September's insider tape was dominated by owners rather than executives. The ten largest open-market transactions of the month were led by holding companies, buyout sponsors, a conglomerate, an investment firm and a corporate partner, with only a handful of individual directors among them. That composition changes how the month should be read: most of the dollar volume reflects portfolio decisions by large holders, and the signal lies in who is adding, who is trimming and on what terms.
Drawing on FMP's Latest Insider Trading API, this article screens every open-market purchase and sale dated in September, aggregates each filer's activity by company, and examines five transactions that stood out for the identity of the filer, the size of the trade relative to the remaining stake, or the corporate context around it.
Key Takeaways
- The month's largest transaction, a sale of close to $1.9 billion in Diamondback Energy stock, came from the family holding company that received shares in the Endeavor merger, and it continues a distribution that began earlier in the year.
- Silver Lake's steady selling of Dell shares through hundreds of small daily trades is a sponsor trimming into strength while keeping a large convertible position, which differs sharply from a full exit.
- Berkshire Hathaway lifted its Lennar stake by roughly a quarter in two weeks, a rare large insider purchase in a homebuilder whose shares have been under pressure.
- Conifer Management's buying in Group 1 Automotive came alongside a new board seat, making it the clearest example in the month of a purchase tied to governance rather than portfolio rebalancing.
Five Ownership Moves Behind September's Biggest Filings
Diamondback Energy, Inc. (FANG)
SGF FANG Holdings, a 10% owner, sold 9,079,675 Diamondback shares at $205.26 on September 16, a transaction worth approximately $1.86 billion and by far the largest open-market disposal of the month. The filer still reported roughly 65 million shares afterwards. SGF FANG Holdings is the vehicle through which the former owners of Endeavor Energy Resources hold the Diamondback stock they received when the two Permian producers combined, and it also sold through an underwritten secondary offering in March.
The repeated sales point to a planned reduction of a concentrated, inherited position rather than a reaction to near-term operating news. For a family holder whose wealth is heavily tied to one stock and one commodity, diversification over time is a logical choice, and Diamondback itself receives no proceeds from these sales. The practical effect is on supply: each tranche moves a large block from a long-term holder into the public float, and the shares have since traded below the September sale price.
The more useful question is how much of the original merger stake remains and at what pace it is being released. FMP's Company Share Float & Liquidity API tracks free float over time, which shows how much tradable supply has been added by each disposal. If the pattern continues, that steady expansion of float is the clearest data point to monitor alongside oil prices and the company's capital return program.
Dell Technologies Inc. (DELL)
Silver Lake's affiliated funds sold Dell Class C shares almost every trading day between September 3 and September 21, with combined proceeds of roughly $820 million across five reporting entities. The trades were small individually, frequently fewer than a thousand shares at a time, but the cumulative total placed Silver Lake second on the month's list. The sales came as Dell's shares traded near record levels, supported by demand for AI servers.
This is not an exit. The filings show the Silver Lake group continues to hold more than 41 million Class B shares, which convert one-for-one into the listed Class C stock, and Silver Lake co-CEO Egon Durban remains on Dell's board. The selling pattern, converting small amounts of Class B into Class C and selling them immediately, looks more like a sponsor gradually realizing gains on a long-held investment than a change in its view of the business. It also limits the market impact that a single large block might cause.
To evaluate the pattern, readers need the full sequence rather than individual filings. FMP's Search Insider Trades by Reporting Name API retrieves every transaction filed by a named holder, which makes it possible to measure Silver Lake's selling pace month by month and compare it with Dell's share price and the remaining Class B balance. A sharp acceleration or a large block sale would mark a departure from the current, measured approach.
Lennar Corporation (LEN)
Berkshire Hathaway bought about 5.1 million Lennar shares between September 17 and September 30 in a series of open-market purchases totaling around $403 million. Its Class A holding rose from roughly 21 million shares to more than 26 million over those two weeks, an increase of close to a quarter, with a smaller addition to its Class B position. It was the largest insider purchase of the month outside Cascade Investment's regular buying in Republic Services.
