13D and 13G Beneficial Ownership API: Activist and Passive 5% Stakes as Clean JSON

A 13D and 13G beneficial ownership API answers one question fast: who owns more than 5% of a company, and are they passive or activist? The StockFit /api/ownership/beneficial-owners endpoint returns every Schedule 13D and Schedule 13G filer for a ticker as clean JSON, each stake tagged with its filingType, its percent of class, and the SEC accession number it came from. This post is a product walkthrough of that endpoint and its history sibling, with verified live data on a real activist situation.

The thesis is the one StockFit leads with everywhere: the data is parsed straight from SEC EDGAR and every value carries its accession number, so an ownership signal is traceable back to the exact filing instead of arriving as a normalized number with no provenance. For a position that can move a stock on disclosure, that audit trail is the difference between a tradable signal and a rumor.

What Schedule 13D and 13G disclose, and the 5% trigger

Under Sections 13(d) and 13(g) of the Securities Exchange Act, anyone who acquires beneficial ownership of more than 5% of a voting class of a registered equity must disclose it. Which form they file encodes their intent. An investor who means to influence or control the company files a Schedule 13D. A passive holder, an index fund, an ETF sponsor, a qualified institutional investor with no control intent, files a Schedule 13G. The threshold and the intent are the whole story, and they are exactly what the endpoint surfaces.

Match Group (MTCH), the owner of Tinder and Hinge, is a clean live example of both sides at once. Its 5% holder list is dominated by passive index giants filing 13Gs, with one activist filing a 13D: Starboard Value, run by Jeffrey Smith, the investor who has campaigned at Match before. The chart below is built entirely from the verified endpoint response.

Four passive 13G holders (BlackRock, Vanguard, Ameriprise, State Street) and one activist 13D (Starboard). Read off the filingType field and you have the passive-versus-activist split without parsing a single cover page. For the wider map of which SEC forms carry what, see our guide to SEC forms.

Why the raw EDGAR 13D and 13G feed is hard

Pulling this from EDGAR yourself is more work than it looks. Three problems compound.

The filings are CUSIP-keyed and historically unstructured. A 13D or 13G identifies the security by CUSIP on a cover page, not by ticker, so you first have to map CUSIP to issuer. For most of the form's history the cover page was free text and an exhibit, which means scraping percentages, share counts, and reporting-person tables out of prose that every filer formats differently.

Positions arrive as deep amendment chains, not snapshots. Activists do not file once. Starboard's involvement with Match shows up as a long string of Schedule 13D amendments: the StockFit /api/filings feed returns more than 120 13D and 13G filings for MTCH going back to 2017. To know the current stake you have to find the latest amendment per reporting person and ignore the superseded ones, per group, across years.

The format changed in 2023. The SEC's Modernization of Beneficial Ownership Reporting shortened the initial 13D deadline from 10 calendar days to 5 business days, set 13D amendments at 2 business days, and mandated that the schedules be filed in a structured, machine-readable format. You can see the transition in the data: the 2026 Starboard 13D is XBRL-tagged, while the older filings in the same chain are not. A parser has to handle both the new structured cover pages and the legacy free-text ones. The official definitions of who files which live on Investor.gov.

StockFit absorbs all three problems and hands you the resolved current position per holder, with the accession number kept so you can always go back to the source.

The beneficial ownership API, with live JSON

One call returns the current 5% holders for a ticker, latest filing per reporting person:

curl 'https://api.stockfit.io/v1/api/ownership/beneficial-owners?symbol=MTCH' \
  -H 'Authorization: Bearer $STOCKFIT_API_KEY'

Two rows from the live response, the activist and the largest passive holder, trimmed to the fields that matter. Key off filingType for the 13D-versus-13G distinction:

