Company: GIGGU
Filing Date: 2025-09-29
Form Type: 425
Source: 0001193125-25-221783
Chunk: 23

Company: GigCapital7 Corp.
Filing Date: 2025-09-29
Form: 425
Chunk 23
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 Corp., MMR Merger Sub, Inc., and Hadron Energy, Inc.                                                   
 Sponsor Support Agreement, dated September 27, 2025, by and among GigAcquisitions7 Corp., GigCapital7 Corp. and Hadron Energy, Inc.                                                       |
|:--------|:----|:------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| 10.2    |     | Transaction Support Agreement dated September 27, 2025, by and among GigCapital7 Corp. and certain of the stockholders of Hadron Energy, Inc. named in the Transaction Support Agreement. |
| 99.1    |     | Press Release dated September 29, 2025.                                                                                                                                                   |
| 104     |     | Cover Page Interactive Data File (embedded within the Inline XBRL document).                                                                                                              |

| † | Certain of the exhibits and schedules to this exhibit have been omitted in accordance with Regulation S-K Item 601(b)(2). The Registrant agrees to furnish supplementally a copy of all omitted exhibits and schedules to the SEC upon its request. |

SIGNATURE Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

| Dated: September 29, 2025 |     | GIGCAPITAL7 CORP. 
 By:               |     | /s/ Dr. Avi Katz        |
|:--------------------------|:----|:------------------|:----|:------------------------|
|                           |     | Name:             |     | Dr. Avi S. Katz         |
|                           |     | Title:            |     | Chief Executive Officer |

Exhibit 2.1

Execution Version

DATED SEPTEMBER 27, 2025

BUSINESS COMBINATION AGREEMENT

BY AND AMONG

GIGCAPITAL7 CORP.,

MMR MERGER SUB, INC.

AND

HADRON ENERGY, INC.

TABLE OF CONTENTS

|                                                          |     |                                                |     | Page |    |
| Article I THE TRANSACTIONS                               |     |                                                |     |      |  3 |
| Section 1.01                                             |     | The Domestication                              |     |      |  3 |
| Section 1.02                                             |     | The Merger                                     |     |      |  4 |
| Section 1.03                                             |     | Further Assurances