Form 8-K

8-K — Sensei Biotherapeutics, Inc.

Accession: 0001193125-26-234882

Filed: 2026-05-21

Period: 2026-05-21

CIK: 0001829802

SIC: 2834 (PHARMACEUTICAL PREPARATIONS)

Item: Other Events

Item: Financial Statements and Exhibits

Documents

8-K — d162035d8k.htm (Primary)

EX-99.1 (d162035dex991.htm)

XML — IDEA: XBRL DOCUMENT (R1.htm)

8-K

8-K (Primary)

Filename: d162035d8k.htm · Sequence: 1

8-K

false 0001829802 0001829802 2026-05-21 2026-05-21 0001829802 dei:FormerAddressMember 2026-05-21 2026-05-21

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 21, 2026

Sensei Biotherapeutics, Inc.

(Exact Name of Registrant as Specified in its Charter)

Delaware

001-39980

83-1863385

(State or Other Jurisdiction

of Incorporation)

(Commission

File Number)

(IRS Employer

Identification No.)

1405 Research Blvd, Suite 125

Rockville, MD

20850

(Address of Principal Executive Offices)

(Zip Code)

451 D Street, Suite 710

Boston, MA

02210

(Former Address of Principal Executive Offices)

(Zip Code)

Registrant’s telephone number, including area code: (240) 243-8000

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:

☐

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

☐

Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐

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

☐

Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Securities Exchange Act of 1934:

Title of each class

Trading

symbol

Name of each exchange

on which registered

Common Stock

SNSE

The Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☒

If an 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 Section 13(a) of the Exchange Act. ☐

Item 8.01.

Other Events.

As previously announced, Sensei Biotherapeutics, Inc. (the “Company”) will hold its 2026 annual meeting of stockholders (“Annual Meeting”) of the Company on June 10, 2026, at 11:00 a.m. Eastern Daylight Time, unless postponed or adjourned to a later date. At the Annual Meeting, stockholders will be asked to approve, among other things, the issuance of shares of common stock, par value $0.0001 per share (“common stock”), of the Company upon conversion of Series B Non-Voting Convertible Preferred Stock, par value $0.0001 per shares (“Series B Preferred Stock”), which will (a) represent more than 20% of the shares of common stock outstanding and (b) result in the change of control of the Company pursuant to Nasdaq Listing Rules 5635(a) and 5635(b), respectively. In connection with the Annual Meeting, the Company is filing unaudited pro forma condensed consolidated financial information of the Company for the quarter ended March 31, 2026, presenting the historical consolidated financial position of the Company for the quarter ended March 31, 2026, adjusted to give effect to the conversion of the shares of Series B Preferred Stock into shares of common stock.

The unaudited pro forma condensed financial information, including the notes thereto, should be read in conjunction with the financial statements of the Company and the Company’s management’s discussion and analysis of financial condition and results of operations included in the Company’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2026, filed with the Securities and Exchange Commission (“SEC”) on May 15, 2026. Such unaudited pro forma condensed financial information is presented for illustrative purposes only and may not be an indication of the Company’s financial condition following the conversion of the Series B Preferred Stock for several reasons. The unaudited pro forma condensed financial information has been derived from the historical unaudited financial statements of the Company for the quarter ended March 31, 2026, and certain adjustments and assumptions have been made regarding the Company after giving effect to the conversion of the Series B Preferred Stock. The information upon which these adjustments and assumptions have been made is preliminary, and these kinds of adjustments and assumptions are difficult to make with accuracy. Moreover, the unaudited pro forma condensed financial information does not reflect all costs that are expected to be incurred by the Company in connection with the conversion of the Series B Preferred Stock. As a result, the actual financial condition of the Company following the conversion of the Series B Preferred Stock may not be consistent with, or evident from, the unaudited pro forma condensed financial information. The assumptions used in preparing the unaudited pro forma condensed financial information may not prove to be accurate, and other factors may affect the Company’s financial condition following the conversion of the Series B Preferred Stock. For more information, please see Exhibit 99.1 attached hereto and incorporated herein by reference.

For more information regarding the Annual Meeting, please refer to the Company’s Definitive Proxy Statement, filed with the SEC on April 27, 2026.

Item 9.01

Financial Statements and Exhibits.

(d) Exhibits

Exhibit

Number

Exhibit Description

99.1

Unaudited Pro Forma Condensed Financial Information of Sensei Biotherapeutics, Inc. for the quarter ended March 31, 2026.

