GLACIER BANCORP, INC.

The information set forth below supplements the proxy statement/prospectus and should be read in conjunction with the proxy statement/prospectus, which should be read in its entirety. To the extent that information herein differs from or updates information contained in the proxy statement/prospectus, the information contained herein supersedes the information contained in the proxy statement/prospectus. All page references below are to pages in the proxy statement/prospectus, and terms used below shall have the meanings set forth in the proxy statement/prospectus (unless otherwise defined below).

The second full paragraph on page 31 of the proxy statement/prospectus under the Section “Background and Reasons for the Merger—Background of the Merger” is hereby amended and restated as follows (supplemental disclosure is underlined):

On January 6, 2025, Guaranty entered into a confidentiality agreement, which did not contain any standstill or “don’t ask, don’t waive” provisions, with Company A and Company A was given access to preliminary diligence materials regarding Guaranty.

The eighth full paragraph on page 31 of the proxy statement/prospectus under the Section “Background and Reasons for the Merger—Background of the Merger” is hereby amended and restated as follows (supplemental disclosure is underlined):

On February 10, 2025, Company A delivered to Guaranty a non-binding letter of intent with respect to a potential business combination between Guaranty and Company A (the “Company A LOI”). The Company A LOI described the material financial components of a proposed all-cash transactionof $525 million, inclusive of Guaranty stock options, and included other merger expectations and assumptions.

The tenth full paragraph on page 31 of the proxy statement/prospectus under the Section “Background and Reasons for the Merger—Background of the Merger” is hereby amended and restated as follows (supplemental disclosure is underlined):

On February 24, 2025, Guaranty and Glacier entered into amutual confidentiality agreement, which did not contain any standstill or “don’t ask, don’t waive” provisions, and Glacier was given access to confidential diligence materials regarding Guarantyand Guaranty was given access to confidential information regarding Glacier.

The last paragraph on page 31 of the proxy statement/prospectus under the Section “Background and Reasons for the Merger—Background of the Merger” is hereby amended and restated as follows (supplemental disclosure is underlined):

On March 31, 2025, Guaranty received an initial non-binding indication of interest letter (the “March 31 LOI”) from Glacier that contemplated Glacier acquiring 100 percent of the outstanding Guaranty common shares through the merger of Guaranty with and into Glacier, with Glacier surviving. The March 31 LOI contemplated that upon consummation of the proposed transaction, all of the outstanding Guaranty common shares would be converted into the right to receive Glacier common shares, based on a fixed exchange ratio of 0.9300x. The March 31 LOI also contemplated that, consistent with Glacier’s model, the Bank’s operations would be conducted through a new bank division to be known as, “Guaranty Bank & Trust, Division of Glacier Bank” and that the current management team of the Bank would continue to manage and operate the new division with guidance from a locally-based bank division board, consisting initially of the existing directors on the Bank and Mr. Chesler. Pursuant to the March 31 LOI, Glacier expressed its desire that Mr. Abston would enter into a new employment agreement with Glacier substantially similar to his existing employment agreement with Guaranty but did not include any specific terms. The March 31 LOI provided for an exclusivity period of 90 days and that the March 31 LOI will expire at the close of business on April 8, 2025, if not accepted by Guaranty.

The fifth full paragraph on page 32 of the proxy statement/prospectus under the Section “Background and Reasons for the Merger—Background of the Merger” is hereby amended and restated as follows (supplemental disclosure is underlined):

On April 11, 2025, Guaranty received from Glacier a revised non-binding indication of interest letter (the “April 11 LOI”). The April 11 LOI contemplated that upon consummation of the proposed transaction, all of the outstanding Guaranty common shares would be converted into the right to receive Glacier common shares, based on a fixed exchange ratio of 1.0000x, and a proposed total deal value of approximately $537 million, using assumptions in effect at the time. The April 11 LOI provided that such valuation assumed a Guaranty consolidated tangible common equity of $292 million at March 31, 2025, plus the amount of capital attributable to the exercise of Guaranty options after March 31, 2025, if any, along with various other assumptions on cost savings, transaction-related expenses and purchase accounting marks to be confirmed in due diligence. The April 11 LOI contemplated that any changes in Guaranty’s consolidated tangible common equity (including any changes in the accumulated other comprehensive income and changes in the fair value of the held-to-maturity securities portfolio) between March 31, 2025, and a measurement date prior to closing of the merger would be eligible to be paid out to Guaranty shareholders as an additional cash dividend, or if a negative number, would be recognized as a price adjustment on a dollar-for-dollar basis, reflected as a reduced exchange ratio. The April 11 LOI reiterated the same provisions regarding the Bank operating as a new division with a locally-based board and the expectation that Mr. Abston would enter into a new employment agreement with Glacier. The April 11 LOI provided for an exclusivity period of 90 days and that the April 11 LOI will expire at the close of business on April 18, 2025, if not accepted by Guaranty.

