SEC ownership of COSTAR GROUP, INC.

Top holders, 13D/G large-stake signals, insider positions, and transaction flow tied to CIK 0001057352.

Holder evidence

50

Lead holder

VANGUARD PORTFOLIO MANAGEMENT LLC

13D/G signal

VANGUARD PORTFOLIO MANAGEMENT LLC

Latest evidence

31 Mar 2026

Top shareholders Insider holders Latest transactions
Issuer identity
CIK
0001057352
Symbol
CSGP on Nasdaq
Location
Arlington, VA
Ownership snapshot
SEC evidence mix
13D/G, 13F, and 3/4/5
Lead holder
VANGUARD PORTFOLIO MANAGEMENT LLC
Latest large-stake holder
VANGUARD PORTFOLIO MANAGEMENT LLC
Latest evidence date
31 Mar 2026

Ownership snapshot

Top shareholders of COSTAR GROUP, INC. (13F + 13D/G + 3/4/5)

Grouped by holder across the latest SEC ownership disclosures. Start with comparable ownership when available, then verify the linked 13F, 13D/G, or 3/4/5 evidence.

Lead holder
VANGUARD PORTFOLIO MANAGE...
13D/G signal
VANGUARD PORTFOLIO MANAGE...
Evidence rows
50
Latest as of
31 Mar 2026
13D/G 13F 3/4/5 Lead comparable stake: 9.1% 13D/G row: VANGUARD PORTFOLIO MANAGEMENT LLC Showing 1-8 of 50 holder rows.
Holder Evidence Ownership % Position 12M Net Δ As of
VANGUARD PORTFOLIO MANAGEMENT LLC
13D/G 13F
Vanguard Portfolio Management · Company
13D/G 13F
9.1%
$1,544,700,692
38,292,035 shares
 $0 31 Mar 2026
VANGUARD CAPITAL MANAGEMENT LLC
13D/G 13F
Vanguard Capital Management · Company
13D/G 13F
7.5%
$1,275,308,639
31,613,997 shares
 $0 31 Mar 2026
BlackRock, Inc.
13D/G 13F
Company
13D/G 13F
7.5%
$2,631,535,419
31,820,259 shares
 $0 31 Mar 2025
Louise S. Sams
3/4/5
Director
3/4/5
0%
$986,979
20,409 shares
 +$48,360 06 Mar 2026
Robert W. Musslewhite
3/4/5
Director
3/4/5
0%
$1,600,334
18,277 shares
 — 09 Sep 2025
John W. Hill
3/4/5
Director
3/4/5
0%
$1,252,105
18,231 shares
 -$154,530 13 Nov 2025
Angelique G. Brunner
3/4/5
Director
3/4/5
0%
$890,134
10,166 shares
 — 09 Sep 2025
Rachel C. Glaser
3/4/5
Director
3/4/5
0%
$186,815
4,157 shares
 +$44,940 02 Mar 2026
How to read this table

Rows are grouped by holder and ranked first by SEC-reported ownership % when it is safely comparable, then by disclosed holdings value. — indicates unavailable or non-comparable values; "mixed-class rows" means the latest filing spans non-comparable classes.

Forms 3/4/5 flow

Insider trading overview

Net insider flow leans to selling over the last 12 months. Net value: -$1,091,674.

Buys
$5,994,762
Insiders: 4
Sells
$7,086,436
Insiders: 3
Net
-$1,091,674
Shares: +68,026
Window
Last 12 months
4 rolling buckets
Buy value Sell value
Shares: 149,150 Shares: 81,124
Window (months) Buy shares Sell shares Buy value Sell value Net value
0-3 93,430 0 $3,514,108 $0 +$3,514,108
3-6 55,720 0 $2,480,654 $0 +$2,480,654
6-9 0 4,091 $0 $281,172 -$281,172
9-12 0 77,033 $0 $6,805,264 -$6,805,264

Reporting owners

Insider holders from Forms 3/4/5

Showing 1-20 of 21 reporting-owner rows connected to COSTAR GROUP, INC.. Open a relationship link for the CIK-to-CIK filing trail.