[
  {
    "reportingPersonName": "Starboard Value LP",
    "filingType": "13D",
    "percentOfClass": 4.6,
    "aggregateAmountOwned": 10833200,
    "typeOfReportingPerson": "PN",
    "securityClassTitle": "Common Stock, $0.001 par value",
    "reportDate": "2026-05-06",
    "accessionNumber": "0000902664-26-002298",
    "filingUrl": "https://www.sec.gov/Archives/edgar/data/891103/000090266426002298/primary_doc.xml"
  },
  {
    "reportingPersonName": "BlackRock, Inc.",
    "filingType": "13G",
    "percentOfClass": 11.9,
    "aggregateAmountOwned": 27660359,
    "typeOfReportingPerson": "HC",
    "securityClassTitle": "Common Stock",
    "reportDate": "2026-04-08",
    "accessionNumber": "0002012383-26-001051",
    "filingUrl": "https://www.sec.gov/Archives/edgar/data/891103/000210011926001051/primary_doc.xml"
  }
]

The accessionNumber and filingUrl are the audit trail. Paste the accession into /api/filings/search-by-accession-number or open the filing URL and you land on the exact SEC document the number came from. This is the structural difference from a normalized ownership table: a vendor that returns "Starboard owns 4.6%" with no provenance cannot show you which filing that is, or let you verify it. The typeOfReportingPerson codes are the SEC reporting-person categories (PN for partnership, HC for parent holding company, IA for investment adviser, IN for individual), so a filing group like Starboard's many partnership entities is legible rather than a wall of near-duplicate names.

Detecting the 13G-to-13D activist switch

The highest-value event in this dataset is a holder switching from a passive 13G to an active 13D on the same stock. That flip means a previously passive investor now intends to influence the company, and it routinely moves the price on the day it files. A snapshot endpoint that only shows the latest filing per owner cannot reconstruct it, because the prior 13G has been superseded.

That is what the history endpoint is for. /api/ownership/beneficial-owners/history returns every filing per reporting person over time, each tagged with its filingType and reportDate, rather than collapsing to the latest. The switch is then a simple scan: for a given reporting person, a 13G followed later by a 13D is the passive-to-activist flip.

curl 'https://api.stockfit.io/v1/api/ownership/beneficial-owners/history?symbol=MTCH' \
  -H 'Authorization: Bearer $STOCKFIT_API_KEY'

Each row carries the filing type and the date it was reported, so the full passive-or-active timeline per holder is reconstructable:

[
  {
    "reportingPersonName": "Starboard Value LP",
    "filingType": "13D",
    "percentOfClass": 4.6,
    "aggregateAmountOwned": 10833200,
    "reportDate": "2026-05-06 00:00:00",
    "accessionNumber": "0000902664-26-002298"
  },
  {
    "reportingPersonName": "BlackRock, Inc.",
    "filingType": "13G",
    "percentOfClass": 11.9,
    "aggregateAmountOwned": 27660359,
    "reportDate": "2026-04-08 02:53:47.485",
    "accessionNumber": "0002012383-26-001051"
  }
]

Because each row keeps its own filing date, the switch detection is honest: you see the 13G when it was the truth and the 13D when it became the truth, with no overwrite. The same history powers a stake-building view (watch an activist's percent of class climb across amendments) and a de-escalation view (an activist dropping below 5% and going quiet). For turning an ownership signal into a backtest, our insider cluster-buy study shows the event-study mechanics on a sibling SEC dataset.

Beneficial vs institutional vs insider ownership: which to use

SEC ownership data comes in three families that answer different questions. Picking the wrong one is the most common mistake here.

Beneficial ownership (Schedule 13D and 13G)

Large concentrated stakes above 5%, with the passive-or-activist intent attached. Use it to answer "who are the big strategic holders, and is anyone trying to influence this company?" This is the /api/ownership/beneficial-owners family. The /api/ownership/summary endpoint rolls beneficial owners, institutional concentration, and insider count into one snapshot.

Institutional ownership (Form 13F-HR)

Every position above the reporting threshold held by institutional managers with over $100M under management, filed quarterly. Use it to answer "which funds hold this, and how did positions change last quarter?" It is broader and lower per-line than 13D/13G, and it lags up to 45 days after quarter end. A dedicated 13F walkthrough is coming to this blog; for now the difference is the point: 13F is the wide institutional book, 13D/13G is the concentrated 5% strategic stake.

