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Sunriver Management LLC — 13F Holdings & Portfolio

CIK 1663900 · latest 13F-HR filed 2026-08-13

Backtest portfolio

Sunriver Management LLC manages $636.8M in 13F-reported U.S. long-equity assets across 21 reported positions as of its 2026-06-30 13F-HR filing. Its largest disclosed positions are ARMK (9.44%), WCN (8.99%), SSNC (7.92%). Quarter over quarter (versus its 2026-03-31 filing) the fund opened 11 new positions and exited 8; 5 existing positions rose in reported value and 4 fell.

AUM is the long-equity portion reported on Form 13F-HR. Excludes short positions, cash, foreign holdings, and non-13F assets. For informational purposes only — not investment advice.

Loading holdings…
AUM
$636.8M

Long-equity book

Holdings
21

Distinct positions

Period
2026-06-30

Filed 2026-08-13

Q/Q Activity
+11 / −8 / ↑5 / ↓4

vs 2026-03-31

Portfolio charts

Latest quarter's book, what changed, and how the portfolio has evolved across filings.

Portfolio map

Q2 26
ARMK9.4% · -24%WCN9.0% · +6%SSNC7.9% · +2%DG6.0% · newFA5.5% · -36%BKNG5.4% · newLII5.3% · newLYV5.0% · +2%CNM4.7% · newWEX4.5% · -1%GPC4.5% · newBOBS4.0% · +6%PFGC3.9% · -36%CAE3.9% · +16%MGRC3.8% · newNSP3.4% · newHURN3.3% · +1%ROAD3.3% · newWAY2.8% · newSOLS2.7% · newKFY1.7% · new

Box size = position value; colour = change in share count vs the prior quarter (green added, red trimmed, blue new). Rows split across managers or share classes are combined. Click a box for the stock.

Sector mix

% of 13F value

Sectors from each company's SIC code; funds and ETFs grouped separately.

Biggest buys and sells

Q1 26 → Q2 26

Estimated from the change in shares held × the quarter-end price, so price moves alone don't count as buying. New and exited positions are included.

13F assets and positions

4 quarters

Total reported 13F value (bars) and number of positions (line) each quarter. Value changes include market moves.

Top positions over time

reported value

The eight largest current positions, valued at each quarter end.

Concentration

top 10 = 62.8%

Cumulative share of the portfolio held in the largest N positions.

Firm Profile & Key People

As of the firm’s regulatory filing dated Mar 30, 2026.

Assets Under Management
$1.20B
Discretionary
$1.20B
Employees
9
Accounts
7
Address
2 SOUND VIEW DRIVE
2ND FLOOR
GREENWICH, CT 06830
Phone
(203) 900-3900
Website
Name Title / Status Ownership Type
COOK, RANDOLPH, WILLETT ControlFOUNDER AND PORTFOLIO MANAGER
since Jun 2015
Less than 5%Individual
STADNYK, JOHN, NMN ControlCHIEF OPERATING OFFICER, CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER
since Jan 2021
Less than 5%Individual
SUNRIVER GLOBAL LP ControlMANAGING MEMBER
since Aug 2015
75% or moreDomestic Entity
COOK, RANDOLPH, WILLETT Control
Indirect owner via SUNRIVER ADVISORS LLC
MANAGING MEMBER
since Jul 2015
75% or moreIndividual
COOK, RANDOLPH, WILLETT Control
Indirect owner via SUNRIVER GLOBAL LP
LIMITED PARTNER
since Jul 2015
75% or moreIndividual
SUNRIVER ADVISORS LLC Control
Indirect owner via SUNRIVER GLOBAL LP
GENERAL PARTNER
since Jun 2015
General partner, trustee or managerDomestic Entity
Ownership & leadership changes · 7 filings with changes since Sep 4, 2015

From the firm’s regulatory filings, newest first. Dates are filing dates: a filing that no longer lists someone does not say when they left.

