FNB BANCORP

12 South1 East Main Street, American Fork, Utah 84003

Layton Utah 84041

NOTICE OF SPECIAL MEETING OF SHAREHOLDERS OF

TO BE HELD APRIL 18, 2019ALTABANCORP^TM

TO THE SHAREHOLDERS OF FNB BANCORP:[    ], 2021

To the Shareholders of Altabancorp:

A special meeting of the shareholders of FNB BancorpAltabancorp (“FNB”AB”) will be held on April 18, 2019, at 10:00 a.m. Mountain Time, at the Davis Conference Center located at 1651 North 700 West, Layton, Utah 84041.[___], 2021. The special meeting will be held in a virtual meeting format only. Please visit the website www.proxydocs.com/ALTAand enter your control number to register to attend the meeting. The deadline to register to attend the virtual special meeting is [__], 2021, at 5:00 p.m. Mountain Time. You are encouraged to vote your shares by telephone, by completing and mailing the enclosed form of proxy, or online in advance of the special meeting but may also vote during the meeting by following the instructions available on the meeting website. The special meeting will convene at [___] Mountain Time for the following purposes:

Holders of record of FNBAB common stockshares at the close of business on March 6, 2019,[___], 2021, the record date for the special meeting, are entitled to notice of and to vote at the special meeting or any adjournments or postponements of it. The affirmative vote of the holders of at least a majority of the outstanding shares of FNB’s outstandingAB’s common stock entitled to vote is required for approval of the merger agreement. To that end, FNB’sAB’s directors and executive officers and certain significant shareholders have signed agreements to vote their shares in favor of the merger agreement. SuchAs of the record date, such persons arewere entitled to vote 1,357,605[_________] shares representing approximately 42.95%[____]% of all outstanding shares of FNBAB common stock.shares. As of March 6, 2019,the record date, there were 3,160,969[__________] AB common shares of FNB common stock outstanding.

Your vote is important. Whether or not you plan to attendparticipate in the special meeting please complete, sign, datevirtually, we encourage you to submit a proxy to vote your shares as promptly as possible in order to make certain that you are represented at the meeting. You may submit a proxy over the Internet, as well as by telephone or by completing, signing, dating and promptly returnreturning the accompanying proxy using the enclosed envelope. If for any reason you should desire to revoke your proxy, you may do so at any time before it is voted at the meeting.If you do not vote your shares, it will have the same effect as voting against the merger.

The board of directors of FNBAB has determined that the merger agreement is fair to, advisable, and in the best interests of FNBAB and its shareholders and unanimously recommends that you vote FOR approval of the merger agreement.agreement, FOR approval of the merger-related named executive officer compensation proposal, and FOR approval of the adjournment proposal. With regard to its recommendation that shareholders vote FOR approval of the merger agreement, the board of directors of FNBAB considered a number of factors, as discussed in “ Background“Background of and Reasons for the Merger” beginning on page 18.26. Such factors also constituted the reasons that the board of directors determined to approve the merger agreement and to recommend that FNBAB shareholders vote in favor of the merger agreement.

You will receive instructions on howImportant Notice Regarding the Availability of Proxy Materials for the

Special Shareholders Meeting to exchange your sharesbe held [____] 2021:

The proxy statement and notice of FNB common stock for the merger consideration promptly after the closing of the merger.special meeting are available at www.proxydocs.com/ALTA or from our Investor Relations website at www.altabancorp.com.

Layton, Utah

March 13, 2019

provided on the Glacier and AB websites is not part of this proxy statement/prospectus and is not incorporated herein by reference. Copies of the documents that Glacier or AB, respectively, files with the SEC can also be obtained, free of charge, by directing a written request to Glacier Bancorp, Inc., 49 Commons Loop, Kalispell, Montana 59901, ATTN: Corporate Secretary or to Altabancorp, 1 East Main Street, American Fork, Utah 84003, ATTN: Corporate Secretary.

Glacier has filed a registration statement on Form S-4 to register with the SEC Glacier common shares as specified therein. This proxy statement/prospectus is a part of that registration statement. As permitted by SEC rules, this document does not contain all of the information included in the registration statement or in the exhibits or schedules to the registration statement. You may read and copy the registration statement, including any amendments, schedules and exhibits, at the addresses set forth below. Statements contained in this document as to the contents of any contract or other documents referred to in this document are not necessarily complete. In each case, you should refer to the copy of the applicable contract or other document filed as an exhibit to the registration statement. This document incorporates important business and financial information about Glacier fromand AB that is not included in or delivered with this document, including incorporating by reference documents that Glacier hasand AB have previously filed with the SecuritiesSEC. These documents contain important information about the companies and Exchange Commission (“SEC”) and that are contained in or incorporated by reference into this proxy statement/prospectus. For a listing of Glacier documents incorporated by reference into this proxy statement/prospectus, please see the section entitledtheir financial condition. See “Where You Can Find More Information.” This information isThese documents are available for you to review at the SEC’s website athttp://www.sec.gov.

You may request copies of this proxy statement/prospectus and any of the documents incorporated by reference into this proxy statement/prospectus or other information concerning Glacier, without charge byto you upon written or oral request to the applicable company’s principal executive offices. The respective addresses and telephone or writtennumbers of such principal executive offices are listed below:

To obtain timely delivery of these documents, you must request directed to:

Glacier Bancorp, Inc.

49 Commons Loop

Kalispell, Montana 59901

ATTN: Ron Copher, Corporate Secretary

Telephone: (406)751-7706

Certain reports can also be found on Glacier’s website atwww.glacierbancorp.com.

Glacier’s common stock is traded on the NASDAQ Global Select Market under the symbol “GBCI.”

You will not be charged for the documents that you request.If you would like to request documents, please do so by April 11, 2019information no later than [    ], 2021, in order to receive them before the FNB special shareholders’ meeting.meeting of AB shareholders (the “AB special meeting”).

FNB

FNB does not have a class of securities registeredGlacier common shares, par value $0.01 per share, are traded on the Nasdaq Global Select Market, under Section 12 of the Securities Exchange Act of 1934 (the “Exchange Act”), is not subject tosymbol “GBCI,” and AB common shares, par value $0.01 per share, are traded on The Nasdaq Capital Market under the reporting requirements of Section 13(a) or 15(d) of the Exchange Act, and accordingly does not file documents or reports with the SEC.

If you have questions concerning the merger or this proxy statement/prospectus, would like additional copies of this proxy statement/prospectus, would like copies of FNB’s articles of incorporation or bylaws, or would like copies of FNB’s historical consolidated financial statements or need help voting your shares, please contact:

FNB Bancorp

12 South Main

Layton, Utah 84041

ATTN: Nic Bement

(801)813-1600symbol “ALTA.”

TABLE OF CONTENTS

Appendix A – Plan and Agreement of Merger, dated as of May 18, 2021

Appendix B – Opinion of Keefe, Bruyette & Woods, Inc., Financial Advisor to Altabancorp

i

QUESTIONS AND ANSWERS

Why am I receiving these materials?

We are sending you these materials to solicit your proxy to vote in favor of the merger and to help you decide how to vote your shares of FNB BancorpAltabancorp (“FNB”AB”) common stock with respect to its proposed merger with Glacier Bancorp, Inc. (“Glacier”). The merger cannot be completed unless FNBAB receives the affirmative vote of the holders of at least a majority of the outstanding shares of FNB’sAB’s common stock. FNBstock entitled to vote on the matter. AB is holding a special meeting of shareholders to vote on proposals relating to the merger. Information about the special meeting is contained in this document. See “FNB“AB Special Shareholders Meeting.”

This document is both a proxy statement of FNBAB and a prospectus of Glacier. It is a proxy statement because the officers and board of directors of FNBAB (the “FNB“AB Board”) are soliciting proxies from FNBAB’s shareholders in connection with voting on the merger. It is a prospectus because Glacier will issue shares of its common stock in exchange for AB common shares of FNB common stock as the consideration to be paid in the merger.

What will FNBhappen in the merger?

In the proposed merger, AB will merge with and into Glacier, with Glacier surviving the merger. Immediately following the merger, Altabank (the “Bank”) will be merged into Glacier’s subsidiary Glacier Bank. Shares of Glacier will continue to trade on The Nasdaq Global Select Market, with the trading symbol “GBCI.”

What will AB shareholders receive in the merger?

Under the terms of the merger agreement, each AB common share (including each share to be issued upon settlement of FNB commoneach unvested restricted stock unit (“RSU”)) will be exchanged for 0.64740.7971 shares of Glacier common stock (the “per share stock consideration”), subject to adjustment as described below.certain adjustments, with cash paid in lieu of fractional shares.