104

The cover page from this Current Report on Form 8-K, formatted in Inline XBRL

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 hereunto duly authorized.

Sensei Biotherapeutics, Inc.

Date: May 21, 2026

/s/ Christopher W. Gerry

Christopher W. Gerry

President and General Counsel

EX-99.1

Filename: d162035dex991.htm · Sequence: 2

EX-99.1

Exhibit 99.1

SENSEI BIOTHERAPEUTICS, INC.

UNAUDITED PRO FORMA CONDENSED FINANCIAL INFORMATION

On February 17, 2026, Sensei Biotherapeutics, Inc. (the “Company”) acquired Faeth Holdings Therapeutics, Inc. (“Faeth HoldCo”)

and its wholly owned subsidiary Faeth Therapeutics, LLC (“Faeth Subsidiary” and, together with Faeth HoldCo, “Faeth Therapeutics” or “Faeth”) pursuant to an Agreement and Plan of Merger (the “Merger

Agreement”), dated as of February 17, 2026, by and among the Company, its merger subsidiaries, Faeth HoldCo and Faeth Subsidiary (such transaction, the “Acquisition”).

Under the terms of the Merger Agreement, the Company issued to the stockholders of Faeth an aggregate of 10,497.0980 shares of Series B Non-Voting Convertible Preferred Stock, par value $0.0001 per share (the “Series B Preferred Stock”), representing 10,497,098 shares of common stock of the Company, par value $0.0001 per

share (“Common Stock”), on an as-converted-to-common basis and without giving effect to any beneficial ownership

limitations.

Concurrently with the acquisition of Faeth Therapeutics, on February 17, 2026, the Company entered into a Securities Purchase Agreement

(the “Purchase Agreement”) with new and returning investors to raise $200.0 million of gross proceeds in which investors were issued an aggregate of 14,440.395 shares of Series B Preferred Stock, or 14,440,395 on an as-converted-to-common basis and without giving effect to any beneficial ownership limitations, (the “PIPE Securities”) at

a price of $13,850 per share, or $13.85 per share on an as-converted-to-common basis, (collectively, the

“Financing”). The Financing closed on February 20, 2026.

Subject to the receipt of stockholder approval of the Parent Stockholder

Matters (as defined in the Merger Agreement), each share of Series B Preferred Stock will automatically convert into 1,000 shares of Common Stock, subject to certain beneficial ownership limitations established by each holder.

The following unaudited pro forma condensed financial information presents the historical consolidated financial position and results of operations of

the Company, adjusted to give effect to the conversion of the Series B Preferred Stock into common stock (the “Conversion”) that will automatically occur three business days subsequent to the expected affirmative vote for stockholder

approval of the Parent Stockholder Matters. The vote for stockholder approval of the Parent Stockholder Matters is scheduled to occur on June 10, 2026. The unaudited pro forma condensed balance sheet gives pro forma effect to the Conversion as

if it had been consummated on March 31, 2026. The unaudited pro forma condensed statement of operations for the three months ended March 31, 2026 gives effect to the Conversion as if it had occurred on January 1, 2026.

The unaudited pro forma condensed financial information is based on the assumptions and adjustments described in the accompanying notes. Accordingly, the

pro forma adjustments are preliminary, subject to further revision as additional information becomes available and additional analyses are performed and have been made solely for the purpose of providing unaudited pro forma condensed

financial information.

The unaudited pro forma condensed financial information, including the notes thereto, should be read in conjunction with the

financial statements of the Company and the Company’s management’s discussion and analysis of financial condition and results of operations included in the Company’s Quarterly Report on Form

10-Q for the quarter ended March 31, 2026, filed with the Securities and Exchange Commission (“SEC”) on May 15, 2026.

