September 24, 2021

RE: Weekly update on the UBS Prime CNAV series of funds.

Dear Investor:

UBS Asset Management is pleased to provide you with this interim holdings report for Master Trust– Prime CNAV Master Fund (the “Master Fund”). Each of the funds in the UBS Prime CNAV series is a “feeder fund” that invests in individual money market securities through the Master Fund. Holdings are as of September 17, 2021. The UBS Prime CNAV series feeder funds are UBS Prime Preferred Fund, UBS Prime Reserves Fund and UBS Prime Investor Fund.

Further information regarding portfolio holdings of the Master Fund is available on a monthly basis and through annual and semiannual reports. To view a copy of the Master Fund’s latest filing, you can visit the US Securities and Exchange Commission's website at http://www.sec.gov.

For more information, contact the UBS Asset Management National Sales Desk at 888-793 8637.

For the funds in the UBS Prime CNAV series, investors should read and carefully consider the investment objectives, risks, charges and expenses before investing. The funds’ prospectuses contain this and other information about the funds. Contact the UBS Asset Management National Sales Desk at 888-793 8637 for a current fund prospectus. An investment in the funds in the UBS Prime CNAV series is only one component of a balanced investment plan.

Investors should note that current and future portfolio holdings are subject to risk. You could lose money by investing in a UBS Prime CNAV series fund. Although a fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. The fund may impose a fee upon sale of your shares or may temporarily suspend your ability to sell shares if the fund's liquidity falls below required minimums because of market conditions or other factors. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The fund's sponsor has no legal obligation to provide financial support to the fund, and you should not expect that the sponsor will provide financial support to the fund at any time.

Not FDIC insured. May lose value. No bank guarantee.

UBS Asset Management (Americas) Inc. UBS Asset Management (US) Inc. is the funds’ distributor. 16-0923

Master Trust—Prime CNAV Master Fund Holdings | September 17, 2021

Holdings and allocations shown are unaudited, and may not be representative of current or future investments. Holdings and allocations may not include the fund's entire investment portfolio, which may change at any time. Fund holdings should not be relied on in making investment decisions and should not be construed as research or investment advice regarding particular securities.

Please note: The fund is actively managed, and its holdings are subject to change.

Percent of Security name Par Maturity date* fund ABN AMRO BANK 100,000,000.000 09/20/2021 3.21 ALBION CAPITAL CORP 30,000,000.000 09/21/2021 0.96 ALBION CAPITAL CORP 16,000,000.000 10/20/2021 0.51 ANZ NATNL INT LMTD 17,000,000.000 11/29/2021 0.55 ANZ NATNL INT LMTD 17,000,000.000 12/21/2021 0.55 ANZ NATNL INT LMTD 10,000,000.000 11/10/2021 0.32 ASB FINANCE LTD. 18,000,000.000 04/06/2022 0.58 ATLANTIC ASSET SECUR 20,000,000.000 10/06/2021 0.64 ATLANTIC ASSET SECUR 20,000,000.000 09/20/2021 0.64 BANK OF AMERICA 65,000,000.000 12/31/2099 2.09 BANK OF AMERICA 25,000,000.000 12/31/2099 0.80 BANK OF MONTREAL- 13,000,000.000 07/13/2022 0.42 BANK OF MONTREAL- 7,000,000.000 07/21/2022 0.22 BANK OF NOVA SCOTIA/THE 20,000,000.000 06/02/2022 0.64 BANK OF NOVA SCOTIA/THE 11,000,000.000 04/07/2022 0.35 BANQUE ET CAISSE 34,000,000.000 03/01/2022 1.09 BARCLAYS BK PLC 29,000,000.000 11/23/2021 0.93 BARCLAYS BK PLC 26,000,000.000 12/14/2021 0.84 BEDFORD ROW FDG CORP 18,000,000.000 11/01/2021 0.58 BNP TRI PARTY CP2 100,000,000.000 09/20/2021 3.21 BNP TRI PARTY CP2 50,000,000.000 09/20/2021 1.61 BPCE 20,000,000.000 10/06/2021 0.64 CAISSE DES DEPOTS ET 20,000,000.000 01/26/2022 0.64 CAN AST + CAN LTD JT 15,000,000.000 10/04/2021 0.48 CANADIAN IMPERIAL BK 25,000,000.000 09/23/2021 0.80

