Form 8-K

8-K — BYLINE BANCORP, INC.

Accession: 0001193125-26-415585

Filed: 2026-10-06

Period: 2026-10-06

CIK: 0001702750

SIC: 6022 (STATE COMMERCIAL BANKS)

Item: Regulation FD Disclosure

Item: Financial Statements and Exhibits

Documents

8-K — by-20261006.htm (Primary)

EX-99.1 (by-ex99_1.htm)

EX-99.2 (by-ex99_2.htm)

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8-K

8-K (Primary)

Filename: by-20261006.htm · Sequence: 1

8-K

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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): October 06, 2026

BYLINE BANCORP, INC.

(Exact Name of Registrant as Specified in Its Charter)

Delaware

001-38139

36-3012593

(State or Other Jurisdiction

of Incorporation)

(Commission File Number)

(IRS Employer

Identification No.)

180 North LaSalle Street, Suite 300

Chicago, Illinois

60601

(Address of Principal Executive Offices)

(Zip Code)

(773) 244-7000

(Registrant’s Telephone Number, Including Area Code)

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

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 Act:

Title of each class

Trading

Symbol(s)

Name of each exchange on which registered

Common Stock

The New York Stock Exchange

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 7.01 Regulation FD Disclosure.

On October 6, 2026, Byline Bancorp, Inc., a Delaware corporation ("Byline"), issued a press release announcing the execution of an Agreement and Plan of Merger in connection with its proposed acquisition of Illinois State Bancorp, Inc., an Illinois corporation ("Illinois State Bancorp"), and Illinois State Bancorp's wholly owned bank subsidiaries, First Nations Bank, an Illinois chartered bank, and The Bank of Bourbonnais, an Illinois chartered bank. Byline has also provided supplemental information regarding the proposed transaction. A copy of the press release is attached to this report as Exhibit 99.1 and a copy of the supplemental materials is attached as Exhibit 99.2, both of which are incorporated herein by reference.

The information furnished pursuant to Item 7.01 of this Current Report on Form 8-K (including Exhibit 99.1 and Exhibit 99.2 hereto) is being furnished and shall not be deemed “filed” under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), nor shall it be incorporated by reference into future filings by Byline under the Securities Act of 1933, as amended (the “Securities Act”), or under the Exchange Act, except as expressly set forth by specific reference in such a filing. The furnishing of information pursuant to this Item 7.01 will not be deemed an admission as to the materiality of any information in this Current Report on Form 8-K that is required to be disclosed solely by Regulation FD.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

Exhibit

No.

Description

99.1

Press Release dated October 6, 2026

99.2

Investor Presentation dated October 6, 2026

104

Cover Page Interactive Data File (embedded within the Inline XBRL document)

Important Additional Information and Where to Find It

This communication is being made in respect of the proposed merger transaction involving Byline and Illinois State Bancorp. Byline intends to file a registration statement on Form S-4 with the Securities and Exchange Commission (the “SEC”), which will include a proxy statement of Illinois State Bancorp and a prospectus of Byline, and Byline will file other documents regarding the proposed transaction with the SEC. A definitive proxy statement/prospectus will also be sent to Illinois State Bancorp shareholders seeking approval of the proposed transaction. Before making any voting or investment decision, investors and security holders of Illinois State Bancorp are urged to carefully read the entire registration statement and proxy statement/prospectus, when they become available, as well as any amendments or supplements to these documents, because they will contain important information about the proposed transaction. The documents filed by Byline with the SEC may be obtained free of charge at the SEC’s website at www.sec.gov. In addition, the documents filed by Byline may be obtained free of charge at its website at http://www.bylinebancorp.com/Docs. Alternatively, these documents, when available, can be obtained free of charge from Byline upon written request to Byline Bancorp, Inc., Attn: Brian F. Doran, General Counsel & Corporate Secretary, 180 North LaSalle Street, 3rd Floor, Chicago, Illinois 60601, or by calling (773) 244-7000.

Information regarding the interests of certain of Illinois State Bancorp’s directors and executive officers and a description of their direct and indirect interests, by security holdings or otherwise, will be included in the registration statement on Form S-4 regarding the proposed transaction when it becomes available.

