SEC Form 424B3 filed by Nano Nuclear Energy Inc.

Filed Pursuant to Rule 424(b)(3)

Registration No. 333-287562

Prospectus Supplement No. 1 to Reoffer Prospectus

of

NANO NUCLEAR ENERGY INC.

Up to 677,812 Shares of Common Stock under the

Nano Nuclear Energy Inc. 2025 Equity Incentive Plan

This Prospectus Supplement, dated February 20, 2026 (this “Supplement”), supplements the reoffer prospectus (the “Reoffer Prospectus”) filed as part of the Registration Statement on Form S-8 filed by Nano Nuclear Energy Inc. (the “Company”, “us”, “our” or “we”) with the U.S. Securities and Exchange Commission (the “SEC”) on May 23, 2025, relating to the resale of common stock, par value $0.0001 per share (the “Common Stock”), of the Company which may be offered and sold from time to time by certain of our executive officers and directors (the “Selling Stockholders”) who may be deemed “affiliates” of the Company as defined in Rule 405 under the Securities Act of 1933, as amended (the “Securities Act”), who have acquired or will acquire such shares in connection with the exercise of stock options granted, and with stock or other awards made, and with the purchase of stock, under the Company’s 2025 Equity Incentive Plan (the “2025 Plan”). This Supplement covers 677,812 shares of Common Stock (the “Shares”), including (i) shares of Common Stock (inclusive of shares purchased pursuant to the restricted shares granted under the 2025 Plan), and (ii) shares issuable upon vesting of restricted stock units granted to such Selling Stockholders under the 2025 Plan registered pursuant to the Reoffer Prospectus for resale.

You should read this Supplement in conjunction with the Reoffer Prospectus. This Supplement is qualified by reference to the Reoffer Prospectus, except to the extent the information in this Supplement supersedes the information contained in the Reoffer Prospectus.

Our Common Stock is quoted on the Nasdaq Capital Market under the symbol “NNE.” On February 19, 2026, the closing sales price of our Common Stock on the Nasdaq Capital Market was $25.66 per share.

The Shares may be offered for resale from time to time by any or all of the Selling Stockholders, or their permitted transferees, through public or private transactions, at fixed prices, prevailing market prices at the time of sale, prices related to the prevailing market prices, varying prices determined at the time of sale or negotiated prices. See “Plan of Distribution” in the Reoffer Prospectus. Sales may be made through underwriters, broker-dealers or agents, who are expected to receive compensation in the form of discounts, commissions or agent’s commissions. We will not control or determine the price at which a Selling Stockholder decides to sell its shares. Underwriters, brokers or dealers effecting transactions in these shares should confirm that the shares are registered under applicable state law or that an exemption from registration is available.

The Selling Stockholders and participating underwriters, brokers and dealers may be deemed to be “underwriters” within the meaning of the Securities Act, in which event any profit on the sale of shares of those Selling Stockholders and any commissions or discounts received by those underwriters, brokers or dealers may be deemed to be underwriting compensation under the Securities Act.

An investment in our Common Stock is speculative and subject to significant risk. You should carefully read and consider the risk factors under Item 1A beginning on page 27 of our Annual Report on Form 10-K for the year ended September 30, 2025 and Item 1A on page 38 of our Quarterly Report on Form 10-Q for the three months ended December 31, 2025 for risks relating to investment in the Company’s securities.

Neither the SEC nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the Reoffer Prospectus or this Supplement. Any representation to the contrary is a criminal offense.

The information set forth under the caption “Selling Stockholders” in the Reoffer Prospectus is amended and restated in its entirety as set forth below and is provided for the primary purpose of updating the table of the Selling Stockholders contained in the Reoffer Prospectus.

The date of this Supplement is February 20, 2026

SELLING STOCKHOLDERS

The Reoffer Prospectus relates to the offer and sale, from time to time, by the Selling Stockholders named herein, or their permitted transferees, of shares of our Common Stock issued to the Selling Stockholders under the 2025 Plan, as supplemented by this Supplement.

The following table sets forth the names of the Selling Stockholders, the number of shares of Common Stock owned by each of them as of the date of this Supplement, the number of shares of Common Stock that they may offer pursuant to this Supplement, and the number and percentage of shares of Common Stock to be beneficially owned by each Selling Stockholders assuming all of the shares of Common Stock which may be offered by such Selling Stockholders pursuant to this Supplement are sold.

We cannot advise you as to whether the Selling Stockholders will in fact sell any or all of their Common Stock. The Selling Stockholders may offer all or part of the Common Stock for resale from time to time through public or private transactions, at fixed prices, prevailing market prices at the time of sale, prices related to the prevailing market prices, varying prices determined at the time of sale or negotiated prices. Because the Selling Stockholders may offer all, some or none of their securities, no definitive estimate as to the number of shares of Common Stock that will be held by the Selling Stockholders after an offering can be provided. The Selling Stockholders may sell any, all or none of the shares offered by the Reoffer Prospectus, as supplemented by this Supplement. See “Plan of Distribution.” We will not receive any of the proceeds from the sale of the Common Stock sold by the Selling Stockholders.

Beneficial ownership is determined according to the rules of the SEC, which generally provide that a person has beneficial ownership of a security if he, she or it possesses sole or shared voting or investment power over that security. Therefore, beneficial ownership of the Common Stock by each Selling Stockholder includes Common Stock that is currently exercisable, convertible, or exchangeable, or exercisable, convertible, or exchangeable within sixty (60) days.

Unless otherwise indicated, we believe that all persons named in the table below have sole voting and investment power with respect to Common Stock beneficially owned by them.

Selling Stockholder’s information for each additional Selling Stockholder, if any, will be set forth in a prospectus supplement to the extent required prior to the time of any offer or sale of such Selling Stockholder’s Common Stock pursuant to the Reoffer Prospectus, as supplemented by this Supplement. Any future prospectus supplement may add, update, substitute, or change the information contained in the Reoffer Prospectus, as supplemented by this Supplement, including the identity of each Selling Stockholder and the number of shares of Common Stock registered on its behalf .

* Less than one percent (1%)