Company: IONQ
Filing Date: 2025-07-07
Form Type: 424B5
Source: 0001193125-25-155901
Chunk: 1

Company: IonQ, Inc.
Filing Date: 2025-07-07
Form: 424B5
Chunk 1
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.” We do not intend to list the Warrants on any exchange. On July 3, 2025, the last reported sale price of our common stock on the NYSE was $44.39 per share.

|                                  |     | Per share(1) |         |     | Per        
 Pre-Funded 
 Warrant    |         |     | Total |                |
|:---------------------------------|:----|:-------------|--------:|:----|:-----------|--------:|:----|:------|---------------:|
| Public offering price            |     | $            | 55.4900 |     | $          | 55.4900 |     | $     | 999,999,994.85 |
| Underwriting discounts(2)        |     | $            |  1.1098 |     | $          |  1.1098 |     | $     |  19,999,999.90 |
| Proceeds, before expenses, to us |     | $            | 54.3802 |     | $          | 54.3802 |     | $     | 979,999,994.95 |

| (1) | The Series A Warrants are being offered for no additional consideration. The above proceeds do not include 
 shares of common stock that may be issued upon the exercise of the Warrants.                               |

| (2) | See “Underwriting” for a description of all underwriting compensation payable in connection with this 
 offering.                                                                                             |

Investing in our common stock involves risks. See “ Risk Factors” beginning on page S-5of 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. Sole Underwriter J.P. Morgan The date of this prospectus supplement is July 7, 2025.

TABLE OF CONTENTS

|                                                   |     | Page |      |
| Prospectus Supplement                             |     |      |      |
| About This Prospectus Supplement                  |     |      | S-1  |
| Prospectus Supplement Summary