ALTAROCK PARTNERS LP — 13F Holdings & Portfolio
CIK 1631014 · latest 13F-HR filed 2026-08-17
ALTAROCK PARTNERS LP manages $4.24B in 13F-reported U.S. long-equity assets across 8 reported positions as of its 2026-06-30 13F-HR filing. Its largest disclosed positions are AMZN (32.21%), TDG (27.51%), MSFT (20.54%). Quarter over quarter (versus its 2026-03-31 filing) the fund opened 0 new positions and exited 0; 6 existing positions rose in reported value and 2 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.
Long-equity book
Distinct positions
Filed 2026-08-17
vs 2026-03-31
Portfolio charts
Latest quarter's book, what changed, and how the portfolio has evolved across filings.
Portfolio map
Q2 26Box 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 valueSectors from each company's SIC code; funds and ETFs grouped separately.
Biggest buys and sells
Q1 26 → Q2 26Estimated 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 quartersTotal reported 13F value (bars) and number of positions (line) each quarter. Value changes include market moves.
Top positions over time
reported valueThe eight largest current positions, valued at each quarter end.
Concentration
top 10 = 100%Cumulative share of the portfolio held in the largest N positions.
As of the firm’s regulatory filing dated Apr 24, 2026.
SUITE 410
WEST PALM BEACH, FL 33401
| Name | Title / Status | Ownership | Type |
|---|---|---|---|
| BIG MOUND PARTNERS, LLC Control | GENERAL PARTNER since Jan 2024 | Less than 5% | Domestic Entity |
| CABOT, SHANNON, THERIAULT Control | CHIEF COMPLIANCE OFFICER since Sep 2014 | Less than 5% | Individual |
| MASSEY, MARK, THOMAS Control | FOUNDER & CHIEF INVESTMENT OFFICER since Feb 2002 | 75% or more | Individual |
| MASSEY, MARK, THOMAS Control Indirect owner via BIG MOUND PARTNERS, LLC | MANAGING MEMBER since Jan 2024 | 75% or more | Individual |
Ownership & leadership changes · 5 filings with changes since Mar 16, 2012
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.
- ChangedMASSEY, MARK, THOMAS · title CHIEF EXECUTIVE OFFICER → FOUNDER & CHIEF INVESTMENT OFFICER
- No longer listedAbdolmohammadi, Jacob, Yahya · CHIEF FINANCIAL OFFICER · Less than 5% · control person · listed since Mar 2023
- No longer listedMCDONALD, KEVIN, FRANCIS · CHIEF OPERATING OFFICER · Less than 5% · control person · listed since Jan 2019
- AddedBIG MOUND PARTNERS, LLC · GENERAL PARTNER · Less than 5% · control person
- AddedMASSEY, MARK, THOMAS · MANAGING MEMBER · 75% or more · indirect via BIG MOUND PARTNERS, LLC · control person
- ChangedMASSEY, MARK, THOMAS · title MANAGING MEMBER AND PRESIDENT → CHIEF EXECUTIVE OFFICER
- AddedAbdolmohammadi, Jacob, Yahya · CHIEF FINANCIAL OFFICER · Less than 5% · control person
- No longer listedBRADFORD, SCOTT, DOUGLAS · MANAGING MEMBER · 25–50% · control person · listed since May 2002
- AddedMCDONALD, KEVIN, FRANCIS · CHIEF OPERATING OFFICER · Less than 5% · control person
- AddedCABOT, SHANNON, THERIAULT · CHIEF COMPLIANCE OFFICER · Less than 5% · control person
- ChangedBRADFORD, SCOTT, DOUGLAS · title VICE PRESIDENT → MANAGING MEMBER; ownership Less than 5% → 25–50%
- ChangedMASSEY, MARK, THOMAS · title MANAGING PARTNER AND PRESIDENT → MANAGING MEMBER AND PRESIDENT
- ListedBRADFORD, SCOTT, DOUGLAS · VICE PRESIDENT · Less than 5% · control person
- ListedMASSEY, MARK, THOMAS · MANAGING PARTNER AND PRESIDENT · 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.
Top Adds (vs prior quarter)
- MICROSOFT CORP$179.5M +26.0%
- VISA INC-CLASS A SHRS$136.3M +90.4%
- MASTERCARD INC-CLASS A$131.4M +50.3%
- TRANSDIGM GROUP INC$112.9M +10.7%
- ALPHABET INC-CL A$2.5M +20.3%
ALTAROCK PARTNERS LP 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 | AMAZON.COM INC | AMZN | 023135106 | $1.37B | 32.21% | 5,729,972 | SH |
| 2 | TRANSDIGM GROUP INC | TDG | 893641100 | $1.17B | 27.51% | 875,755 | SH |
| 3 | MICROSOFT CORP | MSFT | 594918104 | $870.8M | 20.54% | 2,334,482 | SH |
| 4 | MASTERCARD INC-CLASS A | MA | 57636Q104 | $392.7M | 9.26% | 764,507 | SH |
| 5 | VISA INC-CLASS A SHRS | V | 92826C839 | $287.0M | 6.77% | 836,470 | SH |
| 6 | MOODYS CORP | MCO | 615369105 | $137.1M | 3.23% | 302,624 | SH |
| 7 | ALPHABET INC-CL A | GOOGL | 02079K305 | $15.0M | 0.35% | 41,994 | SH |
| 8 | HILTON WORLDWIDE | HLT | 43300A203 | $5.0M | 0.12% | 15,202 | SH |
| Period | Filed | AUM | Holdings | Accession |
|---|---|---|---|---|
| 2026-06-30 | 2026-08-17 | $4.24B | 8 | 0001104659-26-097527 |
| 2026-03-31 | 2026-05-15 | $4.13B | 8 | 0001104659-26-062170 |
| 2025-12-31 | 2026-02-13 | $5.10B | 8 | 0001104659-26-015359 |
| 2025-09-30 | 2025-11-14 | $5.47B | 9 | 0001104659-25-112002 |
SUITE 410
WEST PALM BEACH, FL 33401