Assuming for purposes of illustration only that the average closing price for Glacier common stock is $41.06$[___] (which was the closing price forof Glacier common stock on March 11, 2019)[___], and that there is no reduction in the exchange ratio due to the FNB Closing Capital (discussed below) being less than the required amount,2021), each share of FNBAB common stockshare would be exchanged for 0.7971 shares of Glacier common stock with a total value equal to $26.58.

If the FNB Closing Capital (as defined in the merger agreement) exceeds $39,285,000, subject to certain adjustments, FNB may, upon written notice to Glacier and effective immediately prior to the closing of the merger, declare and pay a special dividend to its shareholders in the amount of such excess.

If the FNB Closing Capital is less than $39,285,000, the total number of Glacier shares issued in the merger will be reduced by a number of shares equal in value to the differential between $39,285,000 and the actual FNB Closing Capital.$[___].

The amount of Glacier commonper share stock exchanged for each share of FNB common stockconsideration may also be adjusted in certain circumstances ifbased on whether Glacier common stock is trading either higher or lower than prices specified in the merger agreement immediately prior to the closing of the merger, in order to avoid termination of the merger agreementagreement.

In addition, the per share stock consideration will be subject to reduction if the “AB Closing Capital,” as follows:

described above, AB shareholders will own,receive an estimated 15,129,749 shares of Glacier common stock in the aggregate,merger, representing approximately 2.36%13.7% of Glacier’s outstanding common stock followingafter taking into account Glacier shares to be issued in the merger.

How are outstanding AB stock options and RSUs addressed in the merger agreement?

Under the terms of the merger agreement, when the merger agreement becomes effective (the “effective time”), each outstanding RSU under the People’s Utah Bancorp 2014 Incentive Plan, the Altabancorp 2020 Equity Incentive Plan and the People’s Utah Bancorp Amended and Restated 2008 Stock Incentive Plan (the “AB Stock Plans”) will automatically vest and be settled, and each AB common share issued as a result will have the right to receive the per share stock consideration and cash in lieu of fractional AB common shares. Outstanding options to purchase AB common shares under the AB Stock Plans (the “AB Options”), whether vested or unvested, will be automatically canceled at the effective time, and the holders of AB Options will be paid in cash an amount per share equal to the spread, if any, between (a) the product of the Glacier average closing price (as defined in the merger agreement) multiplied by the per share stock consideration and (b) the exercise price per share of such AB Option, net of any cash which must be withheld under applicable tax laws. Any AB Option that has an exercise price per share that is greater than the total consideration value per share will be cancelled without any payment.

Will I receive any fractional shares of Glacier common stock as part of the merger consideration?

No. Glacier will not issue any fractional shares of Glacier common stock in the merger. Instead, Glacier will pay you the cash value of a fractional share (without interest) in an amount determined by multiplying the fractional share interest to which you would otherwise be entitled by the average of the closing sales prices of one share of Glacier common stock on The Nasdaq Global Select Market for the 20 trading days ending on the tenth business day immediately preceding the effective date of the merger.

How soon after the merger is completed can I expect to receive my merger consideration?

Glacier will work with its exchange agent, American Stock Transfer & Trust Company, LLC, to distributecomplete the exchange of your AB stock certificates for consideration payable in the merger as promptly as practicable following the completion of the merger.

Will I be able to trade the shares of Glacier common stock that I receive in the merger bemerger?

You may freely transferable?

Yes. Thetrade the shares of Glacier common stock issued in the merger, will be transferable freeunless you are an “affiliate” of restrictionsGlacier as defined by Rule 144 under federalthe Securities Act of 1933, as amended. Affiliates consist of individuals or entities that control, are controlled by or are under the common control with Glacier, and state securities laws.include the executive officers and directors of Glacier after the merger and may include significant shareholders of Glacier.

When will the merger occur?

We presently expect to complete the merger during the secondfourth quarter of 2019.2021. The actual timing of the transaction is subject to a number of factors (primarily regulatory approvals), many of which are beyond the control of Glacier and FNB.AB. The merger is conditioned upon and will occur after the approval of the merger agreement by the affirmative vote of holders of at least a majority of the outstanding AB common shares of FNB common stock,entitled to vote on the matter at the AB special meeting, after the merger has received regulatory approvals, and following the satisfaction or waiver of the other conditions to the merger described in the merger agreement and summarized under “The Merger” below.

The merger agreement provides that in the event the closing has not occurred by November 30, 2021, the first date on which the closing may occur is January 31, 2022.

If the merger does not occur by September 30, 2019,February 28, 2022, either Glacier or FNBAB may unilaterally terminate the merger agreement. However, if as of September 30, 2019, the condition to closing thatFebruary 28, 2022, all required governmental regulatory approvals have been obtained has not been satisfied,obtained, then the deadline for closingconsummation of the merger will be extended to on or before NovemberApril 30, 2019,2022, if either Glacier or AB notifies FNBthe other party in writing on or prior to September 30, 2019February 28, 2022, of its election to extend such closing deadline.date.

When and where will the special meeting take place?

FNBAB will hold a special meeting of its shareholders on April 18, 2019,[___], 2021, at 10:[___] Mountain Time. The special meeting will be held in virtual meeting format only. In order to attend the special meeting, AB shareholders must register at www.proxydocs.com/ALTA by 5:00 a.m.p.m. Mountain Time at the Davis Conference Center located at 1651 North 700 West, Layton, Utah 84041.on [__], 2021.

You may cast your vote by submitting a proxy through the Internet or by telephone by following the instructions included on the enclosed proxy card or by mail by completing, signing and dating the enclosed proxy card and returning it to us promptly in the enclosed envelope. ReturningSubmitting a proxy through the Internet or by telephone or returning the proxy card will not affect your right to attend the special meeting by virtual means and vote.

If you choose to vote your shares at the virtual special meeting, you should follow the instructions available on the shareholder meeting website.

If your shares are registered in person“street name” in the name of a broker or other nominee and you wish to vote at the special meeting, please bringyou will need to obtain a legal proxy from your bank or brokerage firm. Please consult the enclosedvoting form sent to you by your bank or broker to determine how to obtain a legal proxy in order to vote at the meeting.

What if I fail to submit a proxy or to instruct my broker, bank or other nominee?

If you fail to properly submit a proxy or to instruct your broker, bank or other nominee to vote your AB common shares, and you do not attend the special meeting and vote your shares, your shares will not be voted. This will have the same effect as a vote “AGAINST” approval of the merger agreement, but will have no impact on the outcome of the other proposals.

Can I attend the special meeting and vote my shares at the meeting?

Yes. Although the AB Board requests that you submit a proxy through the Internet, by telephone or by returning the proxy card and proofaccompanying this proxy statement/prospectus, all shareholders are invited to attend the shareholder meeting. Shareholders of identification.record on [__________], 2021 can vote at the special meeting by following the instructions available on the meeting website.

Can I change my vote after I have mailedsubmitted my signed proxy card?proxy?

Yes. YouIf you do not hold your shares in “street name,” there are three ways you may change your vote at any time after you have submitted your proxy and before your proxy is voted at the special meeting. If your shares of FNB common stock are held in your own name, you may change your vote as follows:meeting:

If my shares are held in “street name” by my broker, bank or other nominee, will my broker, bank or other nominee automatically vote my shares for me?

No. Your broker, bank or other nominee will not vote your shares unless you provide instructions to your broker, bank or other nominee on how to vote. You should instruct your broker, bank or other nominee to vote your shares by following the instructions provided by the broker, bank or nominee with this proxy statement/prospectus.

How does the FNBAB Board recommend that I vote?

The FNBAB Board unanimously recommends that FNBAB shareholders vote “FOR” the proposals described in this proxy statement/prospectus, including in favor of approval of the merger agreement.agreement and the merger-related named executive compensation proposal.

What do I need to do now?

We encourage you to read this proxy statement/prospectus and related information in its entirety. Important information is presented in greater detail elsewhere in this document, and documents governing the merger are attached as appendices to this proxy statement/prospectus. In addition, much of the business and financial information about Glacier that may be important to you is incorporated by reference into this document from documents separately filed by Glacier with the Securities and Exchange Commission (“SEC”). This means that important disclosure obligations to you are satisfied by referring you to one or more documents separately filed with the SEC.

Following review of this proxy statement/prospectus,please complete, sign,submit a proxy through the Internet, by telephone or by completing, signing, and datedating the enclosed proxy card and return it in the enclosed envelopeas soon as possible so that your shares of FNBAB common stockshares can be voted at FNB’sAB’s special meeting of shareholders.