UNAUDITED PRO FORMA CONDENSED BALANCE SHEET

AS OF MARCH 31, 2026

(in thousands)

Transaction Accounting Adjustments

March 31,

2026

Conversion

Note

References

Pro Forma As

Adjusted

Assets

Current assets:

Cash and cash equivalents

152,325

—

152,325

Marketable securities

50,468

Prepaid expenses

974

Other current assets

465

Total current assets

204,232

—

204,232

Right-of-use

assets - operating leases, net

913

Right-of-use

assets - financing leases, net

—

Property and equipment, net

Other non-current assets

167

Total assets

205,381

—

205,381

Liabilities, redeemable convertible preferred stock and stockholders’ (deficit)

equity

Current liabilities:

Accounts payable and accrued expenses

8,982

—

8,982

Compensation and employee benefits liabilities

4,169

Operating lease liabilities, current

1,021

Financing lease liabilities, current

Total current liabilities

14,190

—

14,190

Operating lease liabilities, non-current

—

Other non-current liabilities

—

Total liabilities

14,191

—

14,191

Commitments and contingencies

Series B redeemable convertible preferred stock

328,476

(321,856

)

6,620

Stockholders’ (deficit) equity:

Common stock

—

Additional paid-in capital

316,111

321,854

637,965

Accumulated deficit

(453,373

)

(453,373

)

Accumulated other comprehensive (loss) income

(24

)

(24

)

Total stockholders’ (deficit) equity

(137,286

)

321,856

184,570

Total liabilities, redeemable convertible preferred stock, and stockholders’ (deficit)

equity

205,381

—

205,381

UNAUDITED PRO FORMA CONDENSED STATEMENT OF OPERATIONS

FOR THE THREE MONTHS ENDED MARCH 31, 2026

(in thousands, except share and per share amounts)

For the Three Months Ended March 31, 2026

Transaction

Accounting

Adjustments

Actual

Conversion

Note

References

Pro Forma As

Adjusted

Operating expenses:

Research and development

17,957

—

17,957

General and administrative

19,713

Acquired in-process research and development

132,957

Total operating expenses

170,627

Loss from operations

(170,627)

Other income (expense), net:

Interest income, net

392

Other (expense) income, net

(1)

Net loss

(170,236)

—

(170,236)

Net loss per common share, basic and diluted

(131.45)

(6.62)

Weighted-average shares outstanding, basic and diluted

1,295,052

24,434,920

25,729,972

Comprehensive loss:

Net loss

(170,236)

—

(170,236)

Other comprehensive items:

Unrealized (loss) gain on marketable securities

(25)

Total other comprehensive (loss) income

(25

)

(25

)

Total comprehensive loss

(170,261)

—

(170,261)

SENSEI BIOTHERAPEUTICS, INC.

NOTES TO UNAUDITED PRO FORMA CONDENSED BALANCE SHEET

Note 1. Transaction accounting adjustments for the Conversion

Reflects the expected conversion of 24,434.92 shares of Series B Preferred Stock into 24,434,920 shares

of common stock that will automatically occur three business days subsequent to the expected affirmative vote for the Conversion. The aforementioned vote is scheduled to occur on June 10, 2026. The transaction accounting adjustments reflecting

the Conversion do not reflect the conversion of shares of Series B Preferred Stock that are not expected to convert due to certain beneficial ownership limitations established by each holder based solely on the shares of Series B Preferred Stock

beneficially owned by the holders thereof. The number of shares of Series B Preferred Stock that ultimately convert into shares of common stock may be more or less than our expectations.

XML — IDEA: XBRL DOCUMENT

XML

Filename: R1.htm · Sequence: 8

v3.26.1

Document and Entity Information

May 21, 2026

Document And Entity Information [Line Items]

Document Type

8-K

Document Period End Date

May 21, 2026

Entity Registrant Name

Sensei Biotherapeutics, Inc.

Entity Incorporation State Country Code

Entity File Number

001-39980

Entity Tax Identification Number

83-1863385

Entity Address Address Line 1

1405 Research Blvd

Entity Address Address Line 2

Suite 125

Entity Address City Or Town

Rockville

Entity Address State Or Province

Entity Address Postal Zip Code

20850

City Area Code

240

Local Phone Number

243-8000

Written Communications

false

Soliciting Material

false

Pre Commencement Tender Offer

false

Pre Commencement Issuer Tender Offer

false

Security 12b Title

Common Stock

Trading Symbol

SNSE

Security Exchange Name

NASDAQ

Entity Emerging Growth Company

true

Entity Ex Transition Period

false

Amendment Flag

false

Entity Central Index Key

0001829802

Former Address [Member]

Document And Entity Information [Line Items]

Entity Address Address Line 1

451 D Street

Entity Address Address Line 2

Suite 710

Entity Address City Or Town

Boston

Entity Address State Or Province

Entity Address Postal Zip Code

02210

- Definition

Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.

+ References

No definition available.

+ Details

Name:

dei_AmendmentFlag

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Area code of city

+ References

No definition available.

