SECURITIESFORM AND EXCHANGE COMMISSION8-K

SecuritiesItem registered5.02 pursuantDeparture toof Section 12(b)Directors or Certain Officers; Election of theDirectors; Act:Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

IndentureItem and5.07 NotesSubmission of Matters to a Vote of Security Holders.

•Item failure9.01 byFinancial theStatements Companyand to comply with its obligations in respect of any consolidation, merger or sale of assets;Exhibits.

UNITED ~~STATES~~STATESSECURITIES AND EXCHANGE COMMISSIONWASHINGTON, D.C. 20549

~~Washington,~~CURRENT ~~D.C. 20549~~REPORT

~~FORM~~Pursuant ~~8-K~~to Section 13 or 15(d) of the Securities Exchange Act of 1934

~~CURRENT~~Date ~~REPORT~~of Report (Date of earliest event reported): June 10, 2026

~~Pursuant~~SYNDAX toPHARMACEUTICALS, ~~Section 13 or 15(d)~~INC.

(Exact name of ~~the~~Registrant ~~Securities~~as ~~Exchange~~Specified ~~Act~~in ofIts ~~1934~~Charter)

Date of Report (Date of earliest event reported): June 3, 2026


Delaware	001-37708	32-0162505
(State or Other Jurisdiction of Incorporation)	(Commission File Number)	(IRS Employer Identification No.)

730 THIRD AVENUE FLOOR 9
NEW YORK, New York		10017
(Address of Principal Executive Offices)		(Zip Code)

Registrant’s ~~SYNDAX~~Telephone ~~PHARMACEUTICALS~~Number, ~~INC.~~Including Area Code: (781) 419-1400

(~~Exact~~Former ~~name~~Name ofor ~~registrant~~Former asAddress, ~~specified~~if inChanged ~~its~~Since ~~charter~~Last Report)

Delaware		001-37708		32-0162505
(State or other jurisdiction of incorporation)		(Commission File Number)		(IRS Employer Identification No.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

730 Third Avenue, Floor 9 New York, New York		10017
(Address of Principal Executive Offices)		(Zip Code)

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

~~Registrant’s~~☐Soliciting ~~telephone~~material ~~number,~~pursuant ~~including~~to ~~area~~Rule ~~code:~~14a-12 under the Exchange Act (~~781)~~17 ~~419~~CFR 240.14a-~~1400~~12)

~~Not~~☐Pre-commencement ~~Applicable~~communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

~~(Former~~☐Pre-commencement ~~name~~communications orpursuant ~~former~~to ~~address,~~Rule if13e-4(c) ~~changed~~under ~~since~~the ~~last~~Exchange ~~report~~Act (17 CFR 240.13e-4(c))

~~Check~~Securities ~~the~~registered ~~appropriate~~pursuant ~~box below if the Form 8-K filing is intended~~ to ~~simultaneously~~Section ~~satisfy~~12(b) ~~the filing obligation~~ of the ~~registrant under any of the following provisions (see General Instruction A.2. below)~~Act:

☐Title ~~Written~~of ~~communications~~each ~~pursuant~~class toTradingSymbol(s) ~~Rule~~Name ~~425~~of ~~under~~each ~~the~~exchange ~~Securities~~on ~~Act~~which ~~(17~~registered ~~CFR~~Common ~~230.425)~~Stock SNDX The Nasdaq Stock Market LLC

☐Indicate ~~Soliciting~~by ~~material~~check ~~pursuant~~mark towhether the registrant is an emerging growth company as defined in Rule ~~14a~~405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-122 ~~under~~of the Securities Exchange Act ~~(17~~of ~~CFR~~1934 (§ 240.~~14a~~12b-122 of this chapter).

☐Emerging ~~Pre-commencement~~growth ~~communications~~company ~~pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))~~☐

☐If ~~Pre-commencement~~an ~~communications~~emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to ~~Rule~~Section ~~13e-4~~13(ca) ~~under~~of the Exchange Act ~~(17 CFR 240~~.~~13e-4(c))~~ ☐

~~Title~~At ofthe ~~each~~Syndax ~~class~~Pharmaceuticals, ~~TradingSymbol~~Inc. (the “Company”) 2026 Annual Meeting of Stockholders (the “Annual Meeting”), the Company’s stockholders approved the Company’s 2026 Equity Incentive Plan (the “2026 Plan”), ~~Name~~which the Board of ~~each~~Directors ~~exchange~~of the Company (the “Board”) previously approved, subject to stockholder approval at the Annual Meeting. As a result, the 2026 Plan became effective on ~~which~~June ~~registered~~10, ~~Common~~2026. No ~~stock~~further ~~SNDX~~awards ~~The~~will ~~Nasdaq~~be ~~Stock~~granted ~~Market~~under ~~LLC~~the Company’s 2015 Omnibus Incentive Plan (the “2015 Plan”) following its expiration on March 6, 2026.

