Filed pursuant to Rule 424(b)(3)
SEC File No. 333-258223

PROSPECTUS SUPPLEMENT NO. 1

(to Prospectus dated April 12, 2022)

ironSource Ltd.

72,661,102 CLASS A ORDINARY SHARES

This prospectus supplement updates, amends and supplements the prospectus contained in our Post-Effective Amendment No. 2 to our Registration Statement on Form F-1, effective as of April 11, 2022 (as supplemented or amended from time to time, the “Prospectus”) (Registration No. 333-258223). Capitalized terms used in this prospectus supplement and not otherwise defined herein have the meanings specified in the Prospectus.

This prospectus supplement is being filed to update, amend and supplement the information included in the Prospectus with information on ironSource’s first quarter 2022 financial results, which is set forth below.

This prospectus supplement is not complete without the Prospectus. This prospectus supplement should be read in conjunction with the Prospectus, which is to be delivered with this prospectus supplement, and is qualified by reference thereto, except to the extent that the information in this prospectus supplement updates or supersedes the information contained in the Prospectus. Please keep this prospectus supplement with your Prospectus for future reference.

Our Class A ordinary shares are listed on the New York Stock Exchange under the symbol “IS.” On May 11, 2022, the closing price for our Class A ordinary shares on the New York Stock Exchange was $3.17 per share.

Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on page 17 of the Prospectus and other risk factors contained in the documents incorporated by reference therein for a discussion of information that should be considered in connection with an investment in our securities.

Neither the Securities and Exchange Commission, the Israeli Securities Authority nor any state securities commission has approved or disapproved of these securities or determined if the Prospectus or this prospectus supplement is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is May 12, 2022.

IRONSOURCE LTD.

CONDENSED CONSOLIDATED BALANCE SHEETS

(U.S. dollars in thousands, except for number of shares and par value)

(Unaudited)

	March 31,		December 31,
	2022		2021
Assets
Current assets:
Cash and cash equivalents	$	441,225	$	778,261
Accounts receivable, net of allowances of $814 and $437 as of March 31, 2022 and December 31, 2021, respectively		267,603		232,049
Other current assets		59,472		42,382
Total current assets		768,300		1,052,692
Long-term restricted cash		3,435		3,495
Deferred tax assets		6,262		2,012
Operating lease right-of-use asset		36,292		34,116
Property, equipment and software, net		28,272		25,131
Investment in equity securities		20,000		20,000
Goodwill		456,354		240,299
Intangible assets, net		197,727		54,221
Other non-current assets		35,479		18,857
Total assets	$	1,552,121	$	1,450,823

IRONSOURCE LTD.

CONDENSED CONSOLIDATED BALANCE SHEETS (continued)

(U.S. dollars in thousands, except for number of shares and par value)

(Unaudited)

	March 31,			December 31,
	2022			2021
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	284,689		$	247,362
Operating lease liabilities		10,082			7,525
Other current liabilities		67,989			53,949
Total current liabilities		362,760			308,836
Deferred tax liabilities		11,335			6,514
Long-term operating lease liabilities		30,296			30,076
Other non-current liabilities		2,375			2,829
Total liabilities		406,766			348,255
Commitments and contingencies
Shareholders’ equity:
Class A and Class B ordinary shares, no par value; 11,500,000,000 (Class A 10,000,000,000 and Class B 1,500,000,000) shares authorized; 1,021,306,573 (Class A 677,342,226 and Class B 343,964,347) and 1,018,468,804 (Class A 652,938,412 and Class B 365,530,392) issued and outstanding at March 31, 2022 and December 31, 2021, respectively		—			—
Treasury shares, at cost, 6,745,955 Class A ordinary shares held at March 31, 2022 and December 31, 2021		(67,460	)		(67,460	)
Additional paid-in capital		1,071,566			1,042,589
Accumulated other comprehensive income		533			495
Retained earnings		140,716			126,944
Total shareholders’ equity		1,145,355			1,102,568
Total liabilities and shareholders’ equity	$	1,552,121		$	1,450,823

IRONSOURCE LTD.

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

(U.S. dollars in thousands, except share and per share amounts)

(Unaudited)

	Three Months Ended March 31,
	2022		2021
Revenue	$	189,665	$	119,713
Cost of revenue		40,087		20,140
Gross profit		149,578		99,573
Operating expenses:
Research and development		34,656		20,410
Sales and marketing		75,289		48,721
General and administrative		22,847		15,547
Total operating expenses		132,792		84,678
Income from operations		16,786		14,895
Financial expenses, net		346		1,029
Income before income taxes		16,440		13,866
Provision for income taxes		2,668		3,622
Net income	$	13,772	$	10,244
Basic net income per ordinary share	$	0.01	$	0.01
Weighted-average ordinary shares outstanding – basic		1,018,117,047		645,295,222
Diluted net income per ordinary share	$	0.01	$	0.01
Weighted-average ordinary shares outstanding – diluted		1,084,682,754		711,685,249

IRONSOURCE LTD.

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS

(U.S. dollars in thousands)

(Unaudited)

	Three Months Ended March 31,
	2022			2021
Cash flows from operating activities
Net income	$	13,772		$	10,244
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		13,735			5,343
Share-based compensation expenses		24,385			16,810
Non-cash lease expense		184			227
Effect of exchange rate changes on cash and cash equivalents and restricted cash		1,317			(1,246	)
Loss on disposal of property and equipment		2			—
Interest accrued and other financial expenses		—			107
Deferred income taxes, net		(3,835	)		(827	)
Changes in operating assets and liabilities, net of effects of businesses acquired:
Accounts receivable		16,470			(851	)
Other current assets		(16,151	)		(14,750	)
Other non-current assets		(17,447	)		(3,297	)
Accounts payable		(4,985	)		(6,657	)
Other current liabilities		(6,595	)		5,851
Other non-current liabilities		(258	)		199
Net cash provided by continuing operating activities		20,594			11,153
Net cash used in discontinued operating activities		—			(5,168	)
Net cash provided by operating activities		20,594			5,985
Cash flows from investing activities
Purchase of property and equipment		(1,382	)		(473	)
Capitalized software development costs		(3,848	)		(3,015	)
Purchase of intangible assets		—			(1,950	)
Acquisitions, net of cash acquired		(353,626	)		(89,340	)
Maturities of short-term deposits		—			17,590
Net cash used in continuing investing activities		(358,856	)		(77,188	)
Net cash (used in) discontinued investing activities		—			—
Net cash used in investing activities		(358,856	)		(77,188	)
Cash flows from financing activities
Repayment of long-term loan		—			(2,500	)
Payments of deferred offering costs		—			(1,060	)
Exercise of options		2,483			297
Net cash provided by (used in) continuing financing activities		2,483			(3,263	)
Net cash provided by (used in) discontinued financing activities		—			—
Net cash provided by (used in) financing activities		2,483			(3,263	)
Effect of exchange rate changes on cash and cash equivalents and restricted cash		(1,317	)		1,246
Net change in cash and cash equivalents and restricted cash		(335,779	)		(74,466	)
Cash and cash equivalents and restricted cash at beginning of period		781,756			203,087
Cash and cash equivalents and restricted cash at end of period	$	444,660		$	129,867