ASP Isotopes CFO sells 23,124 shares in tax trade

ASP Isotopes Inc. Chief Financial Officer Heather Kiessling reported an open-market sale of 23,124 shares of common stock on April 15, 2026 at a weighted average price of $5.478 per share.

Rhea-AI Filing Summary

ASP Isotopes Inc. Chief Financial Officer Heather Kiessling reported an open-market sale of 23,124 shares of common stock on April 15, 2026 at a weighted average price of $5.478 per share. The footnotes state this was a "sell to cover" under a Rule 10b5-1 trading plan adopted on December 19, 2025 to cover tax withholding obligations tied to vesting restricted stock awards. After the sale, she directly holds 709,376 shares of ASP Isotopes common stock.

Insider Trade Summary 10b5-1

Net Seller: 23,124 shares

Net Sell 1 txn

Insider Kiessling Heather

Role Chief Financial Officer

Sold 23,124 shs ($127K)

Type	Security	Shares	Price	Value
Sale	Common Stock	23,124	$5.478	$127K

Holdings After Transaction: Common Stock — 709,376 shares (Direct)

Footnotes (2)

1. F1. Represents "sell to cover" sales effected pursuant to a Rule 10b5-1 trading plan adopted by the filing person on December 19, 2025 to cover tax withholding obligations in connection with the vesting of restricted stock awards.
2. F2. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $5.12 to $5.71, inclusive. The reporting person undertakes to provide ASP Isotopes Inc. (the "Company"), any stockholder of the Company, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in Footnote 2.

Key Figures

Shares sold: 23,124 shares Weighted average sale price: $5.478 per share Sale price range: $5.12 to $5.71 per share +2 more

5 metrics

Shares sold 23,124 shares Open-market sale on April 15, 2026

Weighted average sale price $5.478 per share Common stock sale on April 15, 2026

Sale price range $5.12 to $5.71 per share Multiple transactions within reported sale

Shares held after transaction 709,376 shares Direct holdings after April 15, 2026 sale

Trading plan adoption date December 19, 2025 Rule 10b5-1 trading plan used for this sale

Key Terms

Rule 10b5-1 trading plan, sell to cover, restricted stock awards, weighted average price

4 terms

Rule 10b5-1 trading plan regulatory

"sales effected pursuant to a Rule 10b5-1 trading plan adopted by the filing person"

A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.

sell to cover financial

"Represents "sell to cover" sales effected pursuant to a Rule 10b5-1 trading plan"

Sell to cover is when a person who receives company stock through options or awards sells just enough shares immediately to pay required taxes, exercise costs, or fees, keeping the rest. Think of it like cashing part of a bonus to cover the tax bill so you can keep the remainder. For investors, it can create predictable small selling pressure and slightly change the number of shares actually held by insiders without increasing long‑term dilution.

restricted stock awards financial

"tax withholding obligations in connection with the vesting of restricted stock awards"

Restricted stock awards are company shares given to employees or executives that cannot be sold or transferred until certain conditions — like staying with the company for a set time or meeting performance targets — are met, like a gift that is locked in a safe until rules are satisfied. Investors care because these awards tie management’s pay to company performance, can increase the number of shares outstanding when they become tradable (dilution), and may signal expected future selling pressure or commitment to long-term growth.

weighted average price financial

"The price reported in Column 4 is a weighted average price."

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

FAQ

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

What insider transaction did ASP Isotopes (ASPI) disclose for its CFO?

ASP Isotopes disclosed that CFO Heather Kiessling sold 23,124 shares of common stock on April 15, 2026. The sale was reported as an open-market transaction primarily to cover tax withholding obligations linked to vesting restricted stock awards.

At what price did the ASP Isotopes (ASPI) CFO sell her shares?

The CFO’s sale used a weighted average price of $5.478 per share. Footnotes explain the shares were sold in multiple trades at prices ranging from $5.12 to $5.71, with detailed breakdowns available on request.

Why were ASP Isotopes (ASPI) CFO’s shares sold according to the Form 4?

The filing notes the sales were “sell to cover” transactions under a Rule 10b5-1 trading plan. They were made specifically to cover tax withholding obligations arising from the vesting of restricted stock awards granted to the CFO.

How many ASP Isotopes (ASPI) shares does the CFO hold after the sale?

After completing the reported sale, CFO Heather Kiessling directly holds 709,376 shares of ASP Isotopes common stock. This post-transaction holding figure is disclosed in the Form 4 as the total number of directly owned shares.

Was the ASP Isotopes (ASPI) CFO sale pre-planned under Rule 10b5-1?

Yes. Footnotes state the transactions were executed under a Rule 10b5-1 trading plan adopted on December 19, 2025. Such plans pre-arrange trades, making the timing more routine and tied to a preset schedule rather than discretionary decisions.

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

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Accepted by SEC EDGAR 04/17/2026 - 09:54 PM Learn about SEC filing dates

SEC Form 4

FORM 4

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

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

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:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Kiessling Heather

(Last) (First) (Middle)

C/O ASP ISOTOPES INC.

2200 ROSS AVENUE, SUITE 4575E

(Street)

DALLAS TEXAS 75201

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
ASP Isotopes Inc. [ ASPI ]

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
04/15/2026

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

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

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

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	04/15/2026		S(1)		23,124	D	$5.478(2)	709,376	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. Represents "sell to cover" sales effected pursuant to a Rule 10b5-1 trading plan adopted by the filing person on December 19, 2025 to cover tax withholding obligations in connection with the vesting of restricted stock awards.

2. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $5.12 to $5.71, inclusive. The reporting person undertakes to provide ASP Isotopes Inc. (the "Company"), any stockholder of the Company, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in Footnote 2.

	/s/ Donald Ainscow, as attorney-in-fact	04/17/2026
	** 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 4 (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 4: SEC 1474 (03-26)