~~Indicate~~The by2026 ~~check~~Plan ~~mark~~provides ~~whether~~for the ~~registrant~~grant isof anincentive ~~emerging~~stock ~~growth~~options ~~company~~to asemployees, ~~defined~~including inemployees ~~Rule~~of ~~405~~any ofparent ~~the~~or ~~Securities~~subsidiary, ~~Act~~and offor ~~1933~~the ~~(§230.405~~grant of ~~this~~nonstatutory ~~chapter)~~stock oroptions, ~~Rule~~stock ~~12b-2~~appreciation ofrights, ~~the~~restricted ~~Securities~~stock ~~Exchange~~awards, ~~Act~~restricted stock unit awards, performance awards and other forms of ~~1934~~stock ~~(§240.12b-2~~awards to employees, directors, and consultants, including employees and consultants of ~~this~~the ~~chapter)~~Company’s affiliates.

~~Emerging~~The ~~growth~~2026 ~~company ☐~~Plan provides for the reservation of 7,200,000 shares of the Company’s common stock, plus the number of shares that become available for delivery under the 2015 Plan with respect to Existing Awards (as defined below) in accordance with the share recycling provisions described below. If all or any portion of an award granted under the 2015 Plan that is outstanding as of June 10, 2026 (an “Existing Award”), expires or is cancelled, forfeited, exchanged, settled for cash or otherwise terminated without the actual delivery of shares, any shares subject to such Existing Award will again be available for new awards under the 2026 Plan. Any shares withheld or surrendered in payment of any taxes relating to Existing Awards (other than options or stock appreciation rights) will be again available for new awards under the 2026 Plan.

IfAt anthe ~~emerging~~Annual ~~growth~~Meeting, ~~company~~the Company’s stockholders also approved the Company’s 2026 Employee Stock Purchase Plan (the “2026 ESPP”), ~~indicate~~which bythe ~~check~~Board ~~mark~~previously ifapproved, subject to stockholder approval at the ~~registrant~~Annual ~~has~~Meeting. The ~~elected~~2026 ~~not~~ESPP is the successor to ~~use~~the Company’s 2015 Employee Stock Purchase Plan (the ~~extended~~“2015 ~~transition~~ESPP”). The ~~period~~purpose ~~for~~of ~~complying~~the ~~with~~2026 ~~any~~ESPP is to secure and retain the services of new oremployees, ~~revised~~to ~~financial~~retain ~~accounting~~the ~~standards~~services ~~provided~~of ~~pursuant~~existing employees, and to ~~Section 13(~~provide incentives for such individuals to exert maximum efforts toward our success and that of our affiliates. The 2026 ESPP includes two components. One component is designed to allow eligible U.S. employees to purchase Company common stock in a) manner that may qualify for favorable tax treatment under Section 423 of the ~~Exchange~~Code. The ~~Act~~other component permits the grant of purchase rights that do not qualify for such favorable tax treatment in order to allow deviations necessary to permit participation by eligible employees who are foreign nationals or employed outside of the U. ☐S. while complying with applicable foreign laws. The 2026 ESPP has an effective date of June 10, 2026. In adopting the 2026 ESPP, the Board determined that shares available under the 2015 ESPP will not roll over to the 2026 ESPP.

~~Item~~The foregoing descriptions of the 2026 Plan and the 2026 ESPP in this Current Report on Form 8-K do not purport to be a complete description of all provisions of the 2026 Plan and the 2026 ESPP and are qualified in their entirety by reference to the full text of the 2026 Plan, which is filed herewith as Exhibit 10.1, and the full text of the 2026 ESPP, which is filed herewith as Exhibit 10.012, ~~Entry~~each of which is incorporated into athis ~~Material~~Item ~~Agreement~~5.02 by reference.