Forward-Looking Statements

This communication may contain “forward-looking statements” within the meaning of the U.S. federal securities laws. Forward-looking statements include, without limitation, statements concerning plans, estimates, calculations, forecasts and projections with respect to the anticipated future performance of the Company. These statements are often, but not always, made through the use of words or phrases such as ‘‘may’’, ‘‘might’’, ‘‘should’’, ‘‘could’’, ‘‘predict’’, ‘‘potential’’, ‘‘believe’’, ‘‘expect’’, ‘‘continue’’, ‘‘will’’, ‘‘anticipate’’, ‘‘seek’’, ‘‘estimate’’, ‘‘intend’’, ‘‘plan’’, ‘‘projection’’, ‘‘would’’, ‘‘annualized’’, “target” and ‘‘outlook’’, or the negative version of those words or other comparable words or phrases of a future or forward-looking nature. Accordingly, these statements involve estimates and known and unknown risks, and reflect various assumptions and involve elements of judgment and analysis, which may or may not prove to be correct, and which are subject to uncertainties and contingencies outside the control of Byline which could cause actual results to differ materially from those expressed in this communication. No representations, warranties or guarantees are or will be made by Byline as to the reliability, accuracy or completeness of any forward-looking statements contained in this communication or that such forward-looking statements are or

will remain based on reasonable assumptions. You should not place undue reliance on any forward-looking statements contained in this communication.

Factors that may cause such actual results to differ from those expressed in such forward-looking statements include, but are not limited to, the reaction to the transaction of the companies’ customers, employees and counterparties; customer disintermediation; expected synergies, cost savings and other financial benefits of the proposed transaction might not be realized within the expected timeframes or might be less than projected; the requisite shareholder and regulatory approvals for the proposed transaction might not be obtained; credit and interest rate risks associated with Byline’s and Illinois State Bancorp’s respective businesses, customers, borrowings, repayment, investment, and deposit practices; inflation; general economic conditions, either nationally or in the market areas in which Byline and Illinois State Bancorp operate or anticipate doing business, are less favorable than expected; new regulatory or legal requirements or obligations; and other risks. Certain risks and important factors that could affect Byline’s future results are identified in its Annual Report on Form 10-K for the year ended December 31, 2025 and other reports filed with the SEC, including among other things under the heading “Risk Factors” in such Annual Report on Form 10-K. Any forward-looking statement speaks only as of the date on which it is made, and Byline undertakes no obligation to update any forward-looking statement, whether to reflect events or circumstances after the date on which the statement is made, to reflect new information or the occurrence of unanticipated events, or otherwise unless required under the federal securities laws.

Participants in this Transaction

Byline, Illinois State Bancorp, their respective directors and executive officers and certain of their other members of management and employees may be deemed to be participants in the solicitation of proxies from Illinois State Bancorp shareholders in connection with the proposed transaction. Information about the directors and executive officers of Byline may be found in Byline’s Annual Report on Form 10-K for the year ended December 31, 2025, as filed with the SEC on February 27, 2026 and in Byline’s proxy statement for its 2026 Annual Meeting of Stockholders, as filed with the SEC on April 20, 2026, copies of which can be obtained free of charge from Byline or from the SEC’s website as indicated above. To the extent the holdings of Byline’s securities by its directors and executive officers have changed since the amounts set forth in Byline’s proxy statement for its 2026 Annual Meeting of Stockholders, such changes have been or will be reflected on Statement of Changes in Beneficial Ownership on Form 4 filed with the SEC. In addition, information about the directors and executive officers of Byline and Illinois State Bancorp and other persons who may be deemed participants in the transaction will be included in the proxy statement/prospectus and other relevant materials when filed with the SEC.

SIGNATURE

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.

BYLINE BANCORP, INC.

