Filed pursuant to Rule 424(b)(3)
Registration No. 333-257801
Prospectus Supplement No. 1
(to Prospectus dated July 30, 2021)
ATI Physical Therapy, Inc.
196,770,282 shares of Common Stock
Up to 9,866,657 shares of Common Stock Issuable upon Exercise of the Warrants
This prospectus supplement updates and supplements the prospectus dated July 30, 2021 (the Prospectus), which forms a part of our
registration statement on Form S-1 (No. 333-257801). This prospectus supplement is being filed to update and supplement the information in the Prospectus with the information contained in our Current Report on Form 8-K, filed with the
Securities and Exchange Commission on August 9, 2021 (the Current Report), other than the information included in Exhibit 99.1, which was furnished and not filed. Accordingly, we have attached the Current Report to this prospectus
supplement.
This Prospectus and this prospectus supplement relate to: (1) the issuance by us of up to 6,899,991 shares of common
stock, par value $0.0001 per share (Common Stock), of ATI Physical Therapy, Inc., a Delaware corporation (the Company, we, our) that may be issued upon exercise of the Public Warrants (the Public
Warrants) at an exercise price of $11.50 per share, (2) the issuance by us of up to 2,966,666 shares of Common Stock issuable upon the exercise of 2,966,666 warrants (Private Placement Warrants and together with the Public
Warrants, the Warrants) originally issued to the Sponsor (as such term is defined in the Prospectus under Selected Definitions) in a private placement, currently exercisable at a price of $11.50 per Private Placement
Warrant, (2) the offer and sale, from time to time by the selling security holders identified in the Prospectus (the Selling Securityholders), or their permitted transferees of up to 181,770,282 shares of Common Stock currently
outstanding and (3) up to 15,000,000 shares of Common Stock that may be issued in the form of Common Stock pursuant to the earnout provisions of the Merger Agreement.
Our Common Stock and our Public Warrants are listed on the New York Stock Exchange, or NYSE, under the symbol ATIP and
ATIPWS respectively. On August 6, 2021, the last reported sale prices of our Common Stock was $4.38 per share and the last reported sales price of our Public Warrants was $0.92 per warrant.
This prospectus supplement updates and supplements the information in the Prospectus and is not complete without, and may not be delivered or
utilized except in combination with, the Prospectus, including any subsequent amendments or supplements thereto. This prospectus supplement should be read in conjunction with the Prospectus and 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. The information in this prospectus supplement modifies and supersedes, in part, the information in the Prospectus. Any information in
the Prospectus that is modified or superseded shall not be deemed to constitute a part of the Prospectus except as modified or superseded by this prospectus supplement. You should not assume that the information provided in this prospectus
supplement or the Prospectus is accurate as of any date other than their respective dates. Neither the delivery of this prospectus supplement or the Prospectus, nor any sale made hereunder, shall under any circumstances create any implication that
there has been no change in our affairs since the date of this prospectus supplement, or that the information contained in this prospectus supplement or the Prospectus is correct as of any time after the date of that information.
We are an emerging growth company under federal securities laws and are subject to reduced public company reporting
requirements. Investing in our Common Stock involves a high degree of risk. See Risk Factors beginning on page 12 of the Prospectus.
Neither the
Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities nor passed upon the accuracy or adequacy of this Prospectus Supplement No. 1. Any representation to the contrary is a criminal
offense.
The date of this Prospectus Supplement is August 9, 2021