UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington D.C. 20549

FORM 10-D

ASSET BACKED ISSUER
DISTRIBUTION REPORT PURSUANT TO SECTION 13 OR 15(d) OF
THE SECURITIES EXCHANGE ACT OF 1934

For the monthly distribution period from: August 16, 2025 to September 17, 2025

Commission File Number of issuing entity: 333-227081-06

Central Index Key Number of issuing entity: 0001832873

CSAIL 2021-C20 Commercial Mortgage Trust
(Exact name of issuing entity as specified in its charter)

Commission File Number of depositor: 333-227081

Central Index Key Number of depositor: 0001654060

Credit Suisse Commercial Mortgage Securities Corp.
(Exact name of depositor as specified in its charter)

Central Index Key Number of sponsor (if applicable): 0001767304

3650 REIT Loan Funding 1 LLC
(Exact name of sponsor as specified in its charter)

Central Index Key Number of sponsor (if applicable): 0001628601

Column Financial, Inc.
(Exact name of sponsor as specified in its charter)

Central Index Key Number of sponsor (if applicable): 0001685185

UBS AG
(Exact name of sponsor as specified in its charter)

Central Index Key Number of sponsor (if applicable): 0001541294

German American Capital Corporation
(Exact name of sponsor as specified in its charter)

Nader Attalla (212) 325-4217
(Name and telephone number, including area code, of the person to contact in connection with this filing)

New York
(State or other jurisdiction of incorporation or organization of the issuing entity)

35-7287108
38-4169430
38-4169431
(I.R.S. Employer Identification No.)

c/o Computershare Trust Company, N.A., as agent for
Wells Fargo Bank, National Association
9062 Old Annapolis Road
Columbia, MD 21045
(Address of principal executive offices of the issuing entity) (Zip Code)

(667) 786-1992
(Telephone number, including area code)

Not Applicable
(Former name, former address, if changed since last report)

Registered/reporting pursuant to (check one)

Title of Class	Section 12(b)	Section 12(g)	Section 15(d)	Name of Exchange (If Section 12(b))
A-1			X
A-2			X
A-3			X
A-SB			X
X-A			X
X-B			X
A-S			X
B			X
C			X

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes X No

Part I - DISTRIBUTION INFORMATION

Item 1. Distribution and Pool Performance Information.

On September 17, 2025 a distribution was made to holders of the certificates issued by CSAIL 2021-C20 Commercial Mortgage Trust.

The distribution report is attached as an Exhibit to this Form 10-D, please see Item 10(b), Exhibit 99.1 for the related information.

No assets securitized by Credit Suisse Commercial Mortgage Securities Corp. (the "Depositor") and held by CSAIL 2021-C20 Commercial Mortgage Trust were the subject of a demand to repurchase for breach of the representations and warranties contained in the underlying transaction documents during the distribution period from August 16, 2025 to September 17, 2025.

The Depositor has filed a Form ABS-15G pursuant to Rule 15Ga-1 under the Securities Exchange Act of 1934 on February 7, 2025. The CIK number of the Depositor is 0001654060.

3650 REIT Loan Funding 1 LLC (“3650 REIT”), one of the sponsors, has filed a Form ABS-15G pursuant to Rule 15Ga-1 under the Securities Exchange Act of 1934 on February 14, 2025. The CIK number of 3650 REIT is 0001767304.

Column Financial, Inc. ("Column"), one of the sponsors, has filed a Form ABS-15G pursuant to Rule 15Ga-1 under the Securities Exchange Act of 1934 on February 7, 2025. The CIK number of Column is 0001628601.

UBS AG, one of the sponsors, has filed a Form ABS-15G pursuant to Rule 15Ga-1 under the Securities Exchange Act of 1934 on February 12, 2025. The CIK number of UBS AG is 0001685185.

German American Capital Corporation ("GACC"), one of the sponsors, has filed a Form ABS-15G pursuant to Rule 15Ga-1 under the Securities Exchange Act of 1934 on February 13, 2025. The CIK number of GACC is 0001541294.

Item 1A. Asset-Level Information.

ABS Asset Data File (filed as Exhibit 102 to the registrant's Form ABS-EE filed on September 29, 2025 under Commission File No. 333-227081-06 and incorporated by reference herein).

ABS Asset Related Document (filed as Exhibit 103 to the registrant's Form ABS-EE filed on September 29, 2025 under Commission File No. 333-227081-06 and incorporated by reference herein).

Part II - OTHER INFORMATION

Item 9. Other Information.

Midland Loan Services, A Division of PNC Bank, National Association, in its capacity as Master Servicer for CSAIL 2021-C20 Commercial Mortgage Trust, affirms the following amounts in the respective accounts:

Collection Account
Prior Distribution Date	08/15/2025	$7,000.00
Current Distribution Date	09/17/2025	$7,000.00

REO Account
Prior Distribution Date	08/15/2025	$0.00
Current Distribution Date	09/17/2025	$0.00

Computershare Trust Company, N.A., as agent for Wells Fargo Bank, N.A., in its capacity as Certificate Administrator for CSAIL 2021-C20 Commercial Mortgage Trust, affirms the following amounts in the respective accounts:

Distribution Account
Prior Distribution Date	08/15/2025	$6,209.65
Current Distribution Date	09/17/2025	$6,207.25

Interest Reserve Account
Prior Distribution Date	08/15/2025	$0.00
Current Distribution Date	09/17/2025	$0.00

Gain-on-Sale Reserve Account
Prior Distribution Date	08/15/2025	$0.00
Current Distribution Date	09/17/2025	$0.00

Item 10. Exhibits.

(a) The following is a list of documents filed as part of this Report on Form 10-D:

(99.1) Monthly report distributed to holders of the certificates issued by CSAIL 2021-C20 Commercial Mortgage Trust, relating to the September 17, 2025 distribution.

(102) ABS Asset Data File (filed as Exhibit 102 to the registrant's Form ABS-EE filed on September 29, 2025 under Commission File No. 333-227081-06 and incorporated by reference herein).

(103) ABS Asset Related Document (filed as Exhibit 103 to the registrant's Form ABS-EE filed on September 29, 2025 under Commission File No. 333-227081-06 and incorporated by reference herein).

(b) The exhibits required to be filed by the Registrant pursuant to this Form are listed above.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

Credit Suisse Commercial Mortgage Securities Corp.
(Depositor)

/s/ Dmitriy Kogan
Dmitriy Kogan, Authorized Signatory

Date: September 29, 2025

/s/ Russell Moy
Russell Moy, Authorized Signatory

Date: September 29, 2025

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington D.C. 20549

FORM 10-D

ASSET BACKED ISSUER DISTRIBUTION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

Registered/reporting pursuant to (check one)

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington D.C. 20549

ASSET BACKED ISSUER
DISTRIBUTION REPORT PURSUANT TO SECTION 13 OR 15(d) OF
THE SECURITIES EXCHANGE ACT OF 1934

CSAIL 2021-C20 Commercial Mortgage Trust 10-D