Date:

October 6, 2026

By:

/s/ Roberto R. Herencia

Name: Roberto R. Herencia

Title: Executive Chairman and Chief Executive Officer

EX-99.1

Filename: by-ex99_1.htm · Sequence: 2

EX-99.1

Exhibit 99.1

Byline Bancorp, Inc. and ILLINOIS STATE Bancorp, Inc. Announce Definitive Merger Agreement

Chicago, IL, October 6, 2026 – Byline Bancorp, Inc. (“Byline”) (NYSE: BY), and Illinois State Bancorp, Inc. ("Illinois State Bancorp"), today jointly announced that they have entered into a definitive merger agreement pursuant to which Illinois State Bancorp and its wholly owned banking subsidiaries will merge with and into Byline Bancorp, Inc. in a cash and stock transaction valued at approximately $87.9 million, based upon Byline's closing stock price on October 5, 2026.

The transaction enhances Byline's presence throughout the Chicago market by adding a stable core deposit base, expanding customer relationships, and increasing market density across key communities. Upon closing, the combined franchise will operate 48 branches with approximately $10.5 billion in assets, $8.0 billion in loans, and $8.4 billion in deposits.

Illinois State Bancorp, Inc., headquartered in Chicago, Illinois, is the parent company of First Nations Bank and The Bank of Bourbonnais. As of June 30, 2026, on a consolidated basis, Illinois State Bancorp had total assets of approximately $617.3 million, total loans of $470.5 million, and total deposits of $510.5 million. For more than 35 years, Illinois State Bancorp has been committed to providing relationship-driven commercial and community banking services across the Chicagoland and Kankakee County markets. Through its banking subsidiaries, Illinois State Bancorp serves customers from three branch locations in Chicagoland and one branch location in Bourbonnais, Illinois.

Roberto R. Herencia, Executive Chairman and Chief Executive Officer of Byline Bancorp, Inc., stated, “This partnership represents another meaningful step in Byline's growth strategy and further strengthens our position in the Chicago market. Illinois State Bancorp has developed deep customer relationships and a strong community banking franchise. Together, we will be well-positioned to continue delivering the local decision-making, personalized service, and financial expertise our customers value while advancing our goal of becoming the preeminent commercial bank in Chicago.”

“At Byline, we have always believed that successful partnerships begin with shared values, strong cultures, and a common commitment to serving customers and communities. Illinois State Bancorp embodies those qualities and has established an outstanding reputation across the markets it serves,” said Alberto J. Paracchini, President of Byline Bancorp, Inc. “We are pleased to add this high-quality and complementary Chicago-area franchise, which enhances our presence in attractive markets, expands our customer reach, and adds a stable core deposit base. We believe this partnership will drive sustainable growth, enhance long-term stockholder value, and reinforce our commitment to the local markets and communities we proudly serve.”

Florian J. Barbi, Chairman, President and Chief Executive Officer of Illinois State Bancorp, Inc., said, “When evaluating the future of our franchise, it was critical to identify a partner that would preserve the values and customer-focused culture that define Illinois State Bancorp. We found that partner in Byline, whose strong Chicago market presence, relationship-driven approach to banking, commitment to local decision-making, and continued investment in technology, innovation, and fraud management closely align with our vision for the future. We believe this partnership will create meaningful opportunities for our customers, employees, and communities while building on the strengths of both organizations.”

Transaction Details

Under the terms of the definitive merger agreement, at the closing of the transaction, Byline will issue approximately 1.4 million shares of common stock and $28.9 million in cash to Illinois State Bancorp, Inc. shareholders. In addition, Byline will pay approximately $5.1 million in cash in connection with the settlement of all outstanding stock options.

Based upon the closing price of Byline’s common stock of $37.63 on October 5, 2026, this represents a fully diluted transaction value of approximately $87.9 million or $261.23 per Illinois State Bancorp common share.

The transaction has been approved unanimously by each company’s board of directors and is expected to close during the first quarter of 2027, and is subject to regulatory approvals, the approval of Illinois State Bancorp, Inc.’s shareholders, and the satisfaction of certain other closing conditions.

Vedder Price P.C. served as Byline’s legal advisor. D.A. Davidson & Co. served as financial advisor to Illinois State Bancorp, and Barack Ferrazzano Kirschbaum & Nagelberg LLP served as Illinois State Bancorp’s legal advisor.