What happens if I sell my shares after the record date but before the special meeting?

The record date of the special meeting is earlier than the date of the special meeting and the date that the merger is expected to be completed. If you sell or otherwise transfer your shares after the record date, but before the date of the special meeting, you will retain your right to vote at the special meeting, but you will not have the right to receive the merger consideration to be received by shareholders in the merger. In order to receive the merger consideration, a shareholder must hold his or her shares through completion of the merger.

What do I do if I receive more than one proxy statement/prospectus or set of voting instructions?

If you hold shares directly as a record holder and also in “street name” or otherwise through a nominee, you may receive more than one proxy statement/prospectus and/or set of voting instructions relating to the special meeting. These should each be voted and/or returned separately in order to ensure that all of your shares are voted.

Should I send in my common stock certificates now?

No.Please do not send your FNBAB common stockshare certificates with your proxy card. You will receive written instructions from Glacier’s exchange agent promptly following the closing of the merger on how to exchange your FNBAB common stockshare certificates for the merger consideration.

What risks should I consider?consider in deciding whether to vote for approval of the merger agreement?

You should review carefully our discussion under “Risk Factors.” You should also review the factors considered by the FNBAB Board in approving the merger agreement. See “Background of and Reasons for the Merger.”

What are the material United States federal income tax consequences of the merger to FNBAB shareholders?

Glacier and FNB expect to reportAB intend for the merger of FNB with and into Glacierto qualify as atax-free reorganization for U.S. federal income tax purposes under “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”). It is a condition to the closing ofIf the merger that Miller Nash Graham & Dunn LLP, tax counsel to Glacier, deliver an opinion addressed to Glacier and FNB that the merger will qualifyqualifies as a reorganization underwithin the meaning of Section 368(a).

RISK FACTORS

In addition to the other information contained in or incorporated by reference into this document, including the matters addressed under the caption “Cautionary Note Regarding Forward-Looking Statements,” you should consider the matters described below carefully in determining whether or not to approve the merger agreement and the transactions contemplated by the merger agreement.

Risks Associated with the Proposed Merger

Because you are receiving a fixed number of shares (subject to adjustment) and the market price of the Glacier common stock may fluctuate, you cannot be sure of the value of the shares of Glacier common stock that you will receive.

At the time of the FNBAB special shareholder meeting, and prior to the closing of the merger, you will not be able to determine the value of the Glacier common stock that you will receive upon completion of the merger. Any change in the market price of Glacier common stock prior to completion of the merger will affect the value of the consideration that FNBAB shareholders will receive in the merger. Common stock price changes may result from a variety of factors, including but not limited to general market and economic conditions, changes in Glacier’s business, operations and prospects, and regulatory considerations. Many of these factors are beyond the control of Glacier or FNB. On March 11, 2019, the closing price of Glacier common stock was $41.06.AB. You should obtain current market prices for Glacier common stock.

The merger agreement provides that the number of shares of Glacier common stock to be issued for each share of FNBAB common stockshare in the merger may be decreased or increased, as the case may be, if the average closing price of Glacier common stock, determined pursuant to the merger agreement, is greater than or less than specified prices. If Glacier’s average closing price determined in accordance with the merger agreement is greater than $46.63$74.15 and Glacier elects to terminate the merger agreement, the FNBAB Board wouldcould determine, without resoliciting the vote of FNBAB shareholders, whether or not to accept a decrease on aper-share basis in the number of shares of Glacier common stock to be issued in the merger to avoid such termination. See “The Merger – Termination of the Merger Agreement.”

The results of operations of Glacier after the merger may be affected by factors different from those currently affecting the results of operations of AB.

The businesses of Glacier and AB differ in certain respects and, accordingly, the results of operations of the combined company and the market price of the combined company’s common shares may be affected by factors different from those currently affecting the independent results of operations of AB and Glacier. For a discussion of the business of Glacier and certain factors to be considered in connection with Glacier’s business, see “Information Concerning Glacier” and the documents incorporated by reference in this document and referred to under “Where You Can Find More Information.” For a discussion of the business of AB and certain factors to be considered in connection with AB’s business, see “Information Concerning Altabancorp” and the documents incorporated by reference in this document and referred to under “Where You Can Find More Information.”

The merger agreement limits FNB’sAB’s ability to pursue other transactions and provides for the payment of abreak-up fee if FNBAB does so.

While the merger agreement is in effect, subject to very narrow exceptions, FNBAB and its directors, officers, employees, agents and representatives are prohibited from initiating or encouraging inquiries with respect to alternative acquisition proposals. The prohibition limits FNB’sAB’s ability to seek offers from other potential acquirers that may be superior from a financial point of view to the proposed transaction. If FNBAB receives an unsolicited proposal from a third party that is superior from a financial point of view to that made by Glacier and the merger agreement is terminated, FNBAB will be required to pay a $3,200,000$35,000,000 break-up fee. This fee makes it less likely that a third party will make an alternative acquisition proposal. See “The Merger –Break-Up Fee.”

Combining ourthe two companies may be more challenging, costly or time-consuming than we expect.expected.

Glacier and FNBAB have operated and, until the completion of the merger, will continue to operate, independently. Although Glacier has successfully completed numerous mergers in the recent past, this is a larger transaction than others and regardless it is possible that the integration of the Bank into Glacier Bank could result in the loss of key employees, the disruption of the ongoing business of the Bank or inconsistencies in standards, controls, procedures and policies that adversely affect ourthe Bank’s ability to maintain relationships with customers and employees or to achieve the anticipated benefits of the merger. As with any merger of banking institutions, there also may be disruptions that cause usthe Bank to lose customers or cause customers to take their deposits out of the Bank.

After the merger is completed, FNBAB shareholders will become Glacier shareholders and will have different rights that may be less advantageous than their current rights.

Upon completion of the merger, FNBAB shareholders will become Glacier shareholders. Differences in FNB’sAB’s articles and FNB’sAB’s bylaws and Glacier’s articles and Glacier’s bylaws will result in changes to the rights of FNBAB shareholders who become Glacier shareholders. See “Comparison of Certain Rights of Holders of Glacier and FNBAB Common Stock.Shares.”

AB’s shareholders will have a reduced ownership and voting interest after the merger and will exercise less influence over management.

AB’s shareholders currently have the right to vote in the election of the AB Board and on other significant matters affecting AB, such as the proposed merger with Glacier. When the merger occurs, each AB shareholder will become a shareholder of Glacier with a percentage ownership of the combined organization that is much smaller than the shareholder’s percentage ownership of AB. Based on the anticipated number of Glacier common shares to be issued in the merger, it is anticipated that the AB shareholders will only own approximately 13.7% of all of the outstanding shares of Glacier’s common stock following the merger. Because of this, AB’s shareholders will have less influence on the management and policies of Glacier than they now have on the management and policies of AB. Furthermore, shareholders of Glacier do not have preemptive or similar rights, and therefore, Glacier can sell additional voting securities in the future without offering them to the former AB shareholders, which would further reduce their ownership percentage in, and voting control over, Glacier.

The merger may fail to qualify as a reorganization for federal tax purposes, resulting in the recognition by AB’s shareholders of taxable gain or loss in respect of their AB shares.

Glacier and AB intend the merger to qualify as a reorganization within the meaning of Section 368(a) of the Internal Revenue Code. Glacier and AB, as a condition to closing, will each obtain an opinion from their respective legal counsel that the merger will qualify as a reorganization for federal tax purposes. These opinions do not bind the Internal Revenue Service or the courts or prevent either from taking a contrary position. Neither Glacier nor AB has requested and neither intends to request any ruling from the Internal Revenue Service as to the U.S. federal income tax consequences of the merger. Furthermore, if the merger fails to qualify as a reorganization, Glacier, as successor to AB, may incur a significant tax liability since the merger would be treated as a taxable sale of AB’s assets for U.S. federal income tax purposes.

Glacier and AB will be subject to business uncertainties and contractual restrictions while the merger is pending.

Uncertainty about the effect of the merger on employees, customers and vendors may have an adverse influence on the business, financial condition and results of operations of Glacier and AB. These uncertainties may impair Glacier’s and AB���s ability to attract, retain and motivate key personnel, maintain current deposit levels, and continue to attract depositors and attract new borrowers pending the consummation of the merger, as such personnel, depositors and borrowers may experience uncertainty about their future relationships following the consummation of the merger. Additionally, these uncertainties could cause customers (including depositors and borrowers), suppliers, vendors and others who deal with Glacier or AB to seek to change existing business relationships with Glacier, AB or the combined company or fail to extend an existing relationship with Glacier, AB or the combined company.

