Company: IONQ
Filing Date: 2025-02-27
Form Type: 424B5
Source: 0001193125-25-037295
Chunk: 1

Company: IonQ, Inc.
Filing Date: 2025-02-27
Form: 424B5
Chunk 1
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 on our behalf, each sales agent will be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation of the sales agents will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification and contribution to each sales agent with respect to certain liabilities, including liabilities under the Securities Act and the Securities Exchange Act of 1934, as amended (the “Exchange Act”). See “Plan of Distribution” beginning on page S-11for additional information regarding the compensation to be paid to the sales agents. Investing in our common stock involves risks. See “ Risk Factors” beginning on page S-4of this prospectus supplement, page 4 of the accompanying prospectus and “Item 1A—Risk Factors” of our most recent report on Form 10-Kor 10-Qthat is incorporated by reference in this prospectus supplement, before making a decision to invest in our common stock. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement. Any representation to the contrary is a criminal offense.

| Morgan Stanley |     | Needham & Company |

The date of this prospectus supplement is February 26, 2025.

TABLE OF CONTENTS

| Prospectus Supplement               |     | Page |      |
| About this Prospectus Supplement    |     |      | S-ii |
| Prospectus Supplement Summary       |     |      | S-1  |
| The Offering                        |     |      | S-3  |
| Risk Factors                        |     |      | S-4  |
| Forward-Looking Statements          |     |      | S-6  |
| Use of Proceeds                     |     |      | S-8  |
| Dilution                            |     |      | S-9  |
| Plan of Distribution                |     |      | S-11 |
| Legal Matters                       |     |      | S-13 |
| Experts                             |     |      | S-13 |
| Where You Can Find More Information |     |      | S-14 |
| Incorporation by Reference          |     |      | S-15 |

| Prospectus                          |     | Page |    |
| About this Prospectus               |     |      | ii |
| Prospectus Summary                  |     |      |  1 |
| Risk Factors                        |     |      |  4 |
| Forward-Looking