Exhibit 99.1

MONTHLY SERVICER'S CERTIFICATE

CARMAX BUSINESS SERVICES, LLC

CARMAX AUTO OWNER TRUST

SERIES 2021-4

Collection Period

09/01/25-09/30/25

Determination Date

10/9/2025

Distribution Date

10/15/2025

Additional information, including defined terms, can be found in the prospectus on the SEC's EDGAR system (http://www.sec.gov) under File No. 333-228379-12.


Pool Balance
1.	Pool Balance on the close of the last day of the preceding Collection Period			$	177,166,350.75
2.	Collections allocable to Principal			$	12,039,234.44
3.	Purchase Amount allocable to Principal			$	0.00
4.	Defaulted Receivables			$	789,953.06
5.	Pool Balance on the close of the last day of the related Collection Period			$	164,337,163.25
	(Ln1 - Ln2 - Ln3 - Ln4)
6.	Total number of Receivables outstanding on the close of the last day of the related Collection Period			24,941
7.	Initial Pool Balance			$	1,403,509,094.50
		Beginning of Period		End of Period
8.	Note Balances
	a. Class A-1 Note Balance	$	0.00	$	0.00
	b. Class A-2a Note Balance	$	0.00	$	0.00
	c. Class A-2b Floating Rate Note Balance	$	0.00	$	0.00
	d. Class A-3 Note Balance	$	0.00	$	0.00
	e. Class A-4 Note Balance	$	99,267,578.01	$	86,438,390.51
	f. Class B Note Balance	$	23,860,000.00	$	23,860,000.00
	g. Class C Note Balance	$	32,980,000.00	$	32,980,000.00
	h. Class D Note Balance	$	17,550,000.00	$	17,550,000.00
	i. Note Balance (sum a - h)	$	173,657,578.01	$	160,828,390.51
9.	Pool Factors
	a. Class A-1 Note Pool Factor	0.0000000		0.0000000
	b. Class A-2a Note Pool Factor	0.0000000		0.0000000
	c. Class A-2b Floating Rate Note Pool Factor	0.0000000		0.0000000
	d. Class A-3 Note Pool Factor	0.0000000		0.0000000
	e. Class A-4 Note Pool Factor	0.7631271		0.6645018
	f. Class B Note Pool Factor	1.0000000		1.0000000
	g. Class C Note Pool Factor	1.0000000		1.0000000
	h. Class D Note Pool Factor	1.0000000		1.0000000
	i. Note Pool Factor	0.1240411		0.1148774
10.	Overcollateralization Target Amount			$	3,508,772.74
11.	Current overcollateralization amount (Pool Balance - Note Balance)			$	3,508,772.74
12.	Weighted Average Coupon			9.06		%
13.	Weighted Average Original Term	months		68.79
14.	Weighted Average Remaining Term	months		19.44
15.	Applicable reference rate for the interest period ending 10/14/2025			N/A
16.	Note Rate applicable to the Class A-2b notes for the interest period ending 10/14/2025			N/A
Collections
17.	Finance Charges:
	a. Collections allocable to Finance Charge			$	1,354,392.98
	b. Liquidation Proceeds allocable to Finance Charge			$	2,638.65
	c. Purchase Amount allocable to Finance Charge			$	0.00
	d. Available Finance Charge Collections (sum a - c)			$	1,357,031.63
18.	Principal:
	a. Collections allocable to Principal			$	12,039,234.44
	b. Liquidation Proceeds allocable to Principal			$	395,046.90
	c. Purchase Amount allocable to Principal			$	0.00
	d. Available Principal Collections (sum a - c)			$	12,434,281.34
19.	Total Finance Charge and Principal Collections (17d + 18d)			$	13,791,312.97
20.	Interest Income from Collection Account			$	38,058.84
21.	Simple Interest Advances			$	0.00
22.	Available Collections (Ln19 + 20 + 21)			$	13,829,371.81