+ Details

Name:

dei_CityAreaCode

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD.

+ References

No definition available.

+ Details

Name:

dei_DocumentPeriodEndDate

Namespace Prefix:

dei_

Data Type:

xbrli:dateItemType

Balance Type:

Period Type:

duration

- Definition

The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.

+ References

No definition available.

+ Details

Name:

dei_DocumentType

Namespace Prefix:

dei_

Data Type:

dei:submissionTypeItemType

Balance Type:

Period Type:

duration

- Definition

Address Line 1 such as Attn, Building Name, Street Name

+ References

No definition available.

+ Details

Name:

dei_EntityAddressAddressLine1

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Address Line 2 such as Street or Suite number

+ References

No definition available.

+ Details

Name:

dei_EntityAddressAddressLine2

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Name of the City or Town

+ References

No definition available.

+ Details

Name:

dei_EntityAddressCityOrTown

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Code for the postal or zip code

+ References

No definition available.

+ Details

Name:

dei_EntityAddressPostalZipCode

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Name of the state or province.

+ References

No definition available.

+ Details

Name:

dei_EntityAddressStateOrProvince

Namespace Prefix:

dei_

Data Type:

dei:stateOrProvinceItemType

Balance Type:

Period Type:

duration

- Definition

A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityCentralIndexKey

Namespace Prefix:

dei_

Data Type:

dei:centralIndexKeyItemType

Balance Type:

Period Type:

duration

- Definition

Indicate if registrant meets the emerging growth company criteria.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityEmergingGrowthCompany

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Indicate if an emerging growth company has elected not to use the extended transition period for complying with any new or revised financial accounting standards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Securities Act

-Number 7A

-Section B

-Subsection 2

+ Details

Name:

dei_EntityExTransitionPeriod

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen.

+ References

No definition available.

+ Details

Name:

dei_EntityFileNumber

Namespace Prefix:

dei_

Data Type:

dei:fileNumberItemType

Balance Type:

Period Type:

duration

- Definition

Two-character EDGAR code representing the state or country of incorporation.

+ References

No definition available.

+ Details

Name:

dei_EntityIncorporationStateCountryCode

Namespace Prefix:

dei_

Data Type:

dei:edgarStateCountryItemType

Balance Type:

Period Type:

duration

- Definition

The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityRegistrantName

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b-2

+ Details

Name:

dei_EntityTaxIdentificationNumber

Namespace Prefix:

dei_

Data Type:

dei:employerIdItemType

Balance Type:

Period Type:

duration

- Definition

Local phone number for entity.

+ References

No definition available.

+ Details

Name:

dei_LocalPhoneNumber

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 13e

-Subsection 4c

+ Details

Name:

dei_PreCommencementIssuerTenderOffer

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 14d

-Subsection 2b

+ Details

Name:

dei_PreCommencementTenderOffer

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Title of a 12(b) registered security.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection b

+ Details

Name:

dei_Security12bTitle

Namespace Prefix:

dei_

Data Type:

dei:securityTitleItemType

Balance Type:

Period Type:

duration

- Definition

Name of the Exchange on which a security is registered.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 12

-Subsection d1-1

+ Details

Name:

dei_SecurityExchangeName

Namespace Prefix:

dei_

Data Type:

dei:edgarExchangeCodeItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as soliciting material pursuant to Rule 14a-12 under the Exchange Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Exchange Act

-Number 240

-Section 14a

-Subsection 12

+ Details

Name:

dei_SolicitingMaterial

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- Definition

Trading symbol of an instrument as listed on an exchange.

+ References

No definition available.

+ Details

Name:

dei_TradingSymbol

Namespace Prefix:

dei_

Data Type:

dei:tradingSymbolItemType

Balance Type:

Period Type:

duration

- Definition

Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as written communications pursuant to Rule 425 under the Securities Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Securities Act

-Number 230

-Section 425

+ Details

Name:

dei_WrittenCommunications

Namespace Prefix:

dei_

Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

duration

- References

No definition available.

+ Details

Name:

snse_DocumentAndEntityInformationLineItems

Namespace Prefix:

snse_

Data Type:

xbrli:stringItemType

Balance Type:

Period Type:

duration

- Details

Name:

dei_EntityAddressesAddressTypeAxis=dei_FormerAddressMember

Namespace Prefix:

Data Type:

Balance Type:

Period Type: