TRex Bio CEO reports four stock-option holdings

TRXB's chief executive officer has one fully vested option position; the other reported options vest monthly subject to continued service.

Rhea-AI Filing Summary

As of October 8, 2026, TRex Bio, Inc. (TRXB) Chief Executive Officer and director Marion Johnston Erwin Jr. reported direct holdings of stock options covering 299,491 shares at $1.09, 126,681 shares at $1.09, 459,613 shares at $1.24, and 257,266 shares at $1.28. They expire on November 22, 2031; May 24, 2035; April 10, 2035; and February 18, 2036, respectively. The first option is fully vested and exercisable; the other three vest in monthly installments subject to continued service.

Insider Trade Summary

4 transactions reported

Mixed 4 txns

Insider Erwin Marion Johnston Jr.

Role Chief Executive Officer

Type	Security	Shares	Price	Value
holding	Stock Option (Right to Buy) F1	--	--	--
holding	Stock Option (Right to Buy) F2	--	--	--
holding	Stock Option (Right to Buy) F3	--	--	--
holding	Stock Option (Right to Buy) F4	--	--	--

Holdings After Transaction: Stock Option (Right to Buy) — 1,143,051 contracts (Direct)

Footnotes (4)

1. F1. The option is fully vested and exercisable as of the date hereof.
2. F2. The option had a vesting start date of May 25, 2022. 25% of the options vested on May, 25, 2023, and vests in equal monthly installments over 36 months, subject to continued service through the applicable vesting dates.
3. F3. The option had a vesting start date of April 1, 2025 and vests in equal monthly installments over 48 months, subject to continued service through the applicable vesting dates.
4. F4. The option had a vesting start date of February 19, 2026 and vests in equal monthly installments over 48 months, subject to continued service through the applicable vesting dates.

Key Figures

Underlying shares: 299,491 shares Exercise price: $1.09 per share Underlying shares: 126,681 shares +5 more

8 metrics

Underlying shares 299,491 shares Stock option at $1.09; expires November 22, 2031; fully vested and exercisable.

Exercise price $1.09 per share Stock option covering 299,491 underlying shares; expires November 22, 2031.

Underlying shares 126,681 shares Stock option at $1.09; expires May 24, 2035.

Exercise price $1.09 per share Stock option covering 126,681 underlying shares; expires May 24, 2035.

Underlying shares 459,613 shares Stock option at $1.24; expires April 10, 2035.

Exercise price $1.24 per share Stock option covering 459,613 underlying shares; expires April 10, 2035.

Underlying shares 257,266 shares Stock option at $1.28; expires February 18, 2036.

Exercise price $1.28 per share Stock option covering 257,266 underlying shares; expires February 18, 2036.

Key Terms

Stock Option (Right to Buy), fully vested and exercisable, equal monthly installments, continued service

4 terms

Stock Option (Right to Buy) technical

"Stock Option (Right to Buy)"

fully vested and exercisable technical

"The option is fully vested and exercisable"

equal monthly installments technical

"vests in equal monthly installments over 36 months"

continued service technical

"subject to continued service through the applicable vesting dates"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What stock options did TRXB's CEO report?

The four direct stock-option holdings cover 299,491 shares at $1.09, 126,681 shares at $1.09, 459,613 shares at $1.24, and 257,266 shares at $1.28. Their expiration dates are November 22, 2031, May 24, 2035, April 10, 2035, and February 18, 2036, respectively.

What are the vesting terms for TRXB's CEO's reported options?

The 299,491-share option was fully vested and exercisable as of October 8, 2026. The 126,681-share option began vesting May 25, 2022, with 25% vesting May 25, 2023, and equal monthly installments over 36 months. The 459,613- and 257,266-share options vest in equal monthly installments over 48 months from April 1, 2025, and February 19, 2026, respectively, subject to continued service through the applicable vesting dates.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 10/13/2026 - 08:15 PM EDT Accepted by SEC EDGAR 10/08/2026 - 09:43 PM EDT Learn about SEC filing dates

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0104
Estimated average burden
hours per response:			0.5

1. Name and Address of Reporting Person^*

Erwin Marion Johnston Jr.

(Last) (First) (Middle)

C/O TREX BIO, INC.

269 EAST GRAND AVENUE, SUITE 300

(Street)

SOUTH SAN FRANCISCO CALIFORNIA 94080

(City) (State) (Zip)

UNITED STATES

(Country)

2. Date of Event Requiring Statement (Month/Day/Year)
10/08/2026

3. Issuer Name and Ticker or Trading Symbol
TRex Bio, Inc. [ TRXB ]

3a. Foreign Trading Symbol

5. If Amendment, Date of Original Filed (Month/Day/Year)

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Executive Officer

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (Right to Buy)	(1)	11/22/2031	Common Stock	299,491	$1.09	D
Stock Option (Right to Buy)	(2)	05/24/2035	Common Stock	126,681	$1.09	D
Stock Option (Right to Buy)	(3)	04/10/2035	Common Stock	459,613	$1.24	D
Stock Option (Right to Buy)	(4)	02/18/2036	Common Stock	257,266	$1.28	D

Explanation of Responses:

1. The option is fully vested and exercisable as of the date hereof.

2. The option had a vesting start date of May 25, 2022. 25% of the options vested on May, 25, 2023, and vests in equal monthly installments over 36 months, subject to continued service through the applicable vesting dates.

3. The option had a vesting start date of April 1, 2025 and vests in equal monthly installments over 48 months, subject to continued service through the applicable vesting dates.

4. The option had a vesting start date of February 19, 2026 and vests in equal monthly installments over 48 months, subject to continued service through the applicable vesting dates.

Remarks:

Exhibit List: Exhibit 24 - Power of Attorney

	/s/ Brandon Hants, Attorney-in-Fact	10/08/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 3: SEC 1473 (03-26)