In addition, the merger agreement restricts AB from taking certain actions without Glacier’s consent while the merger is pending. These restrictions could have a material adverse effect on AB’s business, financial condition and results of operations. See “The Merger Agreement — Covenants” for a description of the restrictive covenants applicable to AB.

Failure to complete the merger could negatively impact the stock prices and future businesses and financial results of Glacier and AB.

If the merger is not completed, the ongoing businesses of Glacier and AB may be adversely affected, and Glacier and AB will be subject to several risks, including the following:

In addition, if the merger is not completed, Glacier and/or AB may experience negative reactions from the financial markets and from their respective customers and employees. Glacier and/or AB also could be subject to litigation related to any failure to complete the merger or to enforcement proceedings commenced against Glacier or AB to perform their respective obligations under the merger agreement. If the merger is not completed, Glacier and AB cannot assure their respective shareholders that the risks described above will not materialize and will not materially affect the business, financial results and stock prices of Glacier and/or AB.

The merger is subject to the receipt of approvals and/or waivers or non-objections from governmental authorities that may delay the date of completion of the merger or impose conditions that could have an adverse effect on Glacier.

Before the merger may be completed, various approvals, waivers or non-objections must be obtained from state and federal governmental authorities, including the Federal Deposit Insurance Corporation, the Board of Governors of the Federal Reserve System, the Commissioner of the Montana Division of Banking and Financial Institutions, and the Utah Department of Financial Institutions. Satisfying the requirements of these governmental authorities may delay the date of completion of the merger. In addition, these governmental authorities may include conditions on the completion of the merger, or require changes to the terms of the merger. While Glacier and AB do not currently expect that any such conditions or changes would result in a material adverse effect on Glacier, there can be no assurance that they will not, and such conditions or changes could have the effect of delaying completion of the merger, or imposing additional costs on or limiting the revenues of Glacier following the merger, any of which might have a material adverse effect on Glacier following the merger. The parties are not obligated to complete the merger should any required regulatory approval, waiver or non-objection contain a condition or requirement not normally imposed in such transactions that would deprive Glacier of the economic or business benefits of the merger in a manner that is material relative to the aggregate economic business benefits of the merger to Glacier, subject to certain rights granted in the merger agreement to appeal any denial of such regulatory approval.

Risks Associated with AB’s Business

AB is, and will continue to be, subject to the risks described in AB’s Annual Report on Form 10-K for the fiscal year ended December 31, 2020, as updated by its Quarterly Report on Form 10-Q for the quarter ended March 31, 2021, and subsequent Current Reports on Form 8-K, and Quarterly Reports on Form 10-Q, all of which are filed with the SEC and incorporated by reference into this proxy statement/prospectus. See “References to Additional Information” and “Where You Can Find More Information” included elsewhere in this proxy statement/prospectus.

Risks Associated with Glacier’s Business

Glacier is, and will continue to be, subject to the risks described in Glacier’s Annual Report on Form10-K for the fiscal year ended December 31, 2018,2020, as updated by its Quarterly Report on Form 10-Q for the quarter ended March 31, 2021, and subsequent Current Reports on Form8-K, and Quarterly Reports on Form 10-Q, all of which are filed with the SEC and incorporated by reference into this proxy statement/prospectus. See “References to Additional Information” and “Where You Can Find More Information” included elsewhere in this proxy statement/prospectus.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This document, including information included or incorporated by reference in this document may contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include, but are not limited to,to: (i) statements about the benefits of the merger, including future financial and operating results, cost savings, enhancements to revenue and accretion to reported earnings that may be realized from the merger;(ii) statements about our respectiveGlacier’s and AB’s plans, objectives, expectations, intentions, projected financial information, future opportunities and intentions andany other statements regarding Glacier’s and AB’s future expectations, beliefs, plans, objectives, results of operations, financial condition and cash flows that are not historical facts; (iii) the expected timetable for completing the merger; (iv) the ability to complete the merger; and(iii) (v) other statements identified by words such as “expects,” “anticipates,” “intends,” “plans,” “believes,” “seeks,” “estimates,” or words of similar meaning. These forward-looking statements are based on current beliefs and expectations of Glacier’s and AB’s management and are inherently subject to significant business, economic and competitive uncertainties and contingencies, many of which are beyond Glacier’s and FNB’sAB’s control. In addition, these forward-looking statements are subject to assumptions with respect to future business strategies and decisions that are subject to change.

In addition to factors previously disclosed in Glacier’s and AB’s reports filed with the SEC relating to risks to Glacier’s and AB’s business and stock price, and those identified elsewhere in this document (including the section entitled “Risk Factors”), the following potential factors, among others, could cause actual results to differ materially from the anticipated results or other expectations expressed or implied in the forward-looking statements:

The foregoing list of factors is not intended to be exhaustive. These forward-looking statements reflect Glacier’s and AB’s current views with respect to future events and are based on numerous assumptions and assessments made by Glacier and AB in light of their experiences and perceptions of historical trends, current conditions, business strategies, operating environments, future developments and other factors they believe appropriate. By their nature, forward-looking statements involve known and unknown risks and uncertainties because they relate to events and depend on circumstances that will occur in the future. The factors described in the context of such forward-looking statements in this document could cause Glacier’s and AB’s plans with respect to the merger, actual results, performance or achievements, industry results and developments to differ materially from those expressed in or implied by such forward-looking statements. Although it is believed that the expectations reflected in such forward-looking statements are reasonable, no assurance can be given that such expectations will prove to have been correct and persons reading this document are therefore cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date of this proxy statement/prospectus or, in the case of a document incorporated by reference, as of the date of that document. All subsequent written and oral forward-looking statements concerning the proposed transaction or other matters attributable to Glacier or FNBAB or any person acting on behalf of Glacier or FNBAB are expressly qualified in their entirety by the cautionary statements above. Neither Glacier nor FNBAB undertakes any obligation to update any forward-looking statements to reflect circumstances or events that occur after the date the forward-looking statements are made.

SELECTED HISTORICAL FINANCIAL INFORMATION OF GLACIER

The following table presents selected consolidated financial information of Glacier for the fiscal years ended December 31, 2018, 2017, 2016, 2015, and 2014. The consolidated financial data below should be read in conjunction with the consolidated financial statements and notes thereto, incorporated by reference in this proxy statement/prospectus. See “Where You Can Find More Information.”

FNBAB SPECIAL SHAREHOLDERS’ MEETING

Date, Time, Place

The FNBAB special meeting of shareholders will be held on April 18, 2019,[___], 2021, at 10:[___] Mountain Time. The special meeting will be held in virtual meeting format only. In order to attend the special meeting, AB shareholders must register at www.proxydocs.com/ALTA by 5:00 a.m.p.m. Mountain Time at the Davis Conference Center located at 1651 North 700 West, Layton, Utah 84041.on [__], 2021.

As described below under the “Votes Required and Quorum,” approval of the merger agreement requires the affirmative vote of at least a majority of the outstanding shares of FNB’s outstandingAB’s common stock.stock entitled to vote on the matter. The proposal to approve merger-related compensation to named executives on an advisory basis will be approved if the votes cast in favor of the proposal exceed the votes cast opposing the proposal, assuming a quorum is present. The proposal to adjourn the special meeting, if necessary or appropriate, including adjournments to solicit additional proxies, will be approved if the votes cast in favor of the proposal exceed the votes cast againstopposing the proposal, assumingwhether or not a quorum is present. If less than a quorum is represented at the special meeting, a majority of the shares so represented may adjourn the special meeting without further notice.

Purpose

At the special meeting, FNBAB shareholders will:

Record Date; Shares Outstanding and Entitled to Vote

The FNBAB Board has fixed 5:00 p.m. Mountain Timethe close of business on March 6, 2019[___], 2021, as the record date for determining the holders of shares of FNBAB common stockshares entitled to notice of and to vote at the special meeting. At the close of business on the record date, there were approximately 147[___] holders of record and 3,160,969[___] AB common shares of FNB common stock issued and outstanding. Holders of record of FNBAB common stockshares on the record date are entitled to one vote per share and are also entitled to exercise dissenters’ rights if certain procedures are followed. See “The Merger – Dissenters’ Rights” andAppendix B.share. Unvested RSUs do not have voting rights.

FNB’sAB’s directors and executive officers and certain significant shareholders have agreed to vote all shares of FNBAB common stockshares they are entitled to vote that are held or controlled by them in favor of approval of the merger agreement. As of the record date, hereof, a total of 1,357,605[_________] AB common shares, of FNB common stock, representing approximately 42.95%[____]% of all outstanding AB common shares of FNB common stock, are covered by thesubject to voting agreement.agreements. See “The Merger – Interests of FNB Directors and Executive Officers in the Merger – Voting Agreement.”Agreements”.