OnThe ~~June 3,~~Company ~~2026,~~held ~~Syndax~~its ~~Pharmaceuticals,~~Annual ~~Inc.~~Meeting ~~(the~~on ~~“Company”)~~June ~~entered~~10, ~~into~~2026. The ~~privately~~proposals ~~negotiated~~set ~~subscription~~forth ~~agreements~~below ~~(the~~are ~~“Subscription~~described ~~Agreements”)~~in ~~with~~detail ~~certain~~in ~~investors, pursuant to which~~ the Company’s ~~will~~definitive ~~issue~~proxy ~~$250.0 million~~statement ~~aggregate~~filed ~~principal~~with ~~amount~~the ofSecurities ~~2.25%~~and ~~Convertible~~Exchange ~~Senior~~Commission ~~Notes~~on ~~due~~April ~~2031~~30, ~~(the “Notes”)~~2026. Based ~~The~~on ~~Notes~~the ~~will~~votes becast ~~issued~~in ~~pursuant~~person toand anby ~~indenture~~proxy, ~~(the~~each ~~“Indenture”)~~proposal passed, ~~between~~including the ~~Company~~election ~~and~~of Ueach director.S. The ~~Bank~~number ~~Trust~~of ~~Company,~~votes ~~National~~cast ~~Association,~~for asand ~~trustee,~~against and the ~~sale~~number of ~~the~~abstentions ~~Notes~~and isbroker ~~expected~~non-votes towith ~~close~~respect ~~on June 10, 2026, subject~~ to ~~customary~~each ~~closing~~matter ~~conditions~~voted ~~(the~~upon ~~“Private~~are ~~Placement”).~~set forth below:

~~When~~Proposal issued pursuant to the Indenture, the Notes will be senior unsecured obligations of the Company and will mature on June 15, 2031, unless earlier converted, redeemed or repurchased. Interest on the Notes will accrue at a rate of 2.25% per year from June 10, 2026 and will be payable semiannually in arrears on June 15 and December 15 of each year, beginning on December 15, 2026. The Notes will be convertible at the option of the noteholders at any time prior to the close of business on the business day immediately preceding March 15, 2031, only upon satisfaction of one or more of the following conditions1: Election ~~(1) during any calendar quarter commencing after the calendar quarter ending on September 30, 2026 (and only during such calendar quarter), if the last reported sale price~~ of the Company’s common stock, par value $0.0001 per share (the “Common Stock”), for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price for the Notes on each applicable trading day; (2) during the five business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the Indenture) per $1,000 principal amount of the Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Common Stock and the conversion rate for the Notes on each such trading day; (3) if the Company calls such Notes for redemption, at any time prior to the close of business on the second scheduled trading day immediately preceding the redemption date, but only with respect to the Notes called (or deemed called) for redemption; or (4) upon the occurrence of specified corporate events as will be set forth in the Indenture. On or after March 15, 2031, until the close of business on the second scheduled trading day immediately preceding the maturity date, noteholders may convert all or any portion of their Notes at their option at any time, regardless of the foregoing conditions. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of Common Stock or a combination of cash and shares of Common Stock, at the Company’s election, in the manner and subject to the terms and conditions that will be provided in the Indenture. directors:

The conversion rate for the Notes will initially be 40.3894 shares of Common Stock per $1,000 principal amount of Notes (equivalent to an initial conversion price of approximately $24.76 per share of Common Stock). The initial conversion price of the Notes represents a premium of approximately 35% over the last reported sale price of the Common Stock on the Nasdaq Global Select Market on June 3, 2026. The conversion rate will be subject to adjustment under certain circumstances in accordance with the terms of the Indenture but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date of the Notes or if the Company delivers a notice of redemption in respect of the Notes, the Company will, in certain circumstances, increase the conversion rate of the Notes for a noteholder who elects to convert its Notes in connection with such a corporate event or notice of redemption, as the case may be.


Nominee	For	Withheld	Broker Non-Votes
Pierre Legault	37,294,888	21,467,975	8,034,588
Michael A. Metzger	58,113,110	649,753	8,034,588

~~The~~Proposal ~~Company~~2: Advisory ~~may~~vote ~~not redeem the Notes prior to June 20, 2029. The Company may redeem for cash all or any portion of the Notes (subject to certain limitations), at the Company’s option,~~ on aexecutive redemption date on or after June 20, 2029 if the last reported sale price of the Common Stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period (including the last trading day of such period) ending on, and including, the trading day immediately preceding the date on which the Company provides notice of redemption at a redemption price equal to 100% of the principal amount of the Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund will be provided for the Notes. compensation:

If the Company undergoes a fundamental change (as defined in the Indenture), then, subject to certain conditions and limited exceptions, noteholders may require the Company to repurchase for cash all or any portion of their Notes at a repurchase price equal to 100% of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.


