Form 8-K

8-K — APPLIED OPTOELECTRONICS, INC.

Accession: 0001683168-26-003572

Filed: 2026-05-08

Period: 2026-05-04

CIK: 0001158114

SIC: 3674 (SEMICONDUCTORS & RELATED DEVICES)

Item: Changes in Registrant's Certifying Accountant

Item: Financial Statements and Exhibits

Documents

8-K — aaoi_8k.htm (Primary)

EX-16.1 — LETTER FROM GRANT THORNTON LLP (aaoi_1601.htm)

XML — IDEA: XBRL DOCUMENT (R1.htm)

8-K — FORM 8-K

8-K (Primary)

Filename: aaoi_8k.htm · Sequence: 1

Applied Optoelectronics, Inc. 10-Q

false

0001158114

2026-05-04

iso4217:USD

xbrli:shares

iso4217:USD

xbrli:shares

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 4, 2026

Applied Optoelectronics, Inc.

(Exact name of registrant as specified

in its charter)

Delaware

001-36083

76-0533927

(State of incorporation)

(Commission File Number)

(I.R.S. Employer Identification No.)

13139

Jess Pirtle Blvd.

Sugar

Land, Texas 77478

(Address

of principal executive offices and zip code)

(281) 295-1800

(Registrant’s telephone number, including

area code)

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

(see General Instruction A.2. below):

¨ 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 Act:

Title

of each class

Trading

Symbol(s)

Trading

Name of each exchange on which registered

Common

Stock, Par value $0.001

AAOI

NASDAQ

Global Market

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

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. o

Item 4.01. Changes in Registrant’s Certifying Accountant.

(a) Dismissal of Independent Registered Public Accounting Firm

The Audit Committee (the “Committee”)

of the Board of Directors of Applied Optoelectronics, Inc. (the “Company”) recently completed a competitive selection process,

inclusive of the Company’s current independent registered public accounting firm, Grant Thornton LLP (“Grant Thornton”),

to determine the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2026. Following

the review and evaluation of the proposals of the participating firms, on May 4, 2026, the Committee approved the dismissal of Grant Thornton

as the Company’s independent registered public accounting firm. Grant Thronton was previously engaged to perform a review of the

Company’s consolidated financial statements for the quarter ending March 31, 2026. The dismissal of Grant Thornton does not affect

its engagement for the quarter ending March 31, 2026.

Grant Thornton’s reports on the Company’s

consolidated financial statements as of and for the fiscal years ended December 31, 2025 and 2024 did not contain any adverse opinion

or disclaimer of opinion, nor were they qualified or modified as to uncertainty, audit scope, or accounting principles. During the fiscal

years ended December 31, 2025 and 2024 and the subsequent interim period through May 4, 2026, there were no disagreements (as defined

in Item 304(a)(1)(iv) of Regulation S-K and the related instructions) with Grant Thornton on any matter of accounting principles or practices,

financial statement disclosure, or auditing scope or procedures, which disagreements, if not resolved to Grant Thornton’s satisfaction,

would have caused Grant Thornton to make reference thereto in their reports.

There were no “reportable events” (as

that term is defined in Item 304(a)(1)(v) of Regulation S-K) during either of the years ended December 31, 2024 and 2025, and the subsequent

interim period through May 4, 2026, except for the material weakness in the Company’s operation of controls over its review of technical

accounting analysis, as first disclosed in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2024,

which material weakness was remediated as of December 31, 2025.

The Company provided Grant Thornton with a copy

of this Current Report on Form 8-K prior to its filing with the United States Securities and Exchange Commission (the “SEC”)

and requested that Grant Thornton furnish a letter addressed to the SEC stating whether or not it agrees with the statements made herein,

as specified by Item 304(a)(3) of Regulation S-K. A copy of Grant Thornton’s letter, dated May 8, 2026, is filed as Exhibit 16.1

to this Current Report on Form 8-K.

(b) Appointment of New Independent Registered Public Accounting Firm

As a result of the process noted above and following

the review and evaluation of proposals from all participating firms, on May 4, 2026, the Committee approved the appointment of PricewaterhouseCoopers

LLP (“PwC”) as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2026.

During the fiscal years ended December 31, 2025

and 2024 and the subsequent interim period through May 4, 2026, neither the Company nor anyone on its behalf consulted with PwC regarding

the application of accounting principles to a specified transaction, either completed or proposed, the type of audit opinion that would

have been rendered on the Company’s consolidated financial statements, or any matter that was the subject of a “disagreement”

(as that term is defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions) or any “reportable event” (as

that term is defined in Item 304(a)(1)(v) of Regulation S-K) or any other matters set forth in Item 304(a)(2)(i) or (ii) of Regulation

S-K.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits.

Exhibit No.

Description

16.1

Grant Thornton’s letter

104

Cover Page Interactive File (the cover page tags are embedded within the Inline XBRL document).

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.

APPLIED OPTOELECTRONICS, INC.

By:

/s/ Stefan J. Murry

Stefan J. Murry

Chief Financial Officer

Date: May 8, 2026

EX-16.1 — LETTER FROM GRANT THORNTON LLP

EX-16.1

Filename: aaoi_1601.htm · Sequence: 2

Exhibit 16.1

May 8, 2026

U.S. Securities and Exchange Commission

Office of the Chief Accountant

100 F Street, NE

Washington, DC 20549

Re:

Applied Optoelectronics, Inc.

File No. 001-36083

Dear Sir or Madam:

We have read Item 4.01 of Form 8-K of Applied Optoelectronics, Inc.

May 8, 2026, and agree with the statements concerning our Firm contained therein.

Very truly yours,

/s/ GRANT THORNTON LLP

XML — IDEA: XBRL DOCUMENT

XML

Filename: R1.htm · Sequence: 7

v3.26.1

Cover

May 04, 2026

Cover [Abstract]

Document Type

8-K

Amendment Flag

false

Document Period End Date

May 04, 2026

Entity File Number

001-36083

Entity Registrant Name

Applied Optoelectronics, Inc.

Entity Central Index Key

0001158114

Entity Tax Identification Number

76-0533927

Entity Incorporation, State or Country Code

Entity Address, Address Line One

13139

Jess Pirtle Blvd.

Entity Address, City or Town

Sugar

Land

Entity Address, State or Province

Entity Address, Postal Zip Code

77478

City Area Code

281

Local Phone Number

295-1800

Written Communications

false

Soliciting Material

false

Pre-commencement Tender Offer

false

Pre-commencement Issuer Tender Offer

false

Title of 12(b) Security

Common

Stock, Par value $0.001

Trading Symbol

AAOI

Security Exchange Name

NASDAQ

Entity Emerging Growth Company

false

- 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

Cover page.

+ References

No definition available.

+ Details

Name:

dei_CoverAbstract

Namespace Prefix:

dei_

Data Type:

xbrli:stringItemType

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

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

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