CANADIAN IMPERIAL BK 16,000,000.000 04/04/2022 0.51 COLLATERALIZED CP FLEX 30,000,000.000 10/19/2021 0.96 COLLATERALIZED CP FLEX 23,000,000.000 10/13/2021 0.74 COLLATERALIZED CP FLEX 15,000,000.000 04/08/2022 0.48 COOPERATIEVE CENTRALE 20,000,000.000 12/21/2021 0.64 CORPOERATIVE CENTRALE 13,000,000.000 05/06/2022 0.42 CORPOERATIVE CENTRALE 12,550,000.000 11/29/2021 0.40 CREDIT AGRICOLE CIB 40,000,000.000 09/20/2021 1.29 CREDIT IND ET CM NY 65,000,000.000 09/22/2021 2.09 CREDIT IND ET CM NY 45,000,000.000 09/20/2021 1.45 DBS BANK LTD 18,000,000.000 10/01/2021 0.58 DBS BANK LTD 17,000,000.000 11/18/2021 0.55 DBS BANK LTD 3,000,000.000 10/20/2021 0.10 DEXIA CREDIT LOCAL SA 31,000,000.000 03/17/2022 1.00 DEXIA CREDIT LOCAL SA 22,000,000.000 12/01/2021 0.71 DEXIA CREDIT LOCAL SA 10,000,000.000 11/02/2021 0.32 DZ BANK AG DEUTSCHE -Z 125,000,000.000 09/20/2021 4.02 ERSTE FINANCE LLC 90,000,000.000 09/23/2021 2.89 ERSTE FINANCE LLC 15,000,000.000 09/24/2021 0.48 EVERGREEN JOINT REPO 35,000,000.000 12/31/2099 1.12 FAIRWAY FINANCE CORP 23,000,000.000 11/05/2021 0.74 FAIRWAY FINANCE CORP 15,000,000.000 02/02/2022 0.48 FAIRWAY FINANCE CORP 12,000,000.000 02/24/2022 0.39 FAIRWAY FINANCE CORP 10,000,000.000 10/08/2021 0.32 FIXED INC CLEARING CORP.REPO 107,700,000.000 09/20/2021 3.46 GOLDMAN TRI PARTY REPO 5,500,000.000 09/20/2021 0.18 J.P. MORGAN SECURITIES LLC 30,000,000.000 12/31/2099 0.96 LMA SA LMA AMERICAS 18,000,000.000 11/30/2021 0.58 LMA SA LMA AMERICAS 18,000,000.000 10/07/2021 0.58 LMA SA LMA AMERICAS 15,000,000.000 10/18/2021 0.48 LMA SA LMA AMERICAS 11,000,000.000 02/10/2022 0.35 LMA SA LMA AMERICAS 8,200,000.000 10/08/2021 0.26 MITSUBISHI UFJ TR+BKG 16,000,000.000 11/08/2021 0.51 MITSUBISHI UFJ TR+BKG 16,000,000.000 11/02/2021 0.51 MIZUHO CORP BANK GRAND CAYMAN 98,500,000.000 09/20/2021 3.16 MUFG BK LTD N Y BRH DISC COML 20,000,000.000 10/05/2021 0.64 NATIONAL BK OF CANAD 18,000,000.000 03/25/2022 0.58 NATIONAL BK OF CANAD 17,000,000.000 02/14/2022 0.55