The penultimate full paragraph on page 33 of the proxy statement/prospectus under the Section “Background and Reasons for the Merger—Background of the Merger” is hereby amended and restated as follows (supplemental disclosure is underlined):

On June 9, 2025, Norton Rose received a draft of Mr. Abston’s employment agreement and post-closing payment agreement setting forth the specific terms of each agreement.

The disclosure on page 44 of the proxy statement/prospectus under the section “Opinion of Guaranty’s Financial Advisor – Glacier Selected Companies Analysis” is hereby supplemented by adding the following paragraph below the second table:

The low and high stock price-to-tangible book value per share multiples of the selected companies in the “Glacier Selected Companies Analysis” were 0.86x and 2.00x, respectively, the low and high stock price-to-2025 estimated EPS multiples of the selected companies were 11.2x and 15.1x, respectively, and the low and high stock price-to-2026 estimated EPS multiples of the selected companies were 8.4x and 13.0x, respectively.

The disclosure on page 45 of the proxy statement/prospectus under the section “Opinion of Guaranty’s Financial Advisor – Guaranty Select Companies Analysis” is hereby supplemented by adding the following paragraph below the third table:

The low and high stock price-to-tangible book value per share multiples of the selected companies in the “Guaranty Selected Companies Analysis” were 0.88x and 1.81x, respectively, the low and high stock price-to-2025 estimated EPS multiples of the selected companies were 8.9x and 11.4x, respectively, and the low and high stock price-to-2026 estimated EPS multiples of the selected companies were 8.3x and 10.7x, respectively.

The disclosure on page 46 of the proxy statement/prospectus under the section “Opinion of Guaranty’s Financial Advisor – Selected Transactions Analysis” is hereby supplemented by amending and restating the table of selected transactions as follows:

The disclosure on page 47 of the proxy statement/prospectus under the section “Opinion of Guaranty’s Financial Advisor – Selected Transactions Analysis” is hereby supplemented by adding the following paragraph below the first table:

The low and high price-to-tangible book value per share multiples of the selected transactions in the “Selected Transactions Analysis” were 1.00x and 2.02x, respectively, the low and high pay-to-trade ratios of the selected transactions were 0.63x and 1.29x, respectively, the low and high price-to-LTM EPS multiples of the selected transactions (excluding the impact of the LTM EPS multiple for one of the selected transactions, which was considered not meaningful because it was greater than 30.0x) were 6.5x and 18.8x, respectively, and the low and high core deposit premiums of the selected transactions were 0.0% and 15.6%, respectively. For the 10 selected transactions in which FWD EPS for the acquired company was available at announcement, the low and high price-to-FWD EPS multiples of the selected transactions were 6.1x and 16.1x, respectively. For the 10 selected transactions in which the acquired company was publicly traded, the low and high one-day market premiums of the selected transactions were 3.1% and 80.0%, respectively.

The disclosure on page 48 of the proxy statement/prospectus under the section “Opinion of Guaranty’s Financial Advisor – Financial Impact Analysis” is hereby supplemented by amending and restating the third to last sentence of the first full paragraph as follows (supplemental disclosure is underlined):

This analysis indicated the merger could be accretive to Glacier’s estimated 2026 and 2027 EPSby 7.4% and 7.7%, respectively, and could be dilutive to Glacier’s estimated tangible book value per share at closing assumed as of December 31, 2025 by 0.6%.

The disclosure in the last full paragraph page 48 of the proxy statement/prospectus under the section “Opinion of Guaranty’s Financial Advisor – Guaranty Dividend Discount Model Analysis” is hereby supplemented by adding the following language to the end of the paragraph:

The ranges of discount rates assumed in the “Glacier Dividend Discount Model Analysis,” the “Guaranty Dividend Discount Model Analysis” and the “Illustrative Pro Forma Combined Dividend Discount Model Analysis” of 12.50% to 14.50% in all three analyses were selected by taking into account capital asset pricing model implied cost of capital calculations and other factors based on KBW’s experience and judgment.

The disclosure on page 49 of the proxy statement/prospectus under the section “Opinion of Guaranty’s

Financial Advisor – Miscellaneous” is hereby supplemented by amending and restating the first sentence of the last full paragraph on page 49 as follows (supplemental disclosure is underlined):

Pursuant to the KBW engagement agreement, Guaranty agreed to pay KBW a total cash fee which is currently estimated to be approximately$6.8 million, $650,000 of which became payable to KBW with the rendering of its opinion(regardless of the conclusion reached in KBW’s opinion), and the balance of which is contingent upon the closing of the merger.