Votes Required and Quorum

The affirmative vote of the holders of at least a majority of the outstanding shares of FNB’s outstandingAB’s common stock entitled to vote is required to approve the merger agreement. At least a majority of the total outstanding AB common shares of FNB common stockentitled to vote must be present, either in personat the meeting or by proxy, in order to constitute a quorum for the special meeting. For purposes of determining a quorum, abstentions areand broker non-votes will be counted in determining the shares present at a meeting.

With respect to the merger-related named executive compensation proposal, approval of such proposal requires that the votes cast in favor of the proposal exceed the votes cast opposing the proposal. As a result, abstentions and broker non-votes with respect to the merger-related named executive officer compensation proposal will have no effect on the merger-related named executive officer compensation proposal.

With respect to the proposal to adjourn the special meeting if necessary or appropriate, if a quorum is representednot present at the special meeting, a majority ofshareholders entitled to vote at the shares so represented mayspecial meeting, present at the meeting or by proxy, will have the power to adjourn the special meeting. If a quorum is present at the special meeting, without further notice. Thethe proposal to adjourn the special meeting, if necessary or appropriate, including adjournmentsan adjournment to solicit additional proxies in favor of the merger agreement, will be approved if the votes cast in favor of the proposal exceed the votes cast againstopposing the proposal, assuming a quorum is present.proposal.

Voting, Solicitation, and Revocation of Proxies

If you are a holder of record of AB common shares as of the record date for the special meeting, there are four ways to have your shares voted:

If the enclosed proxy card is duly executed and received in time for the special meeting, it will be voted in accordance with the instructions given. If the proxy card is duly executed and received but no instructions are given, it is the intention of the persons named in the proxy to vote the shares represented by the proxyFOR the approval of the merger agreement, FOR the proposal to approve merger-related compensation of AB’s named executive officers andFOR the proposal to approve one or more adjournments to solicit additional proxies, and in the proxy holder’s discretion on any other matter properly coming before the meeting. Any proxy given by a shareholder may be revoked before its exercise by:

FNBAB is soliciting the proxy for the special meeting on behalf of the FNBAB Board. FNBAB will bear the cost of solicitation of proxies from its shareholders. In addition to using the mail, FNBAB may solicit proxies by personal interview, telephone, and facsimile. Banks, brokerage houses, other institutions, nominees, and fiduciaries will be requested to forward their proxy soliciting material to their principals and obtain authorization for the execution of proxies. FNB does not expect to pay any compensation for the solicitation of proxies. However, FNBAB will, upon request, pay the standard charges and expenses of banks, brokerage houses, other institutions, nominees, and fiduciaries for forwarding proxy materials to and obtaining proxies from their principals.

Voting in Person at the Special Meeting

Shares helddirectly in your name as the shareholder of record may be voted in person atduring the special meeting. If you choose to vote your shares of FNB common stock in person, please bringmeeting by following the enclosed proxy card or proof of identification.instructions available on the meeting website. Even if you plan to attendparticipate at the virtual special

meeting, we recommendAB recommends that you vote your shares of FNBAB common stockshares in advance as described above so that your vote will be counted if you later decide not to attend the special meeting.

If your shares are registered in “street name” in the name of a broker or other nominee and you wish to vote during the special meeting, you will need to obtain a legal proxy from your bank or brokerage firm. Please consult the voting form sent to you by your bank or broker to determine how to obtain a legal proxy in order to vote at the meeting.

The AB Proposals

Proposal 1: Merger Proposal

AB is asking its shareholders to approve the merger agreement. For a detailed discussion of the terms and conditions of the merger agreement, please see the section entitled “The Merger.” AB shareholders should read this proxy statement/prospectus, including any documents incorporated in this proxy statement/prospectus by reference, and its annexes, carefully and in their entirety for more detailed information concerning the merger agreement and the merger. A copy of the merger agreement is attached to this proxy statement/prospectus as Appendix A.

As discussed in the section entitled “Background of and Reasons for the Merger,” after careful consideration, the AB Board approved the execution, delivery and performance of the merger agreement and the transactions contemplated by it, including the merger, and determined the merger to be fair and in the best interests of AB and the AB shareholders.

Required Vote

Approval of the proposal to approve the merger agreement requires the affirmative vote of at least a majority of the outstanding shares of AB’s common stock entitled to vote. If you mark “ABSTAIN” on your proxy card, fail to submit a proxy card or fail to vote by mail, by telephone, via the Internet, or via remote participation through the virtual format of the meeting at the AB special meeting, or are a “street name” holder and fail to instruct your bank, broker, or other nominee how to vote, it will have the same effect as votes against the merger proposal.

The approval of the merger by holders of AB common shares is a condition to the completion of the merger.

The AB Board recommends that AB shareholders vote “FOR” the proposal to approve the merger agreement.

Proposal 2: Advisory Proposal to Approve Merger-Related Named Executive Officer Compensation

Pursuant to Section 14A of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), AB is providing its shareholders with the opportunity to cast an advisory (non-binding) vote to approve the compensation that may be paid or become payable to its named executive officers that is based on or otherwise relates to the merger, as disclosed in the section entitled “The Merger—Interests of AB Directors and Executive Officers in the Merger.” As required by Section 14A of the Exchange Act, AB is asking its shareholders to vote to adopt the following resolution:

“RESOLVED, that the compensation that may be paid or become payable to AB’s named executive officers that is based on or otherwise relates to the merger, and the agreements or understandings pursuant to which such compensation may be paid or become payable, in each case as disclosed pursuant to Item 402(t) of Regulation S-K in the section of the proxy statement/prospectus statement entitled “The Merger—Merger-Related Compensation for AB’s Named Executive Officers”, are hereby APPROVED.”

Required Vote

Approval of the advisory proposal to approve merger-related named executive officer compensation requires that the number of votes cast in favor of the proposal exceed the votes cast opposing the proposal,

assuming a quorum is present. If you mark “ABSTAIN” on your proxy card, fail to submit a proxy card or fail to vote by mail, by telephone, via the Internet, or via remote participation through the virtual format of the meeting at the AB special meeting, or are a “street name” holder and fail to instruct your bank, broker, or other nominee how to vote, it will have no effect on the merger-related named executive officer compensation proposal.

The vote to approve the merger-related named executive officer compensation proposal is a vote separate and apart from the vote to approve the merger agreement. Accordingly, a shareholder may vote to approve the merger-related named executive officer compensation proposal and vote not to approve the merger agreement or vice versa. Because the merger-related named executive officer compensation proposal vote is advisory only, it will not be binding on the parties to the merger. If the merger is completed, the merger-related named executive officer compensation subject to the merger-related named executive officer compensation proposal will be paid to AB’s named executive officers to the extent payable in accordance with the terms of the applicable compensation agreements and arrangements even if holders of AB common shares fail to approve the merger-related named executive officer compensation proposal.

The approval of the merger-related named executive officer compensation proposal is not a condition to the completion of the merger.

The AB Board recommends a vote “FOR” the proposal to approve merger-related compensation of AB’s named executive officers.

Proposal 3: Adjournment Proposal

AB is asking its shareholders to approve the adjournment of the AB special meeting to another date and place if necessary or appropriate to solicit additional votes in favor of the merger proposal if there are insufficient votes at the time of such adjournment to approve the merger proposal.

If, at the AB special meeting, an insufficient number of AB common shares are present via remote participation through the virtual format of the meeting or represented by proxy and voting in favor of the merger proposal, AB will move to adjourn the AB special meeting to enable the AB Board to solicit additional proxies for approval of the merger proposal. If the AB shareholders approve the adjournment proposal, AB may adjourn the AB special meeting and use the additional time to solicit additional proxies, including the solicitation of proxies from AB shareholders who have previously voted. If the date of the adjournment is not announced at the AB special meeting or a new record date is fixed for the adjourned meeting, a new notice of the adjourned meeting will be given to each shareholder of record entitled to vote at the adjourned meeting.

Required Vote

Approval of the adjournment proposal requires that the number of votes cast in favor of the proposal exceed the votes cast opposing the proposal, whether or not a quorum is present. If you mark “ABSTAIN” on your proxy card, fail to submit a proxy card or fail to vote by mail, by telephone, via the Internet, or via remote participation through the virtual format of the meeting at the AB special meeting, or are a “street name” holder and fail to instruct your bank, broker, or other nominee how to vote, it will have no effect on the adjournment proposal.