Available Funds
23.	Available Collections	$	13,829,371.81
24.	Reserve Account Draw Amount	$	0.00
25.	Available Funds	$	13,829,371.81
Application of Available Funds
26.	Servicing Fee	0.15		%
	a. Monthly Servicing Fee	$	147,638.63
	b. Amount Unpaid from Prior Months	$	0.00
	c. Amount Paid	$	147,638.63
	d. Shortfall Amount (a + b - c)	$	0.00
27.	Unreimbursed Servicer Advances	$	0.00
28.	Successor Servicer and Asset Representations Reviewer Unpaid Expenses and Indemnity Amounts
	a. Successor Servicer Unpaid Transition Expenses and Indemnity Amounts (Capped at $175,000 annually)	$	0.00
	b. Successor Servicer Amount Paid	$	0.00
	c. Successor Servicer Shortfall Amount (a - b)	$	0.00
	d. Asset Representations Reviewer Fees, Expenses and Indemnity Amounts (Capped at $175,000 annually)	$	0.00
	e. Asset Representations Reviewer Amount Paid	$	0.00
	f. Asset Representations Reviewer Shortfall Amount (d - e)	$	0.00
29.	Class A Noteholder Interest Amounts
	a. Class A-1 Monthly Interest	$	0.00
	b. Additional Note Interest related to Class A-1 Monthly Interest	$	0.00
	c. Interest Due on Additional Note Interest related to Class A-1 Monthly Interest	$	0.00
	d. Total Class A-1 Note Interest (sum a - c)	$	0.00
	e. Class A-2a Monthly Interest	$	—
	f. Additional Note Interest related to Class A-2a Monthly Interest	$	0.00
	g. Interest Due on Additional Note Interest related to Class A-2a Monthly Interest	$	0.00
	h. Total Class A-2a Note Interest (sum e - g)	$	—
	i. Class A-2b Monthly Interest	$	—
	j. Additional Note Interest related to Class A-2b Monthly Interest	$	0.00
	k. Interest Due on Additional Note Interest related to Class A-2b Monthly Interest	$	0.00
	l. Total Class A-2b Note Interest (sum i - k)	$	—
	m. Class A-3 Monthly Interest	$	—
	n. Additional Note Interest related to Class A-3 Monthly Interest	$	0.00
	o. Interest Due on Additional Note Interest related to Class A-3 Monthly Interest	$	0.00
	p. Total Class A-3 Note Interest (sum m - o)	$	—
	q. Class A-4 Monthly Interest	$	67,832.84
	r. Additional Note Interest related to Class A-4 Monthly Interest	$	0.00
	r. Additional Note Interest related to Class A-4 Monthly Interest	$	0.00
	t. Total Class A-4 Note Interest (sum q - s)	$	67,832.84
30.	Priority Principal Distributable Amount	$	0.00
31.	Class B Noteholder Interest Amount
	a. Class B Monthly Interest	$	20,678.67
	b. Additional Note Interest related to Class B Monthly Interest	$	0.00
	c. Interest Due on Additional Note Interest related to Class B Monthly Interest	$	0.00
	d. Total Class B Note Interest (sum a - c)	$	20,678.67
32.	Secondary Principal Distributable Amount	$	0.00
33.	Class C Noteholder Interest Amount
	a. Class C Monthly Interest	$	37,927.00
	b. Additional Note Interest related to Class C Monthly Interest	$	0.00
	c. Interest Due on Additional Note Interest related to Class C Monthly Interest	$	0.00
	d. Total Class C Note Interest (sum a - c)	$	37,927.00
34.	Tertiary Principal Distributable Amount	$	0.00
35.	Class D Noteholder Interest Amount
	a. Class D Monthly Interest	$	21,645.00
	b. Additional Note Interest related to Class D Monthly Interest	$	0.00
	c. Interest Due on Additional Note Interest related to Class D Monthly Interest	$	0.00
	d. Total Class D Note Interest (sum a - c)	$	21,645.00


