Filed pursuant to Rule 424(b)(3)
Registration No. 333-257801
Prospectus Supplement No. 6
(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 and in the related prospectus
supplements dated August 17, 2021, August 9, 2021, October 7,
2021, October 20, 2021 and November 17, 2021,
respectively, under “Selling Securityholders” with the information
contained herein.
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, (3) 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 (4) 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 December 10, 2021, the last reported sale
prices of our Common Stock was $3.62 per share and the last
reported sales price of our Public Warrants was $0.40 per
warrant.
This prospectus supplement updates and supplements the information
in the Prospectus, including any amendments or supplements thereto,
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,
including any amendments or supplements thereto, and if there is
any inconsistency between the information in the Prospectus, any
prior amendments or supplements thereto, 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,
including any amendments or supplements thereto. Any information in
the Prospectus or any prior amendments or supplements thereto, 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, the Prospectus or any prior
amendments or supplements thereto, is accurate as of any date other
than their respective dates. Neither the delivery of this
prospectus supplement, the Prospectus, any prior amendments or
supplements thereto, 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, the
Prospectus or any prior amendments or supplements thereto, 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. 6. Any representation to the contrary is
a criminal offense.
The date of this Prospectus Supplement is
December 13, 2021