The AB Board recommends that AB shareholders vote “FOR” the adjournment proposal.

Other Matters to Come Before the AB Special Meeting

As of the date of this proxy statement/prospectus, the AB Board is not aware of any matters that will be presented for consideration at the AB special meeting other than as described in this proxy statement/prospectus. If, however, the AB Board properly brings any other matters before the AB special meeting, the persons named in the proxy will vote the shares represented thereby in accordance with the recommendation of the AB Board on any such matter.

BACKGROUND OF AND REASONS FOR THE MERGER

Background of the Merger

FromThe AB Board, with the assistance of executive management, periodically reviews, assesses, and discusses AB’s strategic direction, performance, and prospects. These reviews and discussions have included from time to time, third party advisors, including investment bankers and external legal counsel, and have addressed the FNBpotential strategic alternatives that might be available to AB, including organic growth opportunities, potential mergers and acquisitions (including potential acquisition targets and the sale of AB), and capital planning decisions, all with the goal of enhancing shareholder value. These reviews and discussions have also included analyses of the business environment for financial institutions, including technology initiatives and investments, the impact of low interest rates, the evolution of community banking, and talent acquisition and retention. Economic outlook nationally and locally, the regulatory and compliance environment, financial institution industry trends, peer comparisons, ongoing consolidation among financial institutions, and the benefits and risks of continued operation as a standalone company have also been considered. Factors assessed in connection with these reviews have included the risks and opportunities associated with operating in existing and new markets, competition, potential positive and negative expense and revenue synergies, regulatory requirements, interest rate environment and prospects, scale, operational risk, credit risk, market risk, and changes in technology and in delivery and marketing channels. In connection with the evaluation of strategic alternatives, AB’s executive management has had, from time to time, informal discussions, including regarding potential acquisitions or the sale of AB, with representatives of other financial institutions and has regularly updated the AB Board has discussed, analyzedregarding such discussions.

Randall M. Chesler, President and considered the valueChief Executive Officer of Glacier, and significanceLen E. Williams, President and Chief Executive Officer of FNB to its shareholders, customers, and employees, as well as the vital role it has playedAB, have lengthy careers in the local communityfinancial institutions industry and have known each other professionally for over 110 years. In recentthe last two to three years several bank holding companiessince Mr. Williams joined AB. Messrs. Chesler and Williams have expressedperiodically informally discussed matters of mutual interest in pursuingto their respective institutions, and Mr. Chesler inquired on at least one occasion about a combinationpotential business combination.

Certain members of the Gunther family and their related entities (the “Section 13D Group”) executed a shareholder agreement on January 28, 2020 and jointly filed a Schedule 13D with FNB, including a mergerthe Securities & Exchange Commission on June 12, 2020. At the time, two of equals and an acquisition by a larger institution. Asthe 10 members of the AB Board were part of its responsibility to consider these expressionsthe Section 13D Group.

To avoid potential conflicts of interest the FNB Board engaged Sandler O’Neill in April of 2014and to provide strategic advisory services to FNB. The FNB Board considered each of the opportunities as they arose, and each time the FNB Board ultimately determined that remaining independent was inadvance the best interests of the shareholders they represented.

Like many other community banks, the FNB Board has strategized around a number of business issues including: increasing competition from bank andnon-bank institutions, continued allowance of regulatory overreach from local credit unions, heightened compliance and regulatory risk, succession planning around an aging management team, and maintaining loan growth in the face of rising real estate lending concentrations. At an FNB Board meeting in May of 2018, President and Chief Executive Officer K. John Jones presented a shareholder value analysis. The FNB Board considered the analysiscompany and its dutyshareholders, in July of 2020, all 10 members of the AB Board unanimously voted to maximize value for shareholders, as well its responsibility for maintainingestablish a special committee comprising all directors other than the historic legacydirectors that were members of servicethe Section 13D Group to act on behalf of the company with respect to considering and responding to the local community, dedicated employees,goals and requests of the Section 13D Group.

In August 2020, the AB Board convened its regularly scheduled annual two-day retreat to review, assess, and set the company’s strategic direction. As is customary practice, the AB Board, with the assistance of executive management, considered and set various key strategic objectives for the company. In addition, the AB Board and executive management considered and discussed the contents and potential impacts of the Schedule 13D filing by the Section 13D Group. After considering the positive performance trajectory of the company, the successful implementation of technology initiatives, and the loyal customer base. The FNBexperience and capabilities of executive management, among other factors, the AB Board concluded that remaining independent was inadopted and endorsed the best interests ofstrategic direction for the shareholders but confirmed that that if FNB received a bona fide acquisition proposal that would reasonably be expected to result in a certain value for shareholders, that the FNB Board would need to seriously consider the proposal as an alternative to remaining independent, consistent with its fiduciary duty to the shareholders.

Following the FNB Board’s decisioncompany, including to remain independent Mr. Jones contacted representativesand pursue organic growth and potential acquisition opportunities.

In November 2020, executive management presented an opportunity to acquire a bank outside of Sandler O’Neill in early Julythe state of 2018Utah. The AB Board unanimously directed executive management to begin formal discussions with Party X regarding a potential acquisition.

During the course of the next several months, at regularly-scheduled Board meetings and terminatedthrough periodic communications with the existing engagement letter.AB Board, executive management provided the AB Board updates on unsolicited

contacts and inquiries from third parties regarding a possible sale of 2018 the Chief Executive Officercompany, including unsolicited approaches from Glacier and Party B, key metrics on the company’s strategic direction adopted at the AB Board’s annual retreat, and progress on various potential acquisition opportunities.

On January 11, 2021, the AB Board unanimously approved the submission of a non-binding letter of interest to Party X regarding the acquisition of Party X by AB.

On January 15, 2021, Paul Gunther, a member of the Section 13D Group, resigned as a director of AB.

At a special meeting convened on January 15, 2021, the AB Board considered and discussed the strategic objectives of the company. Mr. Williams also provided an update to the AB Board on potential acquisition opportunities. In addition, the AB Board considered and discussed the amended Schedule 13D filed by the Section 13D Group on January 14, 2021, which included a letter to the AB Board requesting that the AB Board review strategic alternatives for AB, including a potential sale of the company. The filing also noted the 13D Group’s objection to AB acquiring another bank holding company, which we referand its concern that the current Board of Directors and executive management would be incapable of successfully executing such a transaction. Keefe, Bruyette & Woods, Inc., acting as financial advisor to as Company A, met with FNB’s Chairman, Kevin Garn,AB (“KBW”), was invited to the meeting to discuss businesswith the AB Board the potential process for undertaking a review of the company’s strategic alternatives and how KBW could assist in that review.

At its regularly-scheduled meeting on January 26, 2021, the AB Board received a presentation from Jones Day, legal counsel to AB, regarding the directors’ fiduciary duties under applicable law and related obligations in reviewing and considering strategic alternatives, which was followed by review and discussion with KBW of strategic considerations and the following alternatives: (i) remain standalone/independent; (ii) pursue mergers and acquisitions; (iii) explore a merger of equals; or (iv) undertake a controlled sale process. The market landscape, potential targets, prospective buyers, valuation considerations, and related financial considerations were reviewed and discussed. The AB Board met in executive session to discuss the foregoing, after which the AB Board voted unanimously to continue with the strategic direction previously agreed to in August 2020 at the AB Board’s annual retreat, mainly to remain as an independent entity and pursue potential acquisition opportunities, between Company Aincluding the potential acquisition of Party X.

On January 27, 2021, the Section 13D Group filed an amended Schedule 13D, which included a letter to the AB Board, reiterating the Section 13D Group’s request that AB review strategic alternatives, including a potential sale of the company.

On February 1, 2021, Jonathan Gunther, a member of the Section 13D Group, resigned as a director of AB.

At a special meeting convened on February 11, 2021, The AB Board considered recent developments, including the ongoing consolidation among financial institutions, executive management’s ongoing discussions regarding a potential acquisition opportunity, and FNB. At the meeting, Company A’s Chief Executive Officer expressed his strong interest in acquiring FNB and expressed Company A’s willingnesssignificant potential costs likely to pay a significant merger premium. Following the meeting, Chairman Garn and Mr. Jones discussed the meeting with representatives of Sandler O’Neill and determined it was likely that Company A would make an acquisition proposal that would meet or exceed the threshold establishedbe incurred by the FNB Board at its May 2018 meeting. Accordingly, Chairman Garn and Mr. Jones directed representatives of Sandler O’Neill to contact Company A to try to determine the maximum value that Company A would be willing to offer FNB in an acquisition proposal. As part of this discussion, Chairman Garn, Mr. Jones and representatives of Sandler O’Neill also discussed Glacier and two other potential acquirorsAB and the potential values that they might be willingdisruption to offer FNBAB’s business in an acquisition. Following this conversation, representativesthe event of Sandler O’Neill were instructeda proxy contest. The AB Board discussed the company’s strategic alternatives in light of these developments and how best to contact Glacier and two other bank holding companies, which we referfurther validate the best future strategy for AB. The AB Board determined to as Company B and Company C,direct KBW to gauge their(i) approach prospective buyers to solicit interest in a possible sale of the company and also (ii) to concurrently continue to move forward with a potential acquisition of FNB.Party X.