Presentation

A slide presentation relating to the transaction can be accessed on the “News and Events” page of Byline’s website at www.bylinebancorp.com.

About Byline Bancorp, Inc.

Headquartered in Chicago, Byline Bancorp, Inc. is the parent company of Byline Bank, a full-service commercial bank serving small- and medium-sized businesses, financial sponsors, and consumers. Byline Bank has approximately $9.9 billion in assets and operates 44 branch locations throughout the Chicago and Milwaukee metropolitan areas. Byline Bank offers a broad range of commercial and community banking products and services including small ticket equipment leasing solutions and is one of the top Small Business Administration lenders in the United States.

About Illinois State Bancorp, Inc.

Illinois State Bancorp, Inc. is the parent company of First Nations Bank and The Bank of Bourbonnais, two full-service community banks serving individuals, businesses, and municipalities throughout the Chicago metropolitan area and Kankakee County. Through its banking subsidiaries, the company provides a broad range of commercial and consumer banking services from its headquarters in Chicago, Illinois, and Bourbonnais, Illinois. Founded in 1991, Illinois State Bancorp has built a long-standing reputation for relationship-driven community banking, helping local businesses and families achieve their financial goals for more than 35 years. For more information, visit www.fnbwbank.com and www.bourbonnais.bank.

Forward-Looking Statements

‘‘may’’, ‘‘might’’, ‘‘should’’, ‘‘could’’, ‘‘predict’’, ‘‘potential’’, ‘‘believe’’, ‘‘expect’’, ‘‘continue’’, ‘‘will’’, ‘‘anticipate’’, ‘‘seek’’, ‘‘estimate’’, ‘‘intend’’, ‘‘plan’’, ‘‘projection’’, ‘‘would’’, ‘‘annualized’’, “target” and ‘‘outlook’’, or the negative version of those words or other comparable words or phrases of a future or forward-looking nature. Accordingly, these statements involve estimates and known and unknown risks, and reflect various assumptions and involve elements of judgment and analysis, which may or may not prove to be correct, and which are subject to uncertainties and contingencies outside the control of Byline which could cause actual results to differ materially from those expressed in this communication. No representations, warranties or guarantees are or will be made by Byline as to the reliability, accuracy or completeness of any forward-looking statements contained in this communication or that such forward-looking statements are or will remain based on reasonable assumptions. You should not place undue reliance on any forward-looking statements contained in this communication.

Important Additional Information and Where to Find It

This communication is being made in respect of the proposed merger transaction involving Byline and Illinois State Bancorp. Byline intends to file a registration statement on Form S-4 with the SEC, which will include a proxy statement of Illinois State Bancorp and a prospectus of Byline, and Byline will file other documents regarding the proposed transaction with the SEC. A definitive proxy statement/prospectus will also be sent to Illinois State Bancorp shareholders seeking the required shareholder approval of the proposed transaction. This press release is not a substitute for the proxy statement/prospectus or the registration statement or for any other document that Byline may file with the SEC and send to Illinois State Bancorp’s shareholders in connection with the proposed transaction. Before making any voting or investment decision, investors and security holders of Illinois State Bancorp are urged to carefully read the entire registration statement and proxy statement/prospectus, when they become available, as well as any amendments or supplements to these documents, because they will contain important information about the proposed transaction. The documents filed by Byline with the SEC may be obtained free of charge at the SEC’s website at www.sec.gov. In addition, the documents filed by Byline may be obtained free of charge at its website at http://www.bylinebancorp.com/Docs. Alternatively, these documents, when available, can be obtained free of

charge from Byline upon written request to Byline Bancorp, Inc., Attn: Brian F. Doran, General Counsel & Corporate Secretary, 180 North LaSalle Street, 3rd Floor, Chicago, Illinois 60601, or by calling (773) 244-7000.

