CoStar Group, Inc.

The full register, from 13F filings

The Register tab above is hand research: a dozen holders, each traced to the filing it came from. This asks the same question of the whole market for the quarter ended 31-mar-2026, where 778 managers reported a position. Broad where the research is deep, and shallow in the ways a 13F always is.

Built from 13F filings, which report US listed, long, US custodied positions only. A register from this source is a floor rather than a level: a holder's true position can be far larger, as BlackRock's ASML stake shows at 1.28m shares in a 13F against 26.3m in its 13G/A. Holdings held through derivatives, outside US custody, or below a manager's reporting obligation do not appear. Where a holder is marked as a family, its total sums several separate filing entities and describes something no single filing describes; the constituent entities and their share counts are listed so the total can be checked. That roll-up can legitimately exceed the family's own Schedule 13G, because a 13G is filed by one legal entity: Vanguard reports Alphabet through ten advisory entities, and The Vanguard Group Inc itself reported zero after its January 2026 disaggregation.

What a reader needs to know to read these numbers

• Holdings side is legitimately empty. CoStar has completed full acquisitions of both companies where it previously held minority stakes: Matterport, LLC (acquisition completed February 2025) and Domain Holdings Australia Pty Limited (acquisition completed 27 August 2025, for a combined Matterport + Domain purchase price of approximately $3.9 billion per the FY2025 10-K). Both are now wholly owned subsidiaries, confirmed by name in Exhibit 21.1 of the FY2025 10-K (filed 26 Feb 2026), which is a bare subsidiary name list with no ownership-percentage column. The Q2 2026 10-Q (period 30 Jun 2026, filed 29 Jul 2026) confirms the prior-year unrealized gains on 'equity securities of Domain' ($9m and $12m, three and six months ended 30 Jun 2025) relate to the period BEFORE the August 2025 acquisition, when CoStar briefly held Domain as a minority equity-method-adjacent position ahead of taking it private; that position no longer exists as of this filing. Visual Lease, LLC (acquired 1 Nov 2024) and OnTheMarket Ltd (acquired 2023) are likewise wholly owned subsidiaries per Exhibit 21.1. Searched the Q2 2026 10-Q and FY2025 10-K (including Exhibit 21.1) for 'equity method', 'equity investment', 'equity securities', 'non-marketable', 'cost method', 'joint venture', 'Domain Holdings', 'unrealized gain', 'investment in': no remaining minority stake, joint venture, or private-company investment of any kind was found. Also checked SEC EDGAR for SC 13D/13D-A/13G/13G-A filed BY CoStar against another issuer: none found (only filings AGAINST CoStar's own stock, by its holders, exist).
• Self-gate computed from this final file: 18 register rows. Members counted at full value, the officers/directors aggregate reduced only by the one member that rolls into it (Florance): 16 institutional rows sum to 238,628,892 shares, plus Florance 3,044,568 shares (full value, a member), plus the aggregate's residual (4,838,145 minus Florance's 3,044,568 = 1,793,577 shares) = 243,467,037 total shares, against shares_outstanding 405,197,588 = 60.09% of the company. This is above the 55% flag threshold in the brief. Checked for the three usual causes and found none: every institutional row is the same CUSIP 22160N109 common stock read directly from each holder's own Q2 2026 13F-HR (T. Rowe Price's thousands-denominated value was caught and converted, see its own method_note; JPMorgan's 45,000-share OPTION line was identified by CUSIP and excluded), all implied prices cluster tightly around $28.32/share except two disclosed outliers (Geode ~$28.22, JPMorgan ~$29.43, both flagged in their own rows rather than silently absorbed), and no holder appears twice (Vanguard is one family row summing 8 successor entities behind a 13F-NT parent, Capital Group is one family row summing 3 of 6 checked registrants, T. Rowe Price is one row after confirming the second registrant holds zero). The elevated concentration looks like a genuine feature of this stock rather than an error: insider ownership is tiny (the entire 13-person officer/director group holds only 1.18%, no dual-class structure), and CSGP has fallen sharply over the trailing year (52-week range $25.89 to $91.89, last price $33.54 on 19 Aug 2026, up 6.88% intraday), which is exactly the setup that draws concentrated conviction buying from the growth and value managers that dominate this register (Baron/BAMCO, Akre, Polen, Baillie Gifford). Reported here rather than suppressed, per the brief's own guidance (see also data/research/dominos.json, which shipped at 58.66% under the same reasoning).
• The DEF 14A's own 5%-owner table (2026 proxy, Stock Ownership Information) is stale and internally inconsistent with a full family sweep: it lists only two Vanguard sub-entities (Vanguard Portfolio Management 38,292,035 sh / 9.38% and Vanguard Capital Management 31,613,997 sh / 7.74%, no date given for these two) and BlackRock at 31,820,259 sh / 7.79% sourced to a Schedule 13G/A 'as of March 31, 2025', over a year stale by the time of this research. This file uses each entity's own fresh Q2 2026 13F-HR instead, per the brief's explicit guidance to prefer the fresh 13F over a stale 13G quoted in a proxy; the two sets of figures are reconciled here rather than either one being silently overwritten.
• Implied per-share price check: institutional 13F dollar values divide by their share counts to ~$28.32 across nearly every filer checked (Vanguard's 8 entities, BlackRock, BAMCO, all three Capital Group entities, State Street, Baillie Gifford, Akre, Polen, Invesco, Morgan Stanley, Goldman Sachs, Principal, FMR, and T. Rowe Price after the thousands conversion), all dated 30 Jun 2026, a tight independent cross-check that these are all the same instrument at the same date. Geode (~$28.22) and JPMorgan (~$29.43) deviate slightly; flagged in their own method_notes rather than averaged in or treated as an error.
• Current price used for market_cap_usd is a live intraday quote (Nasdaq API, $33.54, 19 Aug 2026, up 6.88% / +$2.16 on the day) multiplied by the 27 Jul 2026 cover-page share count; the two dates do not match exactly (about three weeks apart) because no single filing carries both a current price and a current share count. This is disclosed rather than treated as precise. Note the large single-day move and the wide 52-week range ($25.89 to $91.89) mean market cap is unusually sensitive to the exact date used here.