service revenue rose 13%, total service revenue rose 9%, core adjusted EBITDA rose 12%, and management lifted full-year adjusted free cash flow guidance to $18.4 billion to $18.8 billion. On September 24 the board raised the quarterly dividend 15%, from $1.02 to $1.17 per share, payable December 10. Targets sit far above the price: MarketBeat's consensus average was $247.84 across 28 analysts on October 3, JPMorgan trimmed its target from $275 to $260 on September 21 while keeping an overweight rating, Scotiabank trimmed $232 to $217 on October 2, and StoneX reiterated a $280 target in coverage on October 5. The stock closed at $163.64 on October 2 in our price file — 1.2% above the 252-session closing low of $161.73 set the day before — and the next report is scheduled for October 28. AltIndex's 24-hour Reddit ranking places T-Mobile fifth, at 75 mentions, up 134.4% — the highest-ranked stock we had not yet audited.

Now the filings. GetCoattail tracks the investors best placed to know any company: superinvestors, institutions, insiders, Congress, and 5% holders. For T-Mobile — the twenty-ninth Filing Tape audit — the story is absence and control: a superinvestor register with a single name on it, a congressional record that is entirely blank, insider selling measured in billions against purchases measured in millions, a borrow that grew over the year — and, above all of it, a controlling holder whose 13D register has stepped down from 59.0% to 53.7%.

Lens 1: the superinvestors — one holder left, and it raised its stake

We track 83 large, mostly long-only managers whose 13F portfolios we collect directly from SEC EDGAR. As of June 30, 2026, 1 held T-Mobile long — a long row, no option rows — totalling 6,335,783 shares worth $1,062,700,883. The direction count is a single word: one increased.

The one holder is Dodge & Cox Funds, with 6,335,783 shares worth $1,062,700,883, a 0.56% portfolio weight, increased 2.9% from 6,157,799 shares at March 31. A quarter earlier, the tracked register had four filing rows totalling 9,128,300 shares: Dodge & Cox's 6,157,799, Viking Global Investors' 2,967,374 shares, Maverick Capital's 2,152 shares and Pzena Investment Management's 975 shares. In the second quarter only the Dodge & Cox row remains, so the cohort total fell 30.59%, from 9,128,300 shares to 6,335,783. Our EDGAR collection's exit lists record Maverick and Pzena as exited; the Viking row has no second-quarter counterpart in either collection, and we state it no more strongly than that. In a quarter when the price fell 20.1%, from $210.03 to $167.73, the register's shape changed more than its survivor's position did: the holder that stayed added 2.9%. The cohort's reported value implies $167.73 per share, matching the June 30 close exactly, and the EDGAR collection and the pipeline's CUSIP file agree on the second-quarter total to the share and to the dollar.

T-Mobile through six filing lenses
Chart 1: Signal presence by cohort. Superinvestors: 83 managers, 2026Q2 13F (as of Jun 30, 2026). Institutions: full-market 13F aggregation, same date. Insiders: Form 4 record through Oct 2, 2026. Congress: Senate and House PTR records through Oct 3, 2026 (no T-Mobile record in either). 13D/G: filings through Mar 23, 2026. Short interest: FINRA biweekly settlement data through Sep 15, 2026. Source: SEC EDGAR; FINRA; GetCoattail collections.

Lens 2: institutions — fewer filers, 15.21% more shares

Zoom out to the whole 13F market and the register is broad. At June 30, 2026, 1,661 institutions reported positions, down from 1,706 at March 31 (−2.64%), and 1,655 reported long positions. Reported shares rose 15.21%, from 399,805,217 to 460,613,214 shares, with 1,330 filers entering and 1,375 exiting. Reported aggregate value fell 3.92% to $75,675,850,124; the aggregate includes option rows, so we headline filer and share counts and label dollars "reported" (see methodology). The implied value per share, $164.29, sits 2.1% below the June 30 close of $167.73. The full market consolidated — fewer filers holding more shares — in the same quarter the tracked cohort's register shrank to a single name and its share count fell 30.59%.

Lens 3: the 5% register — a controlling holder stepping down, in amendments

Eight SC 13D/G filings cover T-Mobile in our full parse — all eight are SC 13D/A amendments, with nine reporting persons across them and the most recent filed March 23, 2026. This register is dominated by the controlling holder. The Deutsche Telekom group — Deutsche Telekom AG and its holding subsidiaries, reporting the same stake jointly, so the rows are never summed — reported 670,278,284 shares (59.0%) as of June 12, 2025, then 648,359,244 shares (57.1%) as of June 17, 2025, 636,411,404 shares (56.5%) as of August 8, 2025, 628,168,603 shares (55.8%) as of October 2, 2025, and 592,065,875 shares (53.7%) as of March 19, 2026 — down 11.7% in shares from the June 2025 row, in five steps, each printed in an amendment. The register's second group moved the same way faster: SoftBank Group Corp. reported 63,861,065 shares (5.62%) as of June 17, 2025, and 50,861,065 shares (4.52%) as of August 6, 2025 — down 20.4%, and below the 5% reporting line. We report the rows as filed and do not sum them: the aggregate's combined field adds group members and different dates together, which would multiply-count the same stakes (see methodology). Nothing in this register is newer than March 23, 2026.