Rows
21
Lead holder
Michael R. Klein
Net 12M change
-$1,091,673
Latest report
01 May 2026
Name Relationship Holdings Value Past Year Net Change Change % Valuation Report Date
Michael R. Klein Director $148,608,311 Mixed 10 Dec 2024
Andrew C. Florance President and CEO, Director $61,713,025 +$4,994,863 +8.8% Filing P/S 01 May 2026
Wheeler Scott T. Chief Financial Officer $28,627,417 Mixed 26 Apr 2024
Christopher J. Nassetta Director $22,164,729 Mixed 27 Nov 2024
Frank Simuro Chief Technology Officer $18,652,095 Mixed 15 Mar 2026
Frederick G. Saint President, Marketplaces $12,685,645 -$5,709,900 -31% Filing P/S 01 Mar 2026
Michael J. Glosserman Director $8,530,163 Mixed 30 Oct 2023
Lisa Ruggles Senior VP, Global Operations $7,871,175 Mixed 15 Mar 2026
Christian M. Lown Chief Financial Officer $6,474,417 Mixed 10 Mar 2026
Gene Boxer General Counsel and Secretary $4,295,835 Mixed 15 Mar 2026
Michael J. Desmarais Chief Human Resources Officer $3,947,625 Mixed 15 Mar 2026
Robert W. Musslewhite Director $1,600,334 Mixed 09 Sep 2025
Laura Cox Kaplan Director $1,393,984 Mixed 17 Jul 2024
John W. Hill Director $1,252,105 -$154,530 -11% Filing P/S 13 Nov 2025
Cynthia Cammett Cann Chief Accounting Officer $1,131,660 -$315,406 -22% Mixed 15 Mar 2026
Louise S. Sams Director $986,979 +$48,360 +5.2% Filing P/S 06 Mar 2026
Angelique G. Brunner Director $890,134 Mixed 09 Sep 2025
John L. Berisford Director $260,315 Mixed 09 Sep 2025
Christine M. McCarthy Director $260,315 Mixed 09 Sep 2025
Rachel C. Glaser Director $186,815 +$44,940 +32% Filing P/S 02 Mar 2026

Recent insider transactions for COSTAR GROUP, INC.

Showing up to 300 most recent insider transactions from the last 12 months.

