Exhibit 99.1

Santander Drive Auto Receivables Trust 2021-4

Class A-1 0.16802% Asset Backed Notes

Class A-2 0.37% Asset Backed Notes

Class A-3 0.51% Asset Backed Notes

Class B 0.88% Asset Backed Notes

Class C 1.26% Asset Backed Notes

Class D 1.67% Asset Backed Notes

Class E 4.03% Asset Backed Notes

Servicer’s Certificate

This Servicer’s Certificate has been prepared pursuant to Section 4.6 of the Sale and Servicing Agreement among Santander Drive Auto Receivables Trust 2021-4, as Issuer, Santander Consumer USA Inc. as Servicer, Santander Drive Auto Receivables LLC, as Seller, and Citibank, National Association, as Indenture Trustee, dated as of October 27, 2021. Defined terms have the meanings assigned to them in the Sale and Servicing Agreement or in other Transaction Documents.

Collection Period Beginning:	07/01/2025
Collection Period Ending:	07/31/2025
Previous Payment/Close Date:	07/15/2025
Payment Date	08/15/2025
Days of Interest for Period:	31
Days in Collection Period:	31
Months Seasoned:	46

							Original
Purchases	Units		Cut-off Date		Closing Date		Pool Balance
Initial Purchase		89,465		09/30/2021		10/27/2021		2,098,958,577.81
Total		89,465						2,098,958,577.81

I. PRINCIPAL BALANCE CALCULATION
{1} Beginning of period aggregate Principal Balance																					{1}			297,668,973.38
{2} Payments Received																			{2}		13,368,219.81
{3} Repurchased Receivables																			{3}		17,066.07
{4} Defaulted Receivables																			{4}		3,942,774.17
{5} Cram Down Losses and Other Principal Adjustments																			{5}		(37,765.50	)
{6} Other Receivables adjustments																			{6}		—
{7} Total Principal distributable amount																					{7}			17,290,294.55
{8} End of period aggregate Principal Balance																					{8}			280,378,678.83
{9} Pool Factor																					{9}			0.133580
II. NOTE BALANCE CALCULATION
								Class A-1		Class A-2		Class A-3		Class B		Class C		Class D		Class E			Total
{10} Original Note Balance						{10}			222,400,000.00		543,100,000.00		292,370,000.00		288,610,000.00		243,480,000.00		241,380,000.00		131,180,000.00			1,962,520,000.00
{11} Beginning of period Note Balance						{11}			—		—		—		—		—		103,749,352.51		131,180,000.00			234,929,352.51
{12} First Allocation of Principal						{12}			—		—		—		—		—		—		—			—
{13} Second Allocation of Principal						{13}			—		—		—		—		—		—		—			—
{14} Third Allocation of Principal						{14}			—		—		—		—		—		—		—			—
{15} Fourth Allocation of Principal						{15}			—		—		—		—		—		—		—			—
{16} Fifth Allocation of Principal						{16}			—		—		—		—		—		—		—			—
{17} Regular Allocation of Principal						{17}			—		—		—		—		—		15,474,813.63		—			15,474,813.63
{18} Optional Purchase payment						{18}			—		—		—		—		—		—		—			—
{19} End of period Note Balance						{19}			—		—		—		—		—		88,274,538.88		131,180,000.00			219,454,538.88
{20} Note Pool Factors						{20}			—		—		—		—		—		0.365708		1.000000			0.111823
{21} Principal payment per $1,000						{21}			—		—		—		—		—		64.11		—			7.89
III. RECONCILIATION OF COLLECTION ACCOUNT
Available Funds
{22} Principal Payments Received																			{22}		13,368,219.81
{23} Net Liquidation Proceeds																			{23}		2,215,953.52
{24} Principal on Repurchased Receivables																			{24}		17,066.07
{25} Interest on Repurchased Receivables																			{25}		—
{26} Interest collected on Receivables																			{26}		3,384,642.20
{27} Other amounts received																			{27}		17,948.53
{28} Optional Purchase Price																			{28}		—
{29} Reserve Account Excess Amount																			{29}		—
{30} Reserve Account Draw Amount																			{30}		—
{31} Total Available Funds																					{31}			19,003,830.13
Distributions
{32} Indenture Trustee Fee																			{32}		—
{33} Owner Trustee Fee																			{33}		—
{34} Asset Representations Reviewer Fee																			{34}		—
Servicing Fee
	Calculated Fee		Carryover Shortfall		Change from prior period			Total
{35}		744,172.43		—		—			744,172.43										{35}		744,172.43
Class A Accrued Note Interest
	Class		Beginning Note Balance		Interest Rate			Days		Days Basis		Calculated Interest
{36}		Class A-1		—		0.16802	%		31		ACT/360		—						{36}		—
{37}		Class A-2		—		0.37	%		30		30 / 360		—						{37}		—
{38}		Class A-3		—		0.51	%		30		30 / 360		—						{38}		—
Class A Accrued Note Interest
	Class		Carryover Shortfall		Change from prior period			Carryover Shortfall per $1,000
{39}		Class A-1		—		—			—										{39}		—
{40}		Class A-2		—		—			—										{40}		—
{41}		Class A-3		—		—			—										{41}		—
{42} First Allocation of Principal																			{42}		—
Class B Accrued Note Interest
	Class		Beginning Note Balance		Interest Rate			Days		Days Basis		Calculated Interest
{43}		Class B		—		0.88	%		30		30 / 360		—						{43}		—
Class B Accrued Note Interest
	Class		Carryover Shortfall		Change from prior period			Carryover Shortfall per $1,000
{44}		Class B		—		—			—										{44}		—
{45} Second Allocation of Principal																			{45}		—