Throughout August,At the direction of the AB Board, on February 16, 2021 executive management, with the assistance of KBW, commenced the solicitation process for a possible sale of AB. Continuing over the course of several days, representatives of Sandler O’Neill held conversationsKBW contacted or were contacted by potential counterparties, including Glacier. With KBW’s assistance, the AB Board and executive management identified potential buyers of AB with Glacier, Company A(i) the greatest financial ability to pay (based on their relative buying power versus third parties, as determined based on publicly available information) and Company B about(ii) a similar strategic direction and culture as AB. Each of the nine potential

counterparties received initial marketing information and draft non-disclosure agreements. Ultimately, seven of those parties expressed interest in the potential acquisition of FNB. Company C had previously expressedAB, executed customary non-disclosure agreements, received preliminary due diligence information, and received a process letter requesting indications of interest in acquiring FNB but had now determinedby March 12, 2021. Of the parties that it was notexecuted a non-disclosure agreement, four parties elected to receive a management presentation and meeting.

At its regularly-scheduled meeting on February 24, 2021, the AB Board received an update from KBW regarding the sale process, including preliminary due diligence performed by interested in pursuingcounterparties, and the anticipated timeline for indications of interest, as well as an update from executive management on the company’s concurrent pursuit of a potential acquisition discussions with FNB at that time. The conversationsof Party X.

During the period from March 2, 2021 to March 5, 2021, AB conducted management presentations and meetings with Glacier, CompanyParty A, Party B, and Company B included the sharing of publicly available information along with some high-level guidance on acquisition assumptions. In additionParty C.

On March 8, 2021, Glacier’s executive management team and D.A. Davidson & Co., financial advisor to the conversations with representatives of Sandler O’Neill, each of the companiesGlacier (“D.A. Davidson”), met with Chairman Garnthe Glacier board of directors to discuss the pro forma financial modeling and Mr. Jones. In these meetings, Chairman Garn and Mr. Jones emphasized that FNB

FNB’s operations as partAlso on March 15, 2021, the Section 13D Group filed an amended Schedule 13D, which included a letter to AB’s shareholders, announcing the Section 13D group’s intention to consider a “vote no” campaign against certain of AB’s directors.

KBW informed Glacier of the AB Board’s decision to pursue and negotiate a separate divisionbusiness combination transaction with a local advisory board would best serve its customers, employeesGlacier on March 16, 2021. Executive management representatives of Glacier and community,AB negotiated and would likely provide a higher value to shareholdersdiscussed additional deal terms within the parameters discussed with the AB Board over the long-term, than remaining independent. Accordingly,course of the FNBnext several business days, including, without limitation, the amount of Glacier’s requested termination fee and the duration of the exclusivity period to be granted to Glacier for purposes of negotiating a definitive agreement. On March 18, 2021, the parties executed a letter of intent.

Commencing March 22, 2021 and continuing through May 18, 2021, Messrs. Chesler and Williams and other executive management representatives from Glacier and AB, respectively, had periodic telephonic meetings to discuss and negotiate the terms of the merger and potential integration. During this period, Glacier performed extensive diligence of AB, and AB, in turn, undertook reverse diligence of Glacier during this time period. During the diligence process, various working groups from Glacier and AB, including information technology, accounting, retail operations, legal and compliance, credit, human resources, marketing, internal audit, data warehouse, and commercial banking, met virtually to exchange information and discuss the proposed transaction. Representatives of KBW and D.A. Davidson also attended many of these meetings.

At the regularly-scheduled AB Board decidedmeeting on March 31, 2021, Mr. Williams provided the AB Board an update regarding the proposed merger transaction, including the status of due diligence and various potential integration matters. The potential negative impact of the recent decline in Glacier’s stock price, as well as the interest rate effect on the fair valuation of investment securities available for sale and the corresponding recording of the unrealized gain or loss to shareholders’ equity, on the transaction’s economics were discussed. A special meeting of the AB Board was convened on April 1, 2021 to discuss the transaction’s economics further. After consultation with and input from executive management, Jones Day, and KBW, the AB Board directed executive management of the company to move forward with the proposal from Glacier, subject to satisfactory resolution of a few terms of the letter of intent.

Between October 28 and October 30, 2018, FNB and Glacier, with assistance of their respective legal counsel and financial advisors, negotiated several aspects of Glacier’s letter of intent. After several discussions and consideration, Glacier and FNB signed a nonbinding letter of intent on October 30, 2018 which described the principal merger terms and provided that FNB would negotiate with Glacier exclusively for a period of 90 days. Accordingly, FNB’s discussions with Company A and Company B ceased.

Between October 30, 2018 and January 15, 2019, Glacier, FNB and their respective legal counsel and financial advisors conducted appropriate due diligence and draftedKBW and negotiatedexecutive management of the company to continue to monitor closely the transaction economics.

On April 16, 2021, Miller Nash LLP, legal counsel to Glacier (“Miller Nash”), provided an initial draft of the merger agreement. Between that receipt date and May 14, 2021, Miller Nash and Jones Day exchanged drafts of the merger agreement and related ancillary agreements. FNB provided Glacier with information regarding, among other things,transaction documents, including voting agreements to be entered into by each of the financial aspects of its business, its markets and its operations. Glacier provided FNB with information regarding, among other things, its employee benefit policies, its insurance policies and itsnon-competition arrangements with its directors and each of the executive officers.officers of AB and certain other shareholders of AB and non-compete/non-solicitation agreements to be entered into by each of the directors. The two law firms and the respective management teams negotiated, exchanged drafts, and worked towards finalizing the terms and conditions of the merger agreement, the voting agreements and other transaction documents. AB negotiated with Glacier to obtain more favorable terms and conditions in the merger agreement. Reciprocal due diligence continued during this time period as well.

At the April 28, 2021 regularly-scheduled AB Board meeting, Mr. Williams provided the AB Board a detailed update regarding the proposed merger transaction, including the status of due diligence, negotiation of the merger agreement, and various operational and integration matters. With participation from Jones Day, the AB Board reviewed and discussed the negotiation of key terms of the draft merger agreement, proposed voting agreements for executive officers and directors, and proposed non-compete/non-solicitation agreements for directors. The AB Board considered the governance structure of Glacier, including its board of directors as well as its divisional board structure. The AB Board discussed a proposed timeline for completing negotiation and anticipated next steps and directed KBW to meet with D.A. Davidson and Glacier regarding the transaction and the impact of the recent decline in Glacier’s stock price, as well as the interest rate effect on the fair valuation of investment securities available for sale and the corresponding recording of the unrealized gain or loss to shareholders’ equity.

On May 10, 2021, a special meeting of the AB Board was convened. KBW updated the AB Board on its discussion with Glacier and D.A. Davidson about the transaction’s economics. Jones Day addressed the status of the legal documentation for the proposed transaction. The proposed timing and strategy for approaching the Section 13D Group regarding the proposed transaction was also discussed. The Board discussed the overall strength and viability of the proposed transaction, taking into account the fluctuation in the implied valuation as a result of changes in stock prices, and the AB Board instructed executive management of AB to continue to move forward negotiating the potential transaction with the assistance of AB’s external advisors. The AB Board also authorized executive management and the advisors of AB to contact Davis Partnership, L.P., Davis Capital Partners, LLC and Lansing Davis (collectively, the “Davis Group”) and representatives for the Section 13D Group in connection with the potential transaction.

Also on May 10, 2021, Mr. Williams approached the Davis Group regarding execution of a customary non-disclosure agreement to facilitate discussion about the potential transaction and garnering the group’s support for the same through execution of a voting agreement.

On September 6May 11, 2021, the Davis Group entered into a non-disclosure agreement.

On or about May 11, 2021, as directed by the AB Board, KBW and 7, 2018, representativesJones Day approached the investment banker and legal counsel, respectively, for the Section 13D Group regarding execution of a customary non-disclosure agreement to facilitate discussion about the potential transaction and garnering the group’s support for the same through execution of a voting agreement.