Participants in this Transaction

Byline, Illinois State Bancorp, their respective directors and executive officers and certain of their other members of management and employees may be deemed to be participants in the solicitation of proxies from Illinois State Bancorp shareholders in connection with the proposed transaction. Information about the directors and executive officers of Byline may be found in Byline’s Annual Report on Form 10-K for the year ended December 31, 2025, as filed with the SEC on February 27, 2026, and in Byline’s proxy statement for its 2026 Annual Meeting of Stockholders, as filed with the SEC on April 20, 2026, copies of which can be obtained free of charge from Byline or from the SEC’s website as indicated above. To the extent the holdings of Byline’s securities by its directors and executive officers have changed since the amounts set forth in Byline’s proxy statement for its 2026 Annual Meeting of Stockholders, such changes have been or will be reflected on Statements of Change in Ownership on Form 4 filed with the SEC. In addition, information about the directors and executive officers of Byline and Illinois State Bancorp and other persons who may be deemed participants in the transaction will be included in the proxy statement/prospectus and other relevant materials when filed with the SEC.

No Offer or Solicitation

Communications in this press release do not constitute an offer to sell or the solicitation of an offer to subscribe for or buy any securities or a solicitation of any vote or approval with respect to the proposed transaction or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction.

Contact For Byline Bancorp, Inc.:

Investors / Media:

Brooks O. Rennie

Head of Investor Relations

Byline Bancorp, Inc.

(312) 660-5805

brennie@bylinebank.com

Contact For Illinois State Bancorp, Inc.:

Investors / Media:

Florian J. Barbi

Chairman, President & CEO

Illinois State Bancorp, Inc.

(773) 594-5900

Florian.barbi@fnbwbank.com

EX-99.2

Filename: by-ex99_2.htm · Sequence: 3

Investor Presentation October 6, 2026 Byline Bancorp, Inc. to Acquire Illinois State Bancorp, Inc. Exhibit 99.2