Class C Accrued Note Interest
	Class	Beginning Note Balance		Interest Rate			Days		Days Basis		Calculated Interest
{46}	Class C		—		1.26	%		30		30 / 360		—				{46}			—
Class C Accrued Note Interest
	Class	Carryover Shortfall		Change from prior period			Carryover Shortfall per $1,000
{47}	Class C		—		—			—								{47}			—
{48} Third Allocation of Principal																{48}			—
Class D Accrued Note Interest
	Class	Beginning Note Balance		Interest Rate			Days		Days Basis		Calculated Interest
{49}	Class D		103,749,352.51		1.67	%		30		30 / 360		144,384.52				{49}			144,384.52
Class D Accrued Note Interest
	Class	Carryover Shortfall		Change from prior period			Carryover Shortfall per $1,000
{50}	Class D		—		—			—								{50}			—
{51} Fourth Allocation of Principal																{51}			—
Class E Accrued Note Interest
	Class	Beginning Note Balance		Interest Rate			Days		Days Basis		Calculated Interest
{52}	Class E		131,180,000.00		4.03	%		30		30 / 360		440,546.17				{52}			440,546.17
Class E Accrued Note Interest
	Class	Carryover Shortfall		Change from prior period			Carryover Shortfall per $1,000
{53}	Class E		—		—			—								{53}			—
{54} Fifth Allocation of Principal																{54}			—
{55} Reserve Account deposit																{55}			—
{56} Regular Allocation of Principal																{56}			15,474,813.63
{57} Optional Purchase Amount																{57}			—
{58} Distribution to Residual Interestholder																{58}			2,199,913.38
{59} Total Distribution Amount																			{59}			19,003,830.13
IV. RECONCILIATION OF RESERVE ACCOUNT
{60} Beginning of period Reserve Account balance													{60}	20,989,585.78
{61} Deposit to Reserve Account													{61}	—
{62} Release from Reserve Account													{62}	—
{63} End of period Reserve Account balance																			{63}			20,989,585.78
{64} Specified Reserve Account Balance (1.00% of the Pool Balance as of the Cut-Off Date)																			{64}			20,989,585.78
{65} Change in Reserve Account balance from prior period																			{65}			—
V. OVERCOLLATERALIZATION
{66} Targeted Overcollateralization equal to the sum of:																			{66}			60,924,139.95
{67} (a) 10.50% of the Principal Balance of the Receivables at the end of the Collection Period and																{67}			29,439,761.28
{68} (b) 1.50% of the Principal Balance of the Receivables as of the Cut-off Date																{68}			31,484,378.67
{69} End of period Principal Balance of the Receivables																			{69}			280,378,678.83
{70} End of period Note Balance																			{70}			219,454,538.88
{71} Overcollateralization amount at the end of the Collection Period																			{71}			60,924,139.95
{72} Overcollateralization % at the end of the Collection Period																			{72}			21.73	%
VI. STATISTICAL DATA
															Original			Previous			Current
{73} Principal Balance of the Receivables														{73}		2,098,958,577.81			297,668,973.38			280,378,678.83
{74} Weighted average coupon of the Receivables														{74}		14.58	%		13.90	%		13.90	%
{75} Weighted average original term of the Receivables														{75}		71.25			71.90			71.93
{76} Weighted average remaining term of the Receivables														{76}		66.74			27.32			26.42
{77} Number of Receivables														{77}		89,465			23,834			23,090
VII. DELINQUENCY
															Units			Dollars			Percentage
Receivables with Scheduled Payment Delinquent
{78} 31-60 days														{78}		2,789			39,456,220.60			14.07	%
{79} 61-90 days														{79}		1,402			20,963,957.97			7.48	%
{80} 91-120 days														{80}		373			5,504,684.38			1.96	%
{81} 121 + days delinquent														{81}		—			—			0.00	%
{82} Total														{82}		4,564			65,924,862.95			23.51	%
{83} Aggregate Principal Balance of 60 Day Delinquent Receivables (all Receivables that are 60 or more days delinquent as of End of Collection Period)																			{83}			28,624,382.90
{84} Delinquency Percentage as of the End of the Collection Period																			{84}			10.21	%
{85} Delinquency Trigger																			{85}			24.00	%
{86} Delinquency Trigger Occurred																			{86}			No
VIII. REPOSSESSION INVENTORY
																		Units			Dollars
{87} Beginning of period Repossessed Inventory																{87}			277			4,626,694.29
{88} Vehicles Repossessed in current period																{88}			237			3,832,136.36
{89} Repossessed vehicles sold in current period																{89}			188			3,155,408.73
{90} Repossessed vehicles reinstated in current period																{90}			43			581,853.64
{91} Repossessed vehicle adjustment in current period																{91}			—			(2,395.38	)
{92} End of period Repossessed Inventory																{92}			283			4,719,172.90