Insider ownership (Forms 3, 4, and 5)

Transactions by officers, directors, and 10% owners under Section 16, often within two business days of the trade. Use it to answer "are the people who run this company buying or selling their own stock?" It is the most timely of the three. The three families are complementary: a 13D activist building a stake, the 13F managers reacting next quarter, and the insiders trading around it.

Point-in-time ownership without lookahead bias

Every row carries the date its filing was reported, which is what keeps an ownership backtest honest. A position is not knowable to the market until its 13D or 13G actually hits EDGAR, so a simulation must use the filing date, not the date the stake was acquired or the quarter it describes. Joining ownership to prices on anything earlier leaks the future into the test.

Because the history endpoint preserves each filing with its own date and never overwrites a superseded one, you can reconstruct exactly what an investor could have known on any past day: which holders had crossed 5%, who was passive, and who had just flipped to a 13D. That is the same point-in-time discipline StockFit applies to financials, covered in depth in our point-in-time data for backtesting guide. If you are evaluating a beneficial ownership API for research, the filing-date fidelity matters more than the field count.

The beneficial ownership endpoints are on the Stock and Professional plans; the raw 13D and 13G filing trail on /api/filings is free. You can get a token from the StockFit dashboard and call it immediately, no credit card required to sign up. This is data, not investment advice.

FAQ

What is the difference between Schedule 13D and Schedule 13G?

Both disclose beneficial ownership above 5% of a voting class, but the form encodes intent. Schedule 13D is for active investors who intend to influence or control the company (activists, bidders, proxy contests). Schedule 13G is for passive holders with no control intent: index funds, ETFs, and qualified institutional investors. In the StockFit API the filingType field tells you which is which, so you never parse a cover page to classify a holder.

What ownership threshold triggers a 13D or 13G filing?

Acquiring beneficial ownership of more than 5% of a voting class of a registered equity security triggers the obligation. An investor with control intent files Schedule 13D; a passive holder or qualified institutional investor files Schedule 13G. The 2024 rules shortened the initial 13D deadline to 5 business days after crossing the threshold, with amendments due within 2 business days of a material change.

How do I get SEC 13D and 13G beneficial ownership data as JSON?

Call the StockFit /api/ownership/beneficial-owners endpoint with a ticker. It returns every Schedule 13D and 13G filer for that company as JSON, each row carrying the reporting person, filing type, percent of class, aggregate shares owned, report date, and the SEC accession number and filing URL. One call per ticker, no scraping of EDGAR cover pages.

How can I detect when an investor switches from 13G to 13D?

Use the /api/ownership/beneficial-owners/history endpoint, which returns every filing per reporting person over time rather than only the latest. For a given holder, a Schedule 13G followed by a later Schedule 13D is the passive-to-activist switch. Each row carries its own filing date, so the timeline is exact and the prior passive filing is not overwritten.

Is beneficial ownership (13D/13G) the same as 13F institutional ownership?

No. Schedule 13D and 13G disclose concentrated stakes above 5% with passive-or-activist intent attached, filed when the position is taken and amended on changes. Form 13F-HR is a quarterly snapshot of all positions held by institutional managers with over $100M under management, broader and lower per-line, and it lags up to 45 days after quarter end. Use 13D/13G for strategic 5% holders, 13F for the wider institutional book.

Does the API include the SEC accession number for each filing?

Yes. Every beneficial ownership row carries the accessionNumber and a filingUrl pointing at the exact SEC document on EDGAR. That is the audit trail: any percent of class or share count can be traced back to its source filing, which a normalized ownership table from a third-party vendor cannot do.

How current is the 13D/13G data after the 2023 SEC deadline changes?

The 2023 Modernization of Beneficial Ownership Reporting (effective in 2024) shortened the initial Schedule 13D deadline to 5 business days and 13D amendments to 2 business days, and required the schedules to be filed in a structured, machine-readable format. StockFit ingests filings as they hit EDGAR and returns the resolved current position per holder, so the data reflects the faster post-2024 cadence and handles both the new structured cover pages and the legacy free-text ones.