The timing is the notable feature. Lennar's shares had fallen sharply this year, and the buying began around the company's latest quarterly report, which disappointed on earnings and outlook as heavy sales incentives continued to compress margins. Berkshire has been building the position over several quarters, and this burst of buying adds to that stake rather than starting a new one. A conglomerate with a long investment horizon buying into weakness carries a different message than an executive's personal purchase, but it does indicate a large holder accepting near-term margin pressure in exchange for exposure to housing supply over a longer cycle.
FMP's Filings Extract With Analytics By Holder API shows how Berkshire's quarterly holdings in Lennar and other homebuilders have changed over time, which places this month's Form 4 activity in the context of the broader portfolio. Pairing that with Lennar's gross margin from the Income Statement API would show whether the stake is growing while margins are still declining or as they begin to stabilize.
Group 1 Automotive, Inc. (GPI)
Conifer Management, a 10% owner, bought about 720,000 Group 1 Automotive shares during September across more than a hundred separate transactions, for a total of roughly $187 million. The purchases continued a build-up that took Conifer's stake to close to 10% by mid-August, when it moved from a passive to an active ownership filing and disclosed discussions with the company about board representation.
Those discussions concluded during September, when a Conifer representative was appointed to Group 1's board. That sequence distinguishes this purchase from the others in the screen. Conifer is not a portfolio holder rebalancing or a sponsor monetizing; it is an investor that has gained a voice in governance while continuing to buy. That combination typically signals a long-term commitment and an interest in capital allocation, although Conifer has described itself as a supportive investor rather than one seeking specific changes.
The next filings will show whether buying continues now that board representation is secured. FMP's Company Executives API tracks changes to the board and leadership, which helps connect the governance change to any shifts in strategy, while the Insider Trade Statistics API shows whether other insiders are buying or selling alongside Conifer.
Aurora Innovation, Inc. (AUR)
Uber Technologies sold 29.4 million Aurora shares at about $6.21 on September 15, a transaction worth around $182 million. Uber still reported about 157 million shares afterwards, which represents roughly a tenth of Aurora's outstanding stock, and the sale extends a pattern of reductions over the past year without any purchases.
The context makes Uber's sale different from a financial investor exiting. Uber acquired its Aurora stake when it transferred its own self-driving unit to Aurora in 2020, and the two companies remain commercial partners as Aurora moves its driverless trucking service toward wider deployment. A strategic holder reducing its exposure while keeping a meaningful position and the partnership in place points toward capital management at Uber rather than a break in the relationship. Still, for a pre-profit company whose valuation rests on future deployment, sustained selling by its largest strategic holder adds a steady source of supply.
FMP's Acquisition Ownership API follows changes in beneficial ownership disclosed in Schedules 13D and 13G, which is the most direct way to see if Uber's stake moves below the threshold at which it must keep reporting. That threshold would mark a meaningful change in how visible its future sales are to the market.
Reading Ownership Before Reading Direction
September's largest filings make the case for classifying the filer before interpreting the trade. A family holding company diversifying an inherited stake, a buyout sponsor trimming a successful investment, a conglomerate adding to a homebuilder, an investor joining a board and a corporate partner managing a strategic stake all moved large amounts of stock, but only some of those decisions say anything about each company's near-term prospects. The two purchases carry the clearest information, because neither Berkshire nor Conifer had an obligation or a structural reason to buy.
The sales are more about supply than sentiment. Diamondback, Dell and Aurora are all absorbing stock from large holders whose reasons for selling are structural: diversification, fund lifecycle or a change in strategic priorities. Whether those sales matter for price depends on how much stock remains to be sold, how quickly it is released and whether the market's demand for each name keeps pace.
Testing those questions requires several datasets working together, and the ownership-level coverage available through FMP is what makes that possible. The Insider Trade Statistics API shows whether a single filing sits within a broader pattern of net buying or selling at each company, while the Company Share Float & Liquidity API measures how much tradable supply has been added. For institutional holders like Berkshire, the Filings Extract With Analytics By Holder API places Form 4 activity alongside quarterly 13F positions.