36.	Quaternary Principal Distributable Amount	$	9,320,414.76
37.	Required Payment Amount (Ln 26 + Ln 28 + (sum of Ln 29 through Ln 36))	$	9,616,136.90
38.	Reserve Account Deficiency	$	0.00
39.	Regular Principal Distributable Amount	$	3,508,772.74
40.	Remaining Unpaid Servicer Transition Expenses and Additional Servicing Fees, if any	$	0.00
41.	Remaining Unpaid Trustee and Asset Representations Reviewer Fees, Expenses and Indemnity Amounts, if any
	a. Remaining Unpaid Trustee Fees, Expenses and Indemnity Amounts	$	0.00
	b. Remaining Unpaid Asset Representations Reviewer Fees, Expenses and Indemnity Amounts	$	0.00
42.	Remaining Unpaid Successor Servicer Indemnity Amounts, if any	$	0.00
Collection Account Activity		0.15		%
43.	Deposits
	a. Total Daily Deposits of Finance Charge Collections	$	1,357,031.63
	b. Total Daily Deposits of Principal Collections	$	12,434,281.34
	c. Withdrawal from Reserve Account	$	0.00
	d. Interest Income	$	38,058.84
	e. Total Deposits to Collection Account (sum a - d)	$	13,829,371.81
44.	Withdrawals
	a. Servicing Fee and Unreimbursed Servicer Advances	$	147,638.63
	b. Successor Servicer Transition Expenses and Indemnity Amounts	$	0.00
	c. Deposit to Note Payment Account for Monthly Note Interest/Principal	$	12,977,271.01
	d. Deposit to Reserve Account	$	0.00
	e. Excess Collections (Deposit to Certificate Payment Account for payment to Certificateholder)	$	704,462.17
	f. Total Withdrawals from Collection Account (sum a - e)	$	13,829,371.81
Note Payment Account Activity
45.	Deposits
	a. Class A-1 Interest Distribution	$	0.00
	b. Class A-2a Interest Distribution	$	0.00
	c. Class A-2b Interest Distribution	$	0.00
	d. Class A-3 Interest Distribution	$	—
	e. Class A-4 Interest Distribution	$	67,832.84
	f. Class B Interest Distribution	$	20,678.67
	g. Class C Interest Distribution	$	37,927.00
	h. Class D Interest Distribution	$	21,645.00
	i. Class A-1 Principal Distribution	$	0.00
	j. Class A-2a Principal Distribution	$	0.00
	k. Class A-2b Principal Distribution	$	0.00
	l. Class A-3 Principal Distribution	$	0.00
	m. Class A-4 Principal Distribution	$	12,829,187.50
	n. Class B Principal Distribution	$	0.00
	o. Class C Principal Distribution	$	0.00
	p. Class D Principal Distribution	$	0.00
	q. Total Deposits to Note Payment Account (sum a - p)	$	12,977,271.01
46.	Withdrawals
	a. Class A-1 Distribution	$	0.00
	b. Class A-2a Distribution	$	0.00
	c. Class A-2b Distribution	$	0.00
	d. Class A-3 Distribution	$	0.00
	e. Class A-4 Distribution	$	12,897,020.34
	f. Class B Distribution	$	20,678.67
	g. Class C Distribution	$	37,927.00
	h. Class D Distribution	$	21,645.00
	i. Total Withdrawals from Note Payment Account (sum a - h)	$	12,977,271.01