Mar 30, 2026 filing
  • ChangedSTADNYK, JOHN, NMN · title CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER → CHIEF OPERATING OFFICER, CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER
Mar 26, 2024 filing
  • ChangedCOOK, RANDOLPH, WILLETT · title FOUNDER AND PORTFOLIO MANAGER - REGISTRANT → FOUNDER AND PORTFOLIO MANAGER
  • ChangedSTADNYK, JOHN, NMN · title CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER - REGISTRANT → CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER
  • ChangedSUNRIVER GLOBAL LP · title MANAGING MEMBER - REGISTRANT → MANAGING MEMBER
Jan 7, 2022 filing
  • No longer listedMORGAN, JUSTIN, DAVID · CHIEF OPERATING OFFICER AND CHIEF COMPLIANCE OFFICER - REGISTRANT · Less than 5% · control person · listed since Jun 2015
  • ChangedSTADNYK, JOHN, NMN · title CHIEF FINANCIAL OFFICER - REGISTRANT → CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER - REGISTRANT
Mar 30, 2021 filing
  • AddedSTADNYK, JOHN, NMN · CHIEF FINANCIAL OFFICER - REGISTRANT · Less than 5% · control person
Feb 18, 2020 filing
  • ChangedSUNRIVER ADVISORS LLC · indirect via SUNRIVER GLOBAL LP: ownership 75% or more → General partner, trustee or manager
Mar 30, 2018 filing
  • ChangedCOOK, RANDOLPH, WILLETT · title MANAGING MEMBER - RELYING ADVISER / PRESIDENT AND PORTFOLIO MANAGER - REGISTRANT → FOUNDER AND PORTFOLIO MANAGER - REGISTRANT; ownership 75% or more → Less than 5%
  • ChangedMORGAN, JUSTIN, DAVID · title CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER - REGISTRANT → CHIEF OPERATING OFFICER AND CHIEF COMPLIANCE OFFICER - REGISTRANT
Jan 13, 2016 filing
  • ChangedCOOK, RANDOLPH, WILLETT · title PRESIDENT AND PORTFOLIO MANAGER → MANAGING MEMBER - RELYING ADVISER / PRESIDENT AND PORTFOLIO MANAGER - REGISTRANT; ownership Less than 5% → 75% or more
  • ChangedMORGAN, JUSTIN, DAVID · title CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER → CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER - REGISTRANT
  • ChangedSUNRIVER GLOBAL LP · title MANAGING MEMBER → MANAGING MEMBER - REGISTRANT
Sep 4, 2015 filing (earliest on record)
  • ListedCOOK, RANDOLPH, WILLETT · PRESIDENT AND PORTFOLIO MANAGER · Less than 5% · control person
  • ListedCOOK, RANDOLPH, WILLETT · MANAGING MEMBER · 75% or more · indirect via SUNRIVER ADVISORS LLC · control person
  • ListedCOOK, RANDOLPH, WILLETT · LIMITED PARTNER · 75% or more · indirect via SUNRIVER GLOBAL LP · control person
  • ListedMORGAN, JUSTIN, DAVID · CHIEF FINANCIAL OFFICER AND CHIEF COMPLIANCE OFFICER · Less than 5% · control person
  • ListedSUNRIVER ADVISORS LLC · GENERAL PARTNER · 75% or more · indirect via SUNRIVER GLOBAL LP · control person
  • ListedSUNRIVER GLOBAL LP · MANAGING MEMBER · 75% or more · control person

Quarter-over-quarter changes

Changes in reported position value vs the prior 13F, so price moves count too, not just shares bought or sold.

Sunriver Management LLC Holdings (2026-06-30)

Rows tagged Call or Put are options positions, not stock. Per SEC Form 13F-HR, Value shows the notional value of the underlying (shares covered × underlying price), not the option premium. Shares is the number of underlying shares covered (divide by 100 for contract count).

# Issuer Symbol CUSIP Value Weight Shares Type
1 ARAMARK ARMK 03852U106 $60.1M 9.44% 1,056,474 SH
2 WASTE CONNECTIONS INC WCN 94106B101 $57.3M 8.99% 343,513 SH
3 SS&C TECH HLDGS SSNC 78467J100 $50.5M 7.92% 813,251 SH
4 DOLLAR GEN CORP DG 256677105 $38.3M 6.02% 333,053 SH
5 FIRST ADVANTAGE CORP NEW FA 31846B108 $35.0M 5.50% 1,940,912 SH
6 BOOKING HOLDINGS INC BKNG 09857L108 $34.7M 5.44% 194,470 SH
7 LENNOX INTL INC LII 526107107 $33.8M 5.31% 59,007 SH
8 LIVE NATION ENTERTAINMENT IN LYV 538034109 $32.0M 5.02% 174,743 SH
9 CORE & MAIN INC CNM 21874C102 $29.9M 4.70% 620,017 SH
10 WEX INC WEX 96208T104 $28.6M 4.49% 202,518 SH
11 GENUINE PARTS CO GPC 372460105 $28.5M 4.48% 241,980 SH
12 BOBS DISC FURNITURE INC BOBS 09681N106 $25.6M 4.02% 1,616,590 SH
13 PERFORMANCE FOOD GROUP CO PFGC 71377A103 $24.6M 3.87% 220,456 SH
14 CAE INC CAE 124765108 $24.5M 3.85% 979,193 SH
15 MCGRATH RENTCORP MGRC 580589109 $24.0M 3.78% 198,684 SH
16 INSPERITY INC NSP 45778Q107 $21.4M 3.35% 516,995 SH
17 HURON CONSULTING GROUP INC HURN 447462102 $21.2M 3.34% 235,663 SH
18 CONSTRUCTION PARTNERS INC ROAD 21044C107 $20.8M 3.27% 175,223 SH
19 WAYSTAR HLDG CORP WAY 946784105 $17.6M 2.76% 855,000 SH
20 SOLSTICE ADVANCED MATLS INC SOLS 83443Q103 $17.4M 2.74% 196,879 SH
21 KORN FERRY KFY 500643200 $10.9M 1.71% 163,836 SH
Filing History
Period Filed AUM Holdings Accession
2026-06-30 2026-08-13 $636.8M 21 0001892688-26-000115
2026-03-31 2026-05-14 $591.3M 18 0001892688-26-000072
2025-12-31 2026-02-13 $953.9M 23 0001892688-26-000031
2025-09-30 2025-11-13 $920.0M 21 0001892688-25-000189
Filer Information
Address
2 SOUND VIEW DRIVE
2ND FLOOR
GREENWICH, CT 06830
Phone
(203) 900-3900
Filing Manager
Sunriver Management LLC
GREENWICH, CT
Signatory
John Stadnyk
COO/CFO/CCO