For	Against	Abstain	Broker Non-Votes
55,688,039	2,985,350	89,474	8,034,588

2Proposal 3: Ratification of selection of independent registered public accounting firm:

The Indenture will include customary covenants and sets forth certain events of default. The following events will be considered “events of default” under the Indenture:


For	Against	Abstain	Broker Non-Votes
66,603,912	162,947	30,592	—

•Proposal ~~default~~4: Approval ~~in any payment~~ of ~~interest on any Note when due and payable, and~~ the ~~default~~2026 ~~continues for a period of 30 days;~~Plan:

• default in the payment of principal of any Note when due and payable at its stated maturity, upon any optional redemption, upon any required repurchase, upon declaration of acceleration or otherwise;


For	Against	Abstain	Broker Non-Votes
33,333,263	25,392,051	37,549	8,034,588

•Proposal ~~failure~~5: Approval byof the ~~Company~~2026 ~~to comply with its obligation to convert the Notes in accordance with the Indenture upon exercise of a noteholder’s conversion right and such failure continues for three business days;~~ESPP:

• failure by the Company to give (i) a fundamental change notice or notice of a make-whole fundamental change (each as described in the Indenture), in either case when due and such failure continues for two business days, or (ii) notice of a specified corporate transaction (as described in the Indenture) when due and such failure continues for one business day;


For	Against	Abstain	Broker Non-Votes
58,661,941	74,047	26,875	8,034,588

Syndax Pharmaceuticals, Inc.

Dated: June 4, 2026

/s/ Michael A. Metzger

Michael A. Metzger

Chief Executive Officer

• failure by the Company to comply with any of the Company’s other agreements in the Notes or the Indenture for 60 days after receipt of written notice of such failure from the trustee or the holders of at least 25% in principal amount of the Notes then outstanding;


Exhibit No.	Description

10.1	Syndax Pharmaceuticals, Inc. 2026 Equity Incentive Plan
10.2	Syndax Pharmaceuticals, Inc. 2026 Employee Stock Purchase Plan
104	Cover Page Interactive Data File (embedded within the Inline XBRL document)

• default by the Company or any of its significant subsidiaries (as defined in the Indenture) with respect to any mortgage, agreement or other instrument under which there may be outstanding, or by which there may be secured or evidenced, any indebtedness for money borrowed with a principal amount in excess of $25,000,000 (or its foreign currency equivalent), in the aggregate of the Company and/or any such significant subsidiary, whether such indebtedness now exists or shall hereafter be created, (i) resulting in such indebtedness becoming or being declared due and payable prior to its stated maturity date or (ii) constituting a failure to pay the principal of any such indebtedness when due and payable (after the expiration of all applicable grace periods) at its stated maturity, upon required repurchase, upon declaration of acceleration or otherwise, and in the cases of clauses (i) and (ii), such acceleration shall not have been rescinded or annulled or such failure to pay or default shall not have been cured or waived, or such indebtedness is not paid or discharged, as the case may be, within 45 days after written notice to the Company by the trustee or to the Company and the trustee by holders of at least 25% in aggregate principal amount of the Notes then outstanding in accordance with the Indenture;SIGNATURES

•Pursuant ato ~~final judgment or judgments for~~ the ~~payment~~requirements of ~~$25,000,000 (or its foreign currency equivalent) or more (excluding any amounts covered by insurance) in~~ the ~~aggregate~~Securities ~~rendered~~Exchange ~~against~~Act ~~the Company or any~~ of ~~its significant subsidiaries~~1934, ~~which judgment is not discharged, bonded, paid, waived or stayed within 60 days after (i)~~ the ~~date~~registrant ~~on which the right to appeal thereof~~ has ~~expired~~duly ifcaused nothis ~~such~~report ~~appeal~~to ~~has~~be ~~commenced,~~signed ~~or (ii) the date~~ on ~~which~~its ~~all~~behalf ~~rights~~by tothe ~~appeal~~undersigned ~~have~~hereunto ~~been~~duly ~~extinguished; and~~authorized.

• certain events of bankruptcy, insolvency or reorganization of the Company or any of the Company’s significant subsidiaries.


			SYNDAX PHARMACEUTICALS, INC.

