Company: GIGGU
Filing Date: 2025-09-29
Form Type: 425
Source: 0001193125-25-221783
Chunk: 250

Company: GigCapital7 Corp.
Filing Date: 2025-09-29
Form: 425
Chunk 250
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 |     |                         |
| By:              |     | /s/ Dr. Avi Katz        |
| Name:            |     | Dr. Avi S. Katz         |
| Title:           |     | Chief Executive Officer |

6

IN WITNESS WHEREOF, the parties have executed this Agreement as of the date first written above.

| By:                            |     | /s/ Samuel Gibson |
| Name: Samuel Gibson            |     |                   |
| Title: Chief Executive Officer |     |                   |
| Address: ***                   |     |                   |
| Email: ***                     |     |                   |

7

IN WITNESS WHEREOF, the parties have executed this Agreement as of the date first written above.

| By:                            |     | /s/ Mark Kress |
| Name: Mark Kress               |     |                |
| Title: Chief Financial Officer |     |                |
| Address: ***                   |     |                |
| Email: ***                     |     |                |

8

EXHIBIT A Stockholders of Record – Number of Shares

| Stockholder of Record |     | Number of Shares |         |
| Samuel Gibson         |     |                  | 900,000 |
| Mark Kress            |     |                  | 100,000 |

9

EXHIBIT B

Business Combination Agreement

See Attached

10

EXHIBIT C

JOINDER TO TRANSACTION SUPPORT AGREEMENT

This JOINDER TO TRANSACTION SUPPORT AGREEMENT (this “”) is made and entered into as of [•], by and among each
of the stockholders of Hadron Energy, Inc., a Delaware corporation (the “”), whose names appear on the signature pages of this Joinder (each, a “” and, collectively, the
“”), and GigCapital7 Corp., a Cayman Islands exempted company (which shall transfer by way of continuation and domesticate as a Delaware corporation prior to Closing) (“”).

RECITALS

A. GigCapital7
and certain stockholders of the Company have entered into a Transaction Support Agreement dated September [•], 2025 (as amended, modified, supplemented, extended or restated from time to time, the “”) in regard to
the support of the Merger and the other transactions contemplated by the BCA. Capitalized terms used herein but not otherwise defined shall have the meanings set forth in the Agreement.

B. Pursuant to the Agreement, certain stockholders of the Company have agreed, among other