Lens 4: insiders — $1.76 billion of sales against $3.88 million of purchases

The parsed Form 4 record holds 140 filings through October 2, 2026. Across it, open-market purchases total 3 transactions, 18,705.09 shares and $3,875,379.61, by two buyers. Against that stand 457 sales totalling 7,467,696.13 shares and $1,764,668,830.16, by fifteen sellers, 31 of the 457 recorded as officer sales. The last year holds both purchase transactions that carry size — 2 transactions, 14,897.44 shares, $2,977,851.78, both recorded as officer purchases — against 101 sales totalling $417,921,147.86 by ten sellers. The last 90 days are nearly empty: zero purchases and one sale — 772 shares, $137,670.76, by one seller, recorded as an officer sale. Our site's insider aggregate (October 10, 2026) matches the full-parse 90-day figures exactly — one sale, one seller, $137,670.76 — so for this name the two collections agree. Some selling is mechanical — vesting, tax withholding and pre-arranged plans — and we assign no motives to any of it; the record's shape is what it is: billions out, millions in, and a quiet last 90 days.

Lens 5: Congress — no record in either chamber

Across the congressional record we maintain (combined record as of October 3, 2026), T-Mobile has no record at all — no purchase transactions, no sale transactions, no member rows. The House aggregate (as of October 3, 2026) carries no T-Mobile record, and neither does the Senate aggregate (as of October 1, 2026). We report the absence rather than omitting the lens: in a series where most large caps print at least a handful of congressional trades, this register is blank in both chambers.

Lens 6: short interest — up 44.3% in a year, at 1.68% of the share count

As of September 15, 2026 — the most recent FINRA settlement date — 18,071,400 T-Mobile shares were sold short, with days-to-cover of 4.57, up 5.72% from the prior settlement. Year over year the borrow is up 44.3%, from 12,525,411 shares on September 15, 2025. The series peak stands at 32,187,667 shares on March 31, 2023, so the latest reading is 43.9% below the peak; the June 30, 2026 settlement recorded 20,010,780 shares, so the borrow has eased 9.7% since quarter-end even as it rebuilt over the year. Against the 1,072,671,613 shares in our fundamentals file (as of July 17, 2026), the borrow is 1.68% of the reported share count.

Short interest in T-Mobile
Chart 2: Shares sold short in T-Mobile at each FINRA biweekly settlement, Jan 2024 – Sep 15, 2026 (n = 65 settlements in the chart window; the full collected series runs 137 settlements from Jan 15, 2021). The window high is 27,805,490 shares on Jan 31, 2024; the maximum of the full collected series is 32,187,667 shares on Mar 31, 2023, before the chart window. The latest reading, 18,071,400 shares on Sep 15, 2026, is 43.9% below that peak and 44.3% above the 12,525,411 shares recorded on Sep 15, 2025. Source: FINRA Equity Short Interest files; GetCoattail collection (tmus_short_interest_series.csv).

The recent settlements run 22,533,542 on July 15, then 18,076,785, 16,943,967, 17,093,779 and 18,071,400 — a July spike that unwound, then two settlements of rebuilding. The series began at 11,965,094 shares on January 15, 2021; its lowest reading is 9,709,194 on August 31, 2021. At 1.68% of the share count the borrow is not large; its direction over the year — up 44.3% while the price fell — is the fact in this lens.

The gap, stated plainly

The registers describe a stock whose operating story is growth while its filing record is thinning and controlled. One of 83 tracked superinvestors holds T-Mobile, up 2.9% as a holder; the cohort around it went from four filers and 9,128,300 shares to one filer and 6,335,783 shares in a single quarter, a fall of 30.59% in a quarter when the price fell 20.1%. The full market moved the other way on shares — filers down 2.64% to 1,661, reported shares up 15.21% to 460,613,214. Above both registers, the 13D file describes the real structure: Deutsche Telekom at 592,065,875 shares (53.7%), down from 59.0% in five amendment steps, and SoftBank below the 5% line at 4.52% after a 20.4% cut. Insiders have sold 457 transactions totalling $1,764,668,830.16 in the parsed record against 3 purchases totalling $3,875,379.61, with one sale in the last 90 days. Congress registers nothing in either chamber. And the borrow, at 18,071,400 shares and 1.68% of the share count, is up 44.3% in a year. One plausible reading is that the free-float registers are being reshaped from above: a controller trimming in steps, a second anchor holder below the reporting line, tracked conviction narrowed to a single name — while the operating numbers that drive the narrative print after these registers, not before them. The record supports each clause separately; it does not say which register is right.

What would change the picture

Nothing above is a recommendation. It is a record. These are the filings that would change the description:

Until one of those prints, the record describes a stock held by one of our 83 tracked superinvestors — 6,335,783 shares, the register down from four filers and 30.59% fewer shares in one quarter — whose controlling holder has amended its stake down from 59.0% to 53.7% in five steps, whose second anchor holder sits below the 5% line, whose insiders sold $1,764,668,830.16 in the parsed record against $3,875,379.61 of purchases, whose congressional register is blank in both chambers, and whose borrow, at 18,071,400 shares, rose 44.3% in a year to 1.68% of the share count.

Related reading: Seven of 83: One Holder Is 62.8% of the Superinvestors' Spotify Stake. Its Insiders Have Never Bought a Share. — Filing Tape #28; Twenty of 83: The Superinvestors Cut Disney Shares 20.0% While the Full Market Added 16.2%. — Filing Tape #27; Zero of 83: The Superinvestors Aren't in IREN — Filing Tape #1. T-Mobile's own page: T-Mobile US, Inc. (TMUS) on GetCoattail.

Methodology and data notes

This article describes public filings as of the dates stated. It is not investment advice and makes no recommendation. Filings lag reality: 13F positions are as of June 30, 2026, and later trading is not yet public.

Revision history

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