Important Notices BYLINE BANCORP, INC. | ILLINOIS STATE BANCORP, INC. FORWARD-LOOKING STATEMENTS The information included herein may contain “forward-looking statements” within the meaning of the U.S. federal securities laws. Any statements about Byline Bancorp, Inc. (“Byline”) expectations, beliefs, plans, strategies, predictions, forecasts, objectives or assumptions of future events or performance are not historical facts and may be forward-looking. These statements include, but are not limited to, the expected completion date, financial benefits and other effects of the proposed merger of Byline and Illinois State Bancorp, Inc. (“Illinois State Bancorp”). These statements are often, but not always, made through the use of words or phrases such as “anticipates,” “believes,” “expects,” “can,” “could,” “may,” “predicts,” “potential,” “opportunity,” “should,” “will,” “estimate,” “plans,” “projects,” “continuing,” “ongoing,” “seeks,” “intends” and similar words or phrases. Accordingly, these statements involve estimates, known and unknown risks, assumptions and uncertainties that could cause actual strategies, actions or results to differ materially from those expressed in them, and are not guarantees of timing, future results or other events or performance. Because forward-looking statements are necessarily only estimates of future strategies, actions or results, based on management’s current expectations, assumptions and estimates on the date hereof, there can be no assurance that actual strategies, actions or results will not differ materially from expectations, and readers are cautioned not to place undue reliance on such statements. Factors that may cause such a difference include, but are not limited to, the reaction to the transaction of the companies’ customers, employees and counterparties; customer disintermediation; inflation; changes in interest rates; expected synergies, cost savings and other financial benefits of the proposed transaction might not be realized within the expected timeframes or might be less than projected; the requisite shareholder and regulatory approvals for the proposed transaction might not be obtained; credit and interest rate risks associated with Byline’s and Illinois State Bancorp’s respective businesses, customers, borrowings, repayment, investment, and deposit practices; general economic conditions, either nationally or in the market areas in which Byline and Illinois State Bancorp operate or anticipate doing business, are less favorable than expected; new regulatory or legal requirements or obligations; and other risks. Certain risks and important factors that could affect Byline’s future results are identified in its Annual Report on Form 10-K for the year ended December 31, 2025 and other reports filed with the Securities and Exchange Commission (“SEC”), including among other things under the heading “Risk Factors” in such Annual Report on Form 10-K. Any forward-looking statement speaks only as of the date on which it is made, and Byline undertakes no obligation to update any forward-looking statement, whether to reflect events or circumstances after the date on which the statement is made, to reflect new information or the occurrence of unanticipated events, or otherwise. Due to rounding, numbers presented throughout this document may not add up precisely to the totals provided and percentages may not precisely reflect the absolute figures. IMPORTANT ADDITIONAL INFORMATION AND WHERE TO FIND IT This communication is being made in respect of the proposed merger transaction involving Byline and Illinois State Bancorp, Inc. Byline intends to file a registration statement on Form S-4 with the Securities and Exchange Commission (the “SEC”), which will include a proxy statement of Illinois State Bancorp and a prospectus of Byline, and Byline will file other documents regarding the proposed transaction with the SEC. A definitive proxy statement/prospectus will also be sent to Illinois State Bancorp shareholders seeking approval of the proposed transaction. Before making any voting or investment decision, investors and security holders of Illinois State Bancorp are urged to carefully read the entire registration statement and proxy statement/prospectus, when they become available, as well as any amendments or supplements to these documents, because they will contain important information about the proposed transaction. The documents filed by Byline with the SEC may be obtained free of charge at the SEC’s website at www.sec.gov. In addition, the documents filed by Byline may be obtained free of charge at its website at http://www.bylinebancorp.com/Docs. Alternatively, these documents, when available, can be obtained free of charge from Byline upon written request to Byline Bancorp, Inc., Attn: Brian F. Doran, General Counsel & Corporate Secretary, 180 North LaSalle Street, 3rd Floor, Chicago, Illinois 60601, or by calling (773) 244-7000. PARTICIPANTS IN THE SOLICITATION Byline, Illinois State Bancorp, their respective directors and executive officers and certain of their other members of management and employees may be deemed to be participants in the solicitation of proxies from Illinois State Bancorp’s shareholders in connection with the proposed transaction. Information about the directors and executive officers of Byline may be found in Byline’s Annual Report on Form 10-K for the year ended December 31, 2025, as filed with the SEC on February 27, 2026, and in Byline’s proxy statement for its 2026 Annual Meeting, as filed with the SEC on April 20, 2026, copies of which can be obtained free of charge from Byline or from the SEC’s website as indicated above. In addition, information about the directors and executive officers of Byline and Illinois State Bancorp and other persons who may be deemed participants in the transaction will be included in the proxy statement/prospectus and other relevant materials when filed with the SEC. NO OFFER OR SOLICITATION This communication does not constitute an offer to sell or the solicitation of an offer to subscribe for or buy any securities or a solicitation of any vote or approval with respect to the proposed transaction or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction.

Overview of Illinois State Bancorp, Inc. BYLINE BANCORP, INC. | ILLINOIS STATE BANCORP, INC. COMPANY OVERVIEW A privately held, Chicago-based bank holding company Operates through two community banking subsidiaries, each with 50+ years of history: First Nations Bank (Chicago, IL) The Bank of Bourbonnais (Bourbonnais, IL) Serves customers through two business lines: community and commercial banking Seasoned commercial lending team with deep local market relationships FINANCIAL HIGHLIGHTS SIZE $617 Million TOTAL ASSETS $471 Million TOTAL LOANS & LEASES $511 Million TOTAL DEPOSITS FINANCIAL PERFORMANCE $6.7 Million NET INCOME 92.2% LOAN / DEPOSIT RATIO 0.08% NPAs / ASSETS LOAN & DEPOSIT COMPOSITION(2) LOANS Yield on loans: 6.08% Non-Owner Occ. CRE Owner Occ. CRE C&D 1 - 4 Family Multifamily C&I Other DEPOSITS Cost of deposits: 2.51% Noninterest-bearing Deposits Jumbo Time Deposits IB Demand, Savings & MMDA Retail Time Deposits CHICAGO FOOTPRINT Source: S&P Global Market Intelligence and Company financials. Note: Financial data as of 6/30/2026. (1) Data based on last twelve months (LTM). (2) Data based on combined bank-level regulatory data as of the quarter ended 6/30/2026. Byline (44) Illinois State Bancorp (4) (1)