On May 12, 2021, the Section 13D Group entered into a non-disclosure agreement with AB, after which KBW and Jones Day discussed with the Section 13D Group’s advisors the general terms of the proposed transaction and the request for execution of a voting agreement. During the period from May 12, 2021 to May 17, 2021, legal counsel to the Section 13D Group, Miller Nash, Jones Day, and executive management of AB negotiated and exchanged drafts of the voting agreement.

Also on May 12, 2021, Mr. Williams discussed the potential transaction and the voting agreement with the Davis Group. During the period between May 12, 2021 and May 17, 2021, legal counsel to the Davis Group, Miller Nash, Jones Day and management of AB negotiated and exchanged drafts of the voting agreement.

Also on May 12, 2021, certain executive officers of AB were presented with draft employment agreements to be entered into in connection with the signing of the merger agreement. During the period from May 12, 2021 to May 16, 2021, Miller Nash and certain executive officers of AB and their independent counsel negotiated and exchanged drafts of the employment agreements.

On May 17, 2021, at the Section 13D Group’s request, Mr. Chesler, Craig A. Langel, chair of Glacier’s Board of Directors, Ronald J. Copher, Executive Vice President and Chief Financial Officer of Glacier, were accompanied by representativesand Donald J. Chery, Executive Vice President and Chief Administrative Officer of FNB on a due diligence trip to review the branches of FNB and its markets. Glacier, representatives met with representatives from FNBof the Section 13D Group to discuss the transactionproposed transaction.

Also on May 17, 2021, a special meeting of the AB Board was convened to consider the proposed merger transaction. Members of executive management and conduct due diligence interviews.

On January 4, 2019, representatives of Glacier informed representativesKBW and Jones Day attended the meeting at the invitation of FNB that Glacier’s due diligence revealed higher transaction expensesthe AB Board. The AB Board was provided with a set of meeting materials in advance of the meeting, including substantially final drafts of the merger agreement, the voting agreements which included key members of the Section 13D Group and the Davis Group, the non-competition/non-solicitation agreements, and a higher reserve for loan losses than initially anticipated. As a result, Glacier offered a reduced exchange ratiosummary of 0.6474 Glacier shares in exchange for each FNB share.

On January 9, 2019, representatives from FNB, Sandler O’Neill and Glacier participated in a reverse due diligence conference call to provide information to FNB regarding Glacier and answer questions from FNB and Sandler O’Neill.

On January 10, 2019, the FNB Board, together with representativesmaterial terms of Sandler O’Neill and legal counsel, met to consider Glacier’s due diligence findings, the reduced exchange ratio and the proposed definitive merger agreement as negotiatedprepared by Jones Day. Jones Day discussed with the directors their fiduciary duties under applicable law and reviewed the accompanying legal standards. Jones Day proceeded to date. Representativesreview in detail with the AB Board the terms of Sandler O’Neillthe merger agreement, including the terms of various ancillary documents. KBW then reviewed the financial aspects of the proposed merger. FNB’s legal counsel reviewedtransaction, including the specific terms of the merger agreement and the substantial process involved in negotiating its terms. The FNB Board considered all these matters and determined that the reduced offer still constituted s significant premium and unanimously confirmed its desirefinancial analyses with respect to proceed with the proposed merger.

On January 11, 2019, FNB management conducted onsite diligence at Glacier’s headquarters.

On January 15, 2019, the FNB Board, together with representatives of Sandler O’Neilltransaction that KBW performed, and legal counsel, again met to consider the negotiated proposed definitive merger agreement. Representatives of Sandler O’Neill reviewed the financial aspects of the proposed merger andKBW rendered to the FNBAB Board a verbalan opinion, which was subsequentlyinitially rendered verbally and confirmed in writing,a written opinion dated May 17, 2021, to the effect

that, as of thatsuch date and subject to the procedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by Sandler O’Neill,KBW as set forth in its opinion, the merger considerationexchange ratio in the proposed merger with Glacier was fair, from a financial point of view, to the holders of FNBAB common stock. Legal counsel then reviewedshares. The AB Board considered the termsvalues of the proposed merger agreementother acquisition proposals that had been previously received, taking into account changes in stock prices, and noted that the changes toconsideration in the proposed merger agreement sincetransaction with Glacier was still clearly the FNB Board’s January 10 meeting. Among other matters considered,best for shareholders.

After considering the FNB Board reviewed

In the course of reaching this determination and relatedits decision to approve the merger agreement, the FNB Board evaluated the merger and the merger agreement in consultation with the management of FNB and FNB’s financial advisor and legal counsel. In reaching its determination, the FNB Board considered a number of factors. Such factors also constituted the reasons that the FNB Board determined to approveother transactions contemplated by the merger agreement and to recommend that FNBthe AB shareholders vote in favor of“FOR” the proposal to approve the merger agreement. Such reasons includedagreement, the following:AB Board evaluated the merger agreement, the merger, and the other transactions contemplated by the merger agreement in consultation with AB’s executive management, as well as AB’s financial advisor, KBW, and legal advisor, Jones Day, and considered various factors, including, without limitation, the following material factors:

The foregoing discussion of the reasons that ledinformation and factors considered by the FNBAB Board to approve the merger agreement and recommend that FNB’s shareholders vote in favor of the merger agreement is not intended to be exhaustive, but, is believedrather, includes the material factors considered by the AB Board. In reaching its decision to include allapprove the merger agreement, the merger of the material reasons forBank into Glacier Bank and the FNB Board’s decision. In reachingother transactions contemplated by the merger agreement, the AB Board did not quantify or assign any relative weights to the factors considered, and individual directors may have given different weights to different factors. The AB Board considered all these factors as a whole and overall considered the factors to be favorable to, and support, its determination to approve and recommend the transaction, the FNB Board based its recommendation on the totalitymerger agreement.

It should be noted that this explanation of the AB Board’s reasoning and all other information presented to itin this section is forward-looking in nature and, did not assign any relative or specific weights totherefore, should be read in light of the reasons considered in reaching that determination. Individual directors may have given differing weights to different reasons. After deliberating with respect tofactors discussed under the merger with Glacier, considering, among other things, the matters discussed above, the FNB Board unanimously approved the merger agreement and the merger with Glacier as being in the best interests of FNB and its shareholders.heading “Cautionary Statement Regarding Forward-Looking Statements.”

Opinion of FNB’sAB’s Financial Advisor

FNB retained Sandler O’NeillAB engaged KBW to actrender financial advisory and investment banking services to AB, including an opinion to the AB Board as an independentto the fairness, from a financial advisorpoint of view, to FNB’s boardthe common shareholders of directorsAB of the exchange ratio (referred to elsewhere in connection with FNB’s consideration of a possible business combination. Sandler O’Neillthis proxy statement/prospectus as the per share stock consideration) in the proposed merger. AB selected KBW because KBW is a nationally recognized investment banking firm whose principal business specialty is financial institutions. Inwith substantial experience in transactions similar to the ordinary coursemerger. As part of its investment banking business, Sandler O’NeillKBW is regularlycontinually engaged in the valuation of financial institutionsservices businesses and their securities in connection with mergers and acquisitions and other corporate transactions.acquisitions.

Sandler O’Neill acted as an independent financial advisor in connection withAs part of its engagement, representatives of KBW attended the meeting of the AB Board held on May 17, 2021, at which the AB Board evaluated the proposed transaction and participated in certaintransaction. At this meeting, KBW reviewed the financial aspects of the negotiations leadingproposed merger and rendered to the execution of the merger agreement. At the January 15, 2019 meeting at which FNB’s board of directors considered and discussed the terms of the merger agreement and the merger, Sandler O’Neill delivered to FNB’s board of directors its oralAB Board an opinion which was subsequently confirmed in writing, to the effect that, as of January 15, 2019, the merger consideration provided for in the merger agreement was fairsuch date and subject to the holders of FNB common stock from a financial point of view. The full text of Sandler O’Neill’s opinion is attached as Appendix C to this proxy statement/prospectus. The opinion outlines the procedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by Sandler O’NeillKBW as set forth in rendering its opinion. opinion, the exchange ratio in the proposed merger was fair, from a financial point of view, to the holders of AB common shares. The AB Board directors approved the merger agreement at this meeting.

The description of the opinion set forth belowherein is qualified in its entirety by reference to the full text of the opinion. Holders of FNB common stock are urgedopinion, which is attached as Appendix B to readthis document and is incorporated herein by reference, and describes the entire opinion carefullyprocedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by KBW in connection with their consideration ofpreparing the proposed merger.