NATIONAL BK OF CANAD 10,000,000.000 05/20/2022 0.32 NATIONWIDE BLDG SOC 50,000,000.000 10/05/2021 1.61 NATIONWIDE BLDG SOC 48,000,000.000 10/06/2021 1.54 NATIXIS NY 20,000,000.000 10/14/2021 0.64 NATL AUSTRALIA BK LT 14,000,000.000 02/16/2022 0.45 NEDERLANDSE WTRSCHBNK 50,000,000.000 09/22/2021 1.61 NEDERLANDSE WTRSCHBNK 25,000,000.000 09/22/2021 0.80 NORDEA BK AB PUBL 15,000,000.000 12/14/2021 0.48 NORINCHUKIN BK 40,000,000.000 11/22/2021 1.29 NORINCHUKIN BK 40,000,000.000 11/05/2021 1.29 NORINCHUKIN BK 10,000,000.000 11/29/2021 0.32 NORINCHUKIN BK 8,000,000.000 02/25/2022 0.26 NRW. BANK 80,000,000.000 09/22/2021 2.57 NRW. BANK 27,000,000.000 09/24/2021 0.87 OLD LINE FUNDING LLC 21,000,000.000 02/23/2022 0.67 OLD LINE FUNDING LLC 20,000,000.000 02/14/2022 0.64 OLD LINE FUNDING LLC 20,000,000.000 02/10/2022 0.64 OLD LINE FUNDING LLC 16,000,000.000 01/11/2022 0.51 OLD LINE FUNDING LLC 15,500,000.000 11/01/2021 0.50 OVERSEA-CHINESE BANKING CORP L 22,000,000.000 10/01/2021 0.71 OVERSEA-CHINESE BANKING CORP L 19,100,000.000 12/08/2021 0.61 ROYAL BK OF CANADA 31,000,000.000 12/16/2021 1.00 SHEFFIELD RECEIVABLE 50,000,000.000 09/20/2021 1.61 SHEFFIELD RECEIVABLE 20,000,000.000 12/13/2021 0.64 SHEFFIELD RECEIVABLE 12,000,000.000 11/15/2021 0.39 SKANDIN ENS BANKEN AG 22,500,000.000 12/10/2021 0.72 SKANDIN ENS BANKEN AG 20,000,000.000 12/20/2021 0.64 SKANDIN ENS BANKEN AG 20,000,000.000 12/09/2021 0.64 SKANDIN ENS BANKEN AG 19,000,000.000 10/05/2021 0.61 STARBIRD FDG. CORP 25,000,000.000 09/20/2021 0.80 SUMITOMO MITSUI BKG CORP 13,000,000.000 10/20/2021 0.42 SUMITOMO MITSUI BKG CORP 10,000,000.000 10/01/2021 0.32 SUMITOMO MITSUI TR BK 40,000,000.000 09/24/2021 1.29 SUMITOMO MITSUI TR BK 22,000,000.000 12/23/2021 0.71 SUMITOMO MITSUI TRUST NY 26,000,000.000 11/17/2021 0.84 SVENSKA HANDLSBNKN A 20,000,000.000 11/09/2021 0.64 SVENSKA HANDLSBNKN A 20,000,000.000 10/06/2021 0.64 SVENSKA HANDLSBNKN A 17,000,000.000 02/18/2022 0.55

SWEDBANK 15,000,000.000 02/23/2022 0.48 THUNDER BAY FNDNG LLC 27,000,000.000 01/10/2022 0.87 THUNDER BAY FNDNG LLC 20,000,000.000 03/04/2022 0.64 THUNDER BAY FNDNG LLC 20,000,000.000 11/01/2021 0.64 THUNDER BAY FNDNG LLC 15,000,000.000 10/18/2021 0.48 TORONTO DOMINION BANK 20,000,000.000 12/16/2021 0.64 TORONTO DOMINION BANK 20,000,000.000 05/05/2022 0.64 TORONTO DOMINION BANK 20,000,000.000 09/21/2021 0.64 TORONTO DOMINION BANK 13,000,000.000 03/21/2022 0.42 UNITED OVERSEAS BK LTD 31,000,000.000 09/27/2021 1.00 UNITED OVERSEAS BK LTD 23,000,000.000 05/03/2022 0.74 UNITED OVERSEAS BK LTD 15,000,000.000 06/01/2022 0.48 VERSAILLES CDS LLC 20,000,000.000 03/01/2022 0.64 VERSAILLES CDS LLC 20,000,000.000 02/04/2022 0.64 VICTORY RECEIVABLES 25,000,000.000 11/02/2021 0.80 WESTPAC BANKING CORP. 20,000,000.000 11/24/2021 0.64

*In the case of certain securities (e.g., variable rate government securities), “deemed maturity” under Rule 2a-7 may be sooner than that indicated above because of the Rule’s maturity shortening provisions.