Filed Pursuant to Rule 424(b)(3)

Registration No. 333-215288

PROSPECTUS SUPPLEMENT NO. 4

(to Prospectus dated May 9, 2017)

Vistra Energy Corp.

168,779,076 Shares of Common Stock

This prospectus supplement supplements the prospectus dated May 9, 2017 (as supplemented to date, the Prospectus), which forms a part of our Registration Statement on Form S-1 (Registration No. 333-215288). This prospectus supplement is being filed to update and supplement the information in the Prospectus with information contained in our Current Report on Form 8-K, filed with the Securities and Exchange Commission on July 14, 2017 (the Current Report). Accordingly, we have attached the Current Report to this prospectus supplement.

The Prospectus and this prospectus supplement relate solely to 168,779,076 shares of Vistra Energy Corp. common stock, par value $.01 per share, which we refer to as our common stock or the Vistra Energy common stock, which may be offered for resale from time to time by the stockholders named under the heading “Principal and Selling Stockholders” in the Prospectus, whom we refer to as the selling stockholders. The shares of our common stock offered under the Prospectus, as supplemented by this prospectus supplement, may be resold by the selling stockholders at fixed prices, prevailing market prices at the times of sale, prices related to such prevailing market prices, varying prices determined at the times of sale or negotiated prices and, accordingly, we cannot determine the price or prices at which shares of our common stock may be resold. The shares of our common stock offered by the Prospectus and this prospectus supplement may be resold by the selling stockholders directly to investors or to or through underwriters, dealers or other agents, as described in more detail in the Prospectus. For more information, see the section entitled “Plan of Distribution” in the Prospectus. We do not know if, when or in what amounts a selling stockholder may offer shares of our common stock for resale. The selling stockholders may resell all, some or none of the shares of our common stock offered by the Prospectus, as supplemented by this prospectus supplement, in one or multiple transactions.

This prospectus supplement should be read in conjunction with the Prospectus. This prospectus supplement updates and supplements the information in the Prospectus. If there is any inconsistency between the information in the Prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement.

Our common stock is listed on the New York Stock Exchange, or NYSE, under the symbol “VST.” On July 14, 2017, the closing sales price of our common stock as reported on the NYSE was $16.02 per share.

Investing in our common stock involves risks. Before making a decision to invest in our common stock, you should carefully consider the information referred to under the heading “Risk Factors” beginning on page 21 of the Prospectus.

Neither the Securities and Exchange Commission nor any state or other securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is July 18, 2017.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): July 14, 2017

VISTRA ENERGY CORP.

(Exact name of registrant as specified in its charter)

(214) 812-4600

(Registrant’s telephone number, including area code)

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.   ☐

(d)     On July 14, 2017, upon the recommendation of the Nominating and Governance Committee of the Board of Directors (the Board) of Vistra Energy Corp. (the Company), and in accordance with the Company’s certificate of incorporation and bylaws, the Board increased its size to eight directors and elected Scott Helm to the Board, effective immediately. Mr. Helm will serve as a Class I director of the Board until the expiration of his term on the date of the Company’s annual meeting of stockholders in 2020 and until his successor is elected and qualified. Additionally, upon the recommendation of the Nominating and Governance Committee, the Board approved the appointment of Mr. Helm as a member of the Audit Committee of the Board.

Mr. Helm is a private investor and most recently was a founding partner of Energy Capital Partners, a private equity firm focused on investing in North American energy infrastructure. Prior to founding Energy Capital Partners, from 1998 until 2002, Mr. Helm was executive vice president and chief financial officer of Orion Power Holdings, Inc., a publicly listed company that owned and operated power plants.

There are no arrangements or understandings between Mr. Helm and any other person pursuant to which Mr. Helm was selected as a director of the Company. There are no related person transactions (within the meaning of Item 404(a) of Regulation S-K promulgated by the Securities and Exchange Commission) between Mr. Helm and the Company. In connection with Mr. Helm’s service as a member of the Board and as a member of the Audit Committee of the Board, he will receive a grant of restricted stock units with a grant date fair value of $100,000 based on the public trading price of the Company’s common stock on the date of grant, and will also receive an annual cash retainer of $95,000. In addition to this compensation, Mr. Helm will enter into the Company’s standard form of indemnification agreement with directors, a copy of which is filed as Exhibit 10.26 to Amendment No. 3 to the Company’s Registration Statement on Form S-1 (Registration No. 333-215288), filed with the Securities and Exchange Commission on May 1, 2017, and which is incorporated herein by reference.

SIGNATURES

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