13F vs 13D vs 13G vs Form 4: Who Owns What, Explained

The four forms at a glance

The scale is lopsided. 1,824 managers filed 13Fs for Q1 2026, a position-level dataset of 1.87M holdings representing $53.7T in reported long value. Form 4 is the opposite shape, a continuous drip of small events (51,000+ insider transactions in Arkolith's dataset) where one filing can matter more than a thousand routine ones.

Two lesser-known forms complete the insider family: Form 3 (initial statement of ownership, due within 10 days of becoming an insider) and Form 5 (annual catch-up for Form 4-exempt transactions, due within 45 days of fiscal year end). Parse only Form 4 and gifts or certain grants surface months late, looking like they came from nowhere.

How to read them together

• 13F is your map of institutional positioning, but it's lagged up to 45 days and long-only. (Deep dive: how to read a 13F filing.)
• 13D is the activist alarm: someone took a big stake and wants change, with the plans spelled out in the filing's "purpose of transaction" section.
• 13G is the quieter cousin: a big passive holder, often an index manager whose stake says more about fund flows than conviction.
• Form 4 is the most timely signal: insiders trading their own company within two business days.

The richest picture comes from joining them. Berkshire Hathaway's full portfolio surfaces only quarterly via 13F. But cross 5% of one company and a 13D or 13G appears within days of the event, not the quarter. Cross 10% and the holder becomes a statutory insider of that issuer, so later purchases hit the tape on Form 4 within 2 business days. The market has watched well-known buyers accumulate in near real time, long before the next 13F confirmed the stake. Same money, three disclosure speeds.

Which filing answers which money question?

The useful workflow is rarely "read one form." It is "resolve the entity, fetch the relevant filing family, then compare time windows." Entity resolution is the hard step: names are inconsistent across forms, 13F keys securities by CUSIP while Form 4 keys by issuer, and one fund family may file through several legal entities. That is why the 13F data layer and Form 4 data layer should be treated as connected sources, not separate trivia pages.

Which should you watch?

• Tracking smart-money positioning over time → 13F. Quarter-over-quarter deltas carry more information than levels; a screenable institutional leaderboard is the practical starting view.
• Hunting activist situations → 13D, then its amendments, which tell you whether the holder is adding, trimming, or escalating.
• Watching insider conviction → Form 4, filtered hard. Open-market purchases with the insider's own cash are the cleanest subset; scheduled-plan sales, option exercises, and tax-withholding transactions are mostly noise.

Timing matters too. 13F activity clusters in the final days before each deadline, so 13F signals arrive in bursts four times a year. 13D and Form 4 arrive continuously, which makes them worth polling rather than batch-reading.

Edge cases that break naive parsers

If you wire these filings into an automated workflow, the failure modes are not exotic. They are the defaults.

• Amendments are not appends. A 13F amendment either restates the entire report or adds holdings omitted from the original. Treat every amendment as additive and you double-count the book; treat every one as a replacement and you collapse a quarter down to the late additions. The amendment-type field decides. Form 4 amendments supersede the original; keep both rows and the trade counts twice.
• Options in 13F are not longs. Put and call positions appear as flagged rows reported against the underlying's value. Sum every row into a "long book" and a bearish put renders as the manager's biggest bullish bet. Separate option legs before aggregating.
• 13F is a partial X-ray. No shorts, no cash, no most bonds, and confidential treatment can delay specific positions. A book that looks small or strangely concentrated may simply be mostly invisible.
• Dual filer status is common. A 10% owner files 13D or 13G as a large holder and Form 4 as a statutory insider. Same position, two filing families. Deduplicate by entity and date, not by form, or ownership totals inflate.
• Passive is a status, not a promise. A 13G filer that develops intent to influence must switch to 13D. The switch is often the earliest public sign that a quiet holder has gone active.

API and MCP example

Make the agent fetch filing data instead of guessing. A REST lookup starts with search:

curl -H "Authorization: Bearer YOUR_KEY" \
  "https://arkolith.com/api/v1/search?q=berkshire"

Then resolve the identifier and pull the holdings:

curl -H "Authorization: Bearer YOUR_KEY" \
  "https://arkolith.com/api/v1/funds/{cik}/holdings"

The durable pattern is search, resolve, fetch, compare: resolve the name once, pull its filing-family data, diff across periods rather than summarizing one document. With MCP, the same workflow is exposed as tools the agent calls directly. Use the MCP quickstart when the assistant should decide which lookup to run, or use the 13F API surface when you are wiring the calls yourself.