Date:	June 10, 2026	By:	/s/ Michael A. Metzger
			Michael A. Metzger Chief Executive Officer

If certain bankruptcy and insolvency-related events of default occur with respect to the Company, the principal of, and accrued and unpaid interest, if any, on, all of the then outstanding Notes shall automatically become due and payable. If an event of default, other than certain bankruptcy and insolvency-related events of default with respect to the Company, occurs and is continuing, the trustee, by notice to the Company, or the holders of at least 25% in principal amount of the outstanding Notes by notice to the Company and the trustee, may declare 100% of the principal

of, and accrued interest on all the outstanding Notes to be due and payable. Notwithstanding the foregoing, the Indenture provides that, to the extent the Company so elects, the sole remedy for an event of default relating to certain failures by the Company to comply with certain reporting covenants in the Indenture will, for the first 365 days after the occurrence of such an event of default, consist exclusively of the right to receive additional interest on the Notes.

The Indenture provides that the Company shall not consolidate with or merge with or into, or sell, convey, transfer or lease all or substantially all of the consolidated properties and assets of the Company and its subsidiaries, taken as a whole, to, another person (other than any such sale, conveyance, transfer or lease to one or more of the Company’s direct or indirect wholly owned subsidiaries), unless: (i) the resulting, surviving or transferee person (if not the Company) is a qualified successor entity (as defined in the Indenture) (such qualified successor entity, the “successor entity”) organized and existing under the laws of the United States of America, any state thereof or the District of Columbia, and such successor entity (if not the Company) expressly assumes by supplemental indenture all of the Company’s obligations under the Notes and the Indenture; and (ii) immediately after giving effect to such transaction, no default or event of default has occurred and is continuing under the Indenture.

A copy of the form of Subscription Agreement is attached as Exhibit 10.1 to this Current Report on Form 8-K and is incorporated herein by reference (and the foregoing description is qualified in its entirety by reference to such document).

Proceeds

The Company estimates that the net proceeds from the Private Placement will be approximately $243 million, after deducting the placement agent’s fees and Private Placement expenses payable by the Company. The Company expects to use the net proceeds from the Private Placement for general corporate purposes, including working capital, research and development expenditures, commercialization activity expenditures and business development expenditures.

Item 2.03 Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant.

The information set forth under Item 1.01 of this Current Report on Form 8-K is incorporated herein by reference.

Item 3.02 Unregistered Sale of Equity Securities.

The information set forth under Item 1.01 of this Current Report on Form 8-K is incorporated herein by reference.

The Company offered and sold the Notes to certain investors in reliance on the exemption from registration provided by Section 4(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”). The Company relied on this exemption from registration based in part on representations made by each investor in the Subscription Agreements.

The Notes and the shares of Common Stock issuable upon conversion of the Notes, if any, have not been registered under the Securities Act and may not be offered or sold in the United States absent registration or an applicable exemption from registration requirements.

To the extent that any shares of Common Stock are issued upon conversion of the Notes, they will be issued in transactions anticipated to be exempt from registration under the Securities Act by virtue of Section 3(a)(9) thereof as involving an exchange by the Company exclusively with its noteholders because no commission or other remuneration is expected to be paid in connection with conversion of the Notes and any resulting issuance of shares of Common Stock. Initially, a maximum of 13,631,400 shares of Common Stock may be issued upon conversion of the Notes based on the initial maximum conversion rate of 54.5256 shares of Common Stock per $1,000 principal amount of Notes, which is subject to customary anti-dilution adjustment provisions.

Item 8.01 Other Events.

On June 4, 2026, the Company issued a press release announcing the pricing of the Notes. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

Forward-Looking Statements

This Current Report on Form 8-K contains “forward-looking statements” within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended, including statements regarding, among other things, the terms of the Notes and the Company’s anticipated use of the net proceeds from the Offering. These forward-looking statements are based on the Company’s current assumptions, expectations and beliefs and are subject to substantial risks, uncertainties, assumptions and changes in circumstances that may cause the Company’s actual results, performance or achievements to differ materially from those expressed or implied in any forward-looking statement. These risks include, but are not limited to market risks, trends and conditions. Other factors that may cause the Company’s actual results to differ from those expressed or implied in the forward-looking statements in this Current Report on Form 8-K are discussed in the Company’s filings with the U.S. Securities and Exchange Commission, including the “Risk Factors” sections contained therein. Except as required by law, the Company assumes no obligation to update any forward-looking statements contained herein to reflect any change in expectations, even as new information becomes available.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits

ExhibitNo.		Description
10.1		Form of Subscription Agreement
99.1		Press release entitled “Syndax Announces Private Placement of $250.0 Million of Convertible Senior Notes,” dated June 4, 2026
104		Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

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

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