Insider Symbol Class Transaction % Reported value Reported price Shares Shares owned Date Ownership
Andrew C. Florance CSGP Common Stock, par value $0.01 per share Purchase 4.33% $2,514,208 $35.20 71,430 1,722,865 01 May 2026 Direct
Gene Boxer CSGP Common Stock, par value $0.01 per share Tax liability -0.5% -482 95,463 15 Mar 2026 Direct
Lisa Ruggles CSGP Common Stock, par value $0.01 per share Tax liability -1.67% -2,977 174,915 15 Mar 2026 Direct
Frank Simuro CSGP Common Stock, par value $0.01 per share Tax liability -2.61% -11,107 414,491 15 Mar 2026 Direct
Michael J. Desmarais CSGP Common Stock, par value $0.01 per share Tax liability -3.17% -2,873 87,725 15 Mar 2026 Direct
Cynthia Cammett Cann CSGP Common Stock, par value $0.01 per share Tax liability -4.53% -1,194 25,148 15 Mar 2026 Direct
Cynthia Cammett Cann CSGP Common Stock, par value $0.01 per share Award 19.9% 4,374 26,342 10 Mar 2026 Direct
Andrew C. Florance CSGP Common Stock, par value $0.01 per share Award 8.13% 124,162 1,651,435 10 Mar 2026 Direct
Christian M. Lown CSGP Common Stock, par value $0.01 per share Award 9.98% 12,268 135,250 10 Mar 2026 Direct
Gene Boxer CSGP Common Stock, par value $0.01 per share Award 29.6% 21,920 95,945 10 Mar 2026 Direct
Michael J. Desmarais CSGP Common Stock, par value $0.01 per share Award 24.2% 17,676 90,598 10 Mar 2026 Direct
Louise S. Sams CSGP Common Stock, par value $0.01 per share Purchase 5.15% $48,360 $48.36 1,000 20,409 06 Mar 2026 Direct
Rachel C. Glaser CSGP Common Stock, par value $0.01 per share Purchase 31.7% $44,940 $44.94 1,000 4,157 02 Mar 2026 Direct
Frederick G. Saint CSGP Common Stock, par value $0.01 per share Purchase 7.7% $906,600 $45.33 20,000 279,851 02 Mar 2026 Direct
Christian M. Lown CSGP Common Stock, par value $0.01 per share Tax liability -5.51% -7,175 122,982 01 Mar 2026 Direct
Andrew C. Florance CSGP Common Stock, par value $0.01 per share Tax liability -3.76% -59,593 1,527,273 01 Mar 2026 Direct
Gene Boxer CSGP Common Stock, par value $0.01 per share Tax liability -5.79% -4,547 74,025 01 Mar 2026 Direct
Michael J. Desmarais CSGP Common Stock, par value $0.01 per share Tax liability -8.01% -6,353 72,922 01 Mar 2026 Direct
Cynthia Cammett Cann CSGP Common Stock, par value $0.01 per share Tax liability -5.93% -1,385 21,968 01 Mar 2026 Direct
Lisa Ruggles CSGP Common Stock, par value $0.01 per share Tax liability -4.78% -8,931 177,892 01 Mar 2026 Direct
Frank Simuro CSGP Common Stock, par value $0.01 per share Tax liability -4.21% -18,702 425,598 01 Mar 2026 Direct
Frederick G. Saint CSGP Common Stock, par value $0.01 per share Tax liability -4.1% -11,096 259,851 01 Mar 2026 Direct
Christian M. Lown CSGP Restricted Stock Units Award 39,652 39,652 27 Feb 2026 Direct
Frederick G. Saint CSGP Restricted Stock Units Award 39,652 39,652 27 Feb 2026 Direct
Andrew C. Florance CSGP Restricted Stock Units Award 83,708 83,708 27 Feb 2026 Direct
Gene Boxer CSGP Restricted Stock Units Award 26,888 26,888 27 Feb 2026 Direct
Michael J. Desmarais CSGP Restricted Stock Units Award 17,926 17,926 27 Feb 2026 Direct
Cynthia Cammett Cann CSGP Restricted Stock Units Award 6,834 6,834 27 Feb 2026 Direct
Lisa Ruggles CSGP Restricted Stock Units Award 28,197 28,197 27 Feb 2026 Direct
Frank Simuro CSGP Restricted Stock Units Award 52,869 52,869 27 Feb 2026 Direct
Andrew C. Florance CSGP Common Stock, par value $0.01 per share Purchase 3.64% $2,480,654 $44.52 55,720 1,586,866 27 Feb 2026 Direct
Frank Simuro CSGP Common Stock, par value $0.01 per share Tax liability -0.99% -4,421 444,300 19 Feb 2026 Direct
Frank Simuro CSGP Common Stock, par value $0.01 per share Disposed to Issuer -6.41% -30,727 448,721 19 Feb 2026 Direct
Frederick G. Saint CSGP Common Stock, par value $0.01 per share Tax liability -0.79% -2,149 270,947 19 Feb 2026 Direct
Frederick G. Saint CSGP Common Stock, par value $0.01 per share Disposed to Issuer -6.05% -17,583 273,096 19 Feb 2026 Direct
Andrew C. Florance CSGP Common Stock, par value $0.01 per share Tax liability -1.24% -19,221 1,531,146 19 Feb 2026 Direct
Andrew C. Florance CSGP Common Stock, par value $0.01 per share Disposed to Issuer -6.34% -104,983 1,550,367 19 Feb 2026 Direct
Lisa Ruggles CSGP Common Stock, par value $0.01 per share Tax liability -1.69% -3,219 186,823 19 Feb 2026 Direct
Lisa Ruggles CSGP Common Stock, par value $0.01 per share Disposed to Issuer -8.47% -17,583 190,042 19 Feb 2026 Direct
Frank Simuro CSGP Common Stock, par value $0.01 per share Tax liability -0.86% -4,151 479,448 15 Feb 2026 Direct
Andrew C. Florance CSGP Common Stock, par value $0.01 per share Tax liability -1.05% -17,482 1,655,350 15 Feb 2026 Direct
Lisa Ruggles CSGP Common Stock, par value $0.01 per share Tax liability -1.69% -3,576 207,625 15 Feb 2026 Direct
Frederick G. Saint CSGP Common Stock, par value $0.01 per share Tax liability -0.83% -2,424 290,679 15 Feb 2026 Direct
John W. Hill CSGP Common Stock, par value $0.01 per share Sale -11% $154,530 $68.68 -2,250 18,231 13 Nov 2025 Direct
Cynthia Cammett Cann CSGP Common Stock, par value $0.01 per share Sale -7.35% $126,642 $68.79 -1,841 23,211 13 Nov 2025 Direct
Christine M. McCarthy CSGP Common Stock, par value $0.01 per share Award 2,973 2,973 09 Sep 2025 Direct
Louise S. Sams CSGP Common Stock, par value $0.01 per share Award 20.4% 3,291 19,409 09 Sep 2025 Direct
John L. Berisford CSGP Common Stock, par value $0.01 per share Award 2,973 2,973 09 Sep 2025 Direct
John W. Hill CSGP Common Stock, par value $0.01 per share Award 18.4% 3,177 20,481 09 Sep 2025 Direct
Robert W. Musslewhite CSGP Common Stock, par value $0.01 per share Award 20.6% 3,121 18,277 09 Sep 2025 Direct
* indicates a reported price that failed the local validity check.
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