Certificate Payment Account Activity
47.	Deposits to Certificate Payment Account from Excess Collections	$	704,462.17
48.	Withdrawals from Certificate Payment Account for Certificateholder Distribution	$	704,462.17
Required Reserve Account Amount		0.15		%
49.	Required Reserve Account Amount (1.00% of Initial Pool Balance)	$	3,508,772.74
Reserve Account Reconciliation
50.	Beginning Balance (as of end of preceding Distribution Date)	$	3,508,772.74
51.	Investment Earnings	$	11,914.78
52.	Reserve Account Draw Amount	$	0.00
53.	Reserve Account Amount (Ln 50 + Ln 51 - Ln 52)	$	3,520,687.52
54.	Deposit from Available Funds (Ln 44d)	$	0.00
55.	If Reserve Account Balance exceeds Required Reserve Account Amount, payment to
	a. the Note Payment Account for the payment of principal to the extent of any unfunded Regular Principal Distribution Amount; and	$	0.00
	b. any Successor Servicer for the payment of any unfunded Transition Costs and Additional Servicing Fee	$	0.00
56.	Payment to Depositor if Reserve Account Balance exceeds Required Reserve Account Amount and to the extent no unfunded amounts described in Ln 55 exist	$	11,914.78
57.	Ending Balance (Ln53 + Ln54 - Ln55 - Ln56)	$	3,508,772.74
58.	Reserve Account Deficiency (Ln50 - Ln57)	$	0.00
Instructions to the Trustee
59.	Amount to be deposited from the Reserve Account into the Collection Account	$	0.00
60.	Amount to be paid to Servicer from the Collection Account	$	147,638.63
61.	Amount to be deposited from the Collection Account into the Note Payment Account	$	12,977,271.01
62.	Amount to be deposited from the Collection Account into the Certificate Payment Account	$	704,462.17
63.	Amount to be deposited from the Collection Account into the Reserve Account	$	0.00
64.	Amount to be deposited from the Reserve Account, if Reserve Account Balance exceeds Required Reserve Account Amount, into
	a. the Note Payment Account for any unfunded Regular Principal Distributable Amount	$	0.00
	b. the Depositor, if no unfunded Regular Principal distributable amount exists	$	11,914.78
65.	Amount to be paid to Class A-1 Noteholders from the Note Payment Account	$	0.00
66.	Amount to be paid to Class A-2a Noteholders from the Note Payment Account	$	0.00
67.	Amount to be paid to Class A-2b Noteholders from the Note Payment Account	$	0.00
68.	Amount to be paid to Class A-3 Noteholders from the Note Payment Account	$	0.00
69.	Amount to be paid to Class A-4 Noteholders from the Note Payment Account	$	12,897,020.34
70.	Amount to be paid to Class B Noteholders from the Note Payment Account	$	20,678.67
71.	Amount to be paid to Class C Noteholders from the Note Payment Account	$	37,927.00
72.	Amount to be paid to Class D Noteholders from the Note Payment Account	$	21,645.00
73.	Amount to be paid to Certificateholders from the Certificate Payment Account with respect to Excess Collections	$	704,462.17


Delinquency Activity
		Number of Loans	Principal Balance
74.	Delinquency Analysis
	a. 31 to 60 days past due	1,054	$	10,477,346.96
	b. 61 to 90 days past due	604	$	6,830,107.31
	c. 91 to 120 days past due	111	$	1,157,339.58
	d. 121 or more days past due	0	$	0.00
	e. Total Past Due (sum a - d)	1,769	$	18,464,793.85
	f. Delinquent Loans as a percentage of end of period Pool Balance (Ln 74e / Ln 5)		11.2359		%

75.	Has a Delinquency Trigger Event occurred?		No

Loss Activity
		Number of Loans	Principal Balance

76.	Defaulted Receivables (charge-offs)	71	$	789,953.06
77.	Recoveries	242	$	397,685.55
78.	Net Losses (Ln 76 - Ln 77)		$	392,267.51
79.	Ratio of Net Losses to Beginning of Period Pool Balance (Ln 78 / Ln 1)		0.2214		%

Cumulative Loss Activity
		Number of Loans	Principal Balance

80.	Defaulted Receivables (charge-offs)	4,054	$	62,531,461.12
81.	Recoveries	3,345	$	27,532,490.50
82.	Cumulative Net Losses (Ln 80 - Ln 81)		$	34,998,970.62
83.	Ratio of Cumulative Net Losses to Initial Pool Balance (Ln 82 / Ln 7)		2.4937		%
84.	Average Net Loss on Defaulted Receivables		$	8,633.19

Other Servicing Information

85.	Principal Balance of Receivables extended during the Collection Period		$	2,679,302.52
86.	Pool Balance on the close of the last day of the preceding Collection Period		$	177,166,350.75
87.	Ratio of extensions to pool balance (Ln 85 / Ln 86)		1.51		%

IN WITNESS WHEREOF, the undersigned has duly executed this certificate on October 9, 2025.


CARMAX BUSINESS SERVICES, LLC

As Servicer

By:			/s/ Greg Dostich

Name:			Greg Dostich

Title:			Vice President and Treasurer

CarMax Auto Owner Trust 2021-4 10-D