IX. CUMULATIVE NET LOSS RATIO
				Units (a)		Dollars (a)
{93} Receivables becoming Defaulted Receivables during period			{93}		259		3,942,774.17
{94} Cram Down Losses occurring during period			{94}		12		(37,765.50	)
{95} Net Liquidation Proceeds collected during period			{95}		1,206		2,215,953.52
{96} Net losses during period			{96}				1,689,055.15
(a) Unit count represents # instances in period per loan per line item
		Net Loss for Period		Avg. Portfolio Balance (b)		Net Loss Ratio (c)
{97} Current Period Net Loss Ratio	{97}		1,689,055.15		289,023,826.11		0.58	%
{98} Prior Period Net Loss Ratio	{98}		1,234,442.48		305,693,026.57		0.40	%
{99} Second Prior Period Net Loss Ratio	{99}		826,020.81		322,359,451.02		0.26	%
{100} Third Prior Period Net Loss Ratio	{100}		821,962.98		340,060,932.93		0.24	%
{101} Rolling 3 prior month average Net Loss Ratio	{101}						0.30	%
(b) Average Portfolio Balance calculated using (Beginning of Period Aggregate Balance + End of Period Aggregate Balance)/2
(c) Net Loss Ratio calculated using Net Loss for Period/Average Portfolio Balance for Period
{102} Cumulative Net losses since Cut-off Date (beginning of period)					{102}		175,246,578.87
{103} Net losses during period					{103}		1,689,055.15
{104} Other Adjustments					{104}		—
{105} Cumulative Net losses since Cut-off Date (end of period)					{105}		176,935,634.02
{106} Cumulative Net Loss Ratio (Net losses since the Cut-off Date / Pool Balance as of the Cut-off Date)					{106}		8.43	%

IN WITNESS WHEREOF, the undersigned has duly executed and delivered this monthly Statement to Noteholders as dated below.

Santander Consumer USA Inc., as Servicer
By:	/s/ Craig Shmoldas
Name:	Craig Shmoldas
Title:	Senior Vice President
Date:	August 13, 2025