The important guardrail is citation: a claim like "Fund X owns Y shares" should carry the source filing, filing date, and quarter-end. If one is missing, treat the answer as incomplete. The forms have different "as of" semantics: a 13F position is as of quarter-end, a Form 4 trade as of the transaction date, a 13D stake as of the triggering event. Mix them without timestamps and you confidently describe a portfolio that never existed on any single day.

A practical watchlist rule

Use 13F for breadth and Form 4 for urgency. A new 13F position shows institutional capital moved into a name, but the snapshot can be up to 45 days stale and partly unwound by publication. A recent open-market insider buy shows someone close to the company acted within days, but it is one person and one transaction. When both point the same direction on the same ticker, the name earns deeper research. When a 13D lands on top, accumulation, insider conviction, and stated activist intent are converging, about as loud as public ownership data gets. None of it is a trade signal by itself; it is a prioritization tool for attention.

Frequently asked questions

What's the difference between 13D and 13G?

Both cover stakes above the 5% threshold. 13D is for holders with intent to influence control, due within 5 business days of crossing; 13G is for passive holders on a slower, calendar-based schedule. If a 13G filer develops activist intent it must switch to 13D, and that switch is itself a signal.

What's the difference between 13F and 13D?

A 13F is a quarterly, long-only snapshot of an institution's entire $100M+ book, filed 45 days after quarter-end, so it shows breadth across many names on a lag. A 13D is event-driven: it is triggered the moment any holder crosses a 5% stake with intent to influence control, and must be filed within 5 business days. In short, 13F tells you what a fund holds across its whole portfolio; 13D tells you fast that someone took a large, activist position in one specific company. The same stake can appear in both: the 13D within days of the event, then again in the holder's next quarterly 13F.

What's the difference between 13F and 13G?

A 13F reports an institution's full long book every quarter regardless of any single position's size. A 13G is filed specifically when a holder passes 5% of one company without intent to influence, the passive counterpart to the activist 13D, on a slower calendar-based schedule than 13D's 5-day clock. So 13F is portfolio-wide positioning; 13G flags which holders have crossed the 5% passive-ownership line in a given name. A 13G filer that later develops activist intent must re-file as a 13D.

What's the difference between 13F and Form 4?

13F is institutional and quarterly; Form 4 is individual and near-real-time. A 13F lists a fund's long U.S. equity positions as of quarter-end, up to 45 days stale. A Form 4 reports a single transaction by a corporate insider (officer, director, or 10% owner) within 2 business days of the trade. Use 13F to see which institutions own a stock and how their stake shifted quarter-over-quarter; use Form 4 to catch insiders buying or selling their own company right now. The two are most powerful joined on the same ticker.

Which is the most timely?

Form 4, due within 2 business days of the insider's transaction. A 13D follows within 5 business days of the triggering event. 13F is the most lagged: up to 45 days after quarter-end, describing positions that may already be months old.

Does 13F show short positions?

No. 13F covers long positions in 13(f) securities only: no shorts, no cash, and listed options appear as flagged put or call rows rather than net exposure. A manager that looks fully long on a 13F may be hedged or net short in reality.

Which filing is best for AI-agent workflows?

13F is the best starting point for institutional ownership because it has a repeatable quarterly structure and a large, consistent filer universe. Form 4 is the best near-real-time complement, capturing insider activity within 2 business days. Joining them on a resolved entity beats asking a model to summarize one filing family from memory.

Can a 13F be used as live portfolio data?

No. It is a delayed disclosure: positions can change the day after quarter-end and nothing shows until the next cycle. Use 13F for historical positioning, quarter-over-quarter changes, and manager behavior, never for claiming a fund's live book.

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Arkolith turns SEC ownership filings into clean, sourced, queryable data. Start with the 13F data layer, connect an agent through the MCP quickstart, or get a key.