Market data supplies the final check. FMP's Stock Price and Volume Data API shows how each stock traded in the days after a large filing, which helps separate disposals the market absorbed easily from those that weighed on price. Combined with operating data from the Income Statement API, the result is a clearer answer to the question that matters most: who changed their exposure, what limited or motivated the trade, and whether anything in the underlying business changed with it.
Building a Repeatable Insider Research Workflow
Monitoring insider filings manually breaks down quickly once coverage expands, so the first step is to systematize the intake. The workflow starts by pulling recent transactions through the Latest Insider Trading API, which returns a standardized feed of filings — including insider role, transaction type, share count, and execution price — in a format that can be filtered and stored without additional normalization.
If you don't already have one, you'll need to generate your API key before making your first request.
Endpoint:
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https://financialmodelingprep.com/stable/insider-trading/latest?page=0&limit=100 |
Example Response:
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[ { "symbol": "APA", "filingDate": "2025-02-04", "transactionDate": "2025-02-01", "reportingName": "Hoyt Rebecca A", "typeOfOwner": "officer: Sr. VP, Chief Acct Officer", "transactionType": "M-Exempt", "securitiesTransacted": 3450, "price": 0, "securityName": "Common Stock" } ] |
Once those individual transactions are captured, the analysis shifts from event-level review to pattern recognition. This is where the Insider Trade Statistics endpoint becomes useful. By aggregating activity at the ticker level, it surfaces whether insiders are, on balance, increasing or reducing exposure over time rather than reacting to a single filing.
Endpoint:
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https://financialmodelingprep.com/stable/insider-trading/statistics?symbol=AAPL |
In practice, this two-step process — first capturing transaction-level data, then summarizing it into net activity — converts a stream of filings into something analytically usable. It allows you to separate one-off trades from sustained accumulation patterns, which is where insider data starts to carry interpretive weight.
From Individual Signals to Institutional Research
What begins as an individual analyst's workflow often reveals its real value once it's shared. Insider data, when consistently structured and interpreted, tends to surface the same questions across teams: Is this activity isolated or persistent? Is it showing up across related names? How does it align with broader positioning and capital flows? At that point, the challenge is no longer access — it's standardization.
When insider analysis moves beyond a single desktop and into a shared framework, it becomes easier to align interpretation across research, portfolio management, and risk. Centralized datasets allow teams to work from the same signal definitions, apply consistent filters, and review changes over time without rebuilding the logic each cycle. What was once an analyst's custom screen becomes a repeatable input that supports investment discussions across desks.
This is where institutional infrastructure matters. Formalizing insider monitoring through shared pipelines — supported by auditable data sources and common taxonomies — reduces duplication and improves accountability. It also enables downstream integration with portfolio tools, compliance workflows, and internal dashboards, so insights persist beyond the individual who surfaced them. For firms looking to move from ad hoc analysis to a durable research layer, frameworks like the FMP's enterprise plan provide the scaffolding to operationalize that transition without disrupting existing workflows.
The real shift isn't about adding more data; it's about creating continuity. When insider activity is captured, contextualized, and distributed through a common system, it becomes part of the firm's collective intelligence rather than a one-off insight.
Putting September's Filings Into Perspective
The month's biggest numbers came from holders managing large positions, while the clearest signals came from the two that chose to buy. Tracked consistently through FMP's Latest Insider Trading, the distinction between those two kinds of activity becomes easier to see as each new month of filings arrives.
For additional trading ideas backed by data, explore: Signals Desk Weekly Take via FMP API | Five Biggest Stock Movers (Sept 21-25)
Disclosure: Signals Desk content is provided for informational and analytical purposes only and does not constitute investment advice or trade recommendations. The analysis reflects interpretation of market data and publicly disclosed or third-party information, including data accessed via Financial Modeling Prep APIs, at the time of publication. Signals discussed are probabilistic, can be wrong, and may change as market conditions and consensus data evolve. This content should be considered alongside broader research, individual objectives, and risk assessment.