Overview of Transaction and Consideration Terms Financially attractive transaction with compelling pro forma financial impact BYLINE BANCORP, INC. | ILLINOIS STATE BANCORP, INC. Consideration Byline Bancorp, Inc. (NYSE: BY) will acquire 100% of Illinois State Bancorp, Inc. outstanding common stock Byline to issue approximately 1.4 million shares of common stock and $28.9 million in cash to Illinois State Bancorp, Inc. shareholders Fixed exchange ratio of 4.5208 Byline shares for each Illinois State Bancorp common share outstanding Byline to pay approximately $5.1 million in cash to settle all outstanding stock options Based upon Byline closing stock price of $37.63, this equates to an aggregate transaction value of $87.9 million or $261.23 per share(1) Transaction Multiples Price / TBV: 1.07x(1) Core Deposit Premium: 1.6%(1) LTM Earnings: 13.1x(1) Pro Forma Impacts Minimal TBV dilution of 1.2%, with earnback expected in less than 1.5 years Mid-single digit EPS accretion Projected IRR exceeds Byline’s cost of capital hurdles Timing & Approvals Subject to Illinois State Bancorp, Inc. shareholder approval Customary regulatory approvals Anticipated closing in 1Q27 Note: All multiples for transaction are based on financial data as of 6/30/2026. (1) Based on Byline Bancorp closing stock price of $37.63 as of 10/5/2026.

Key Transaction Assumptions Detailed financial, legal, regulatory and operational due diligence performed BYLINE BANCORP, INC. | ILLINOIS STATE BANCORP, INC. Balance Sheet Marks Estimated gross credit mark of approximately 3.7% Loan interest rate mark of 2.0% Other net marks of $0.9 million Synergies Significant cost savings expected to be realized as part of the transaction Approximately 75% realization in 2027, 100% in 2028 and thereafter Merger Costs Expected to be approximately $16.6 million pre-tax Other Assumptions Core Deposit Intangible: ~3.0% of non-jumbo deposits, amortized over 7 years utilizing the sum-of-years digits method Diligence Process Conducted detailed financial, legal, regulatory and operational due diligence Experienced Acquirer In market transaction by a disciplined and proven acquirer with five whole-bank acquisitions since 2016

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Document And Entity Information

Oct. 06, 2026

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BYLINE BANCORP, INC.

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Pre-commencement Tender Offer

false

Pre-commencement Issuer Tender Offer

false

Title of 12(b) Security

Common Stock

Trading Symbol

Security Exchange Name

NYSE

- Definition

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

+ References

No definition available.

+ Details

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dei_AmendmentFlag

Namespace Prefix:

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Data Type:

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Balance Type:

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- Definition

Area code of city

+ References

No definition available.

+ Details

Name:

dei_CityAreaCode

Namespace Prefix:

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Data Type:

xbrli:normalizedStringItemType

Balance Type:

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- Definition

Cover page.

+ References

No definition available.

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Name:

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Data Type:

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- 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:

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Data Type:

xbrli:normalizedStringItemType

Balance Type:

Period Type:

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- 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:

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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

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Name:

dei_EntityCentralIndexKey

Namespace Prefix:

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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

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Name:

dei_EntityEmergingGrowthCompany

Namespace Prefix:

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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

Former Legal or Registered Name of an entity

+ References

No definition available.

+ Details

Name:

dei_EntityInformationFormerLegalOrRegisteredName

Namespace Prefix:

dei_

Data Type:

xbrli:normalizedStringItemType

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:

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Data Type:

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Balance Type:

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- 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:

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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:

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- 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:

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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

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Namespace Prefix:

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Data Type:

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Balance Type:

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- 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

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Name:

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Namespace Prefix:

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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:

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Data Type:

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Balance Type:

Period Type:

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- 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:

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Data Type:

xbrli:booleanItemType

Balance Type:

Period Type:

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- Definition

Trading symbol of an instrument as listed on an exchange.

+ References

No definition available.

+ Details

Name:

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Namespace Prefix:

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Data Type:

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Balance Type:

Period Type:

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- 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

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