As filed with the Securities and Exchange Commission on March 10, 2025
       
      Registration No. 333-259320
      Registration No. 333-270743
       
      
      
        
      UNITED STATES
      SECURITIES AND EXCHANGE COMMISSION
      WASHINGTON, D.C. 20549
       
      POST-EFFECTIVE AMENDMENT NO. 1
      TO
       
      
      FORM S-8 REGISTRATION STATEMENT NO. 333-259320
      FORM S-8 REGISTRATION STATEMENT NO. 333-270743
      
      
      UNDER
      THE SECURITIES ACT OF 1933
       
      
      ATI Physical Therapy, Inc.
      (Exact name of registrant as specified in its charter)
       
      
      
          
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               Delaware 
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               85-1408039 
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               (State or Other Jurisdiction of Incorporation or Organization) 
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               (I.R.S. Employer Identification Number) 
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      2001 Butterfield Rd., Suite 1600
      Downers Grove, IL 60515
      
      
      (Address, including zip code, of registrant’s principal executive offices)
      
      ATI Physical Therapy, Inc. 2021 Equity Incentive Plan
      (Full titles of the plans)
      
       Erik Kantz
      Chief Legal Officer
      2001 Butterfield Rd., Suite 1600
      Downers Grove, IL 60515
      (630) 296-2223
      (Name, address, including zip code, and telephone number, including area code, of agent for service)
      
      Copies to:
      
        Weil, Gotshal & Manges LLP
        767 Fifth Avenue
        New York, NY 10153
        (212) 310-8000
         
        
        
          
       
       
      Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated
        filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.
      
          
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               Large accelerated filer 
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               Accelerated filer 
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               ☐ 
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               Non-accelerated filer 
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            ☒ | 
            
               Smaller reporting company 
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               ☒ 
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               Emerging growth company 
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               ☐ 
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      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 7(a)(2)(B) of the
        Securities Act.  ☐
       
      
      
      
      EXPLANATORY NOTE - DEREGISTRATION OF SECURITIES1
       
      ATI Physical Therapy, Inc., a Delaware corporation (the “Company”), is filing with the Securities and Exchange Commission (the “SEC”) these post-effective amendments (the “Post-Effective Amendments”) to terminate all offerings under the
        following Registration Statements on Form S-8 (the “Effective Registration Statements”) and to withdraw and deregister all shares of Class A common stock, par value $0.0001 per share, of the Company (the “Common Stock”), previously registered under
        the Effective Registration Statements, together with any and all plan interests and other securities registered thereunder:
       
      
          
             
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               Registration Statement No. 333-259320, filed on September 3, 2021, registering the offer and sale of up to an aggregate of 20,728,254 shares of Common Stock issuable under the Company’s 2021 Equity Incentive Plan; and 
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               Registration Statement No. 333-270743, filed on March 22, 2023, registering the offer and sale of up to an aggregate of 37,560,979 shares of Common Stock issuable under the Company’s 2021 Equity Incentive Plan. 
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      On December 4, 2024, the New York Stock Exchange (“NYSE”) filed a Form 25 with the SEC for removal of the Common Stock from listing and registration under Section 12(b) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). The
        Form 25 became effective on December 16, 2024, at which time the Common Stock was automatically delisted from NYSE.
       
      The Company intends to file a Form 15 Certification and Notice of Termination of Registration under Section 12(g) of the Exchange Act and Suspension of Duty to File Reports under Sections 13 and 15(d) of the Exchange Act. In connection
        therewith, the Company has terminated all offerings of its securities pursuant to the Effective Registration Statements. In accordance with the undertakings made by the Company in Part II of the Effective Registration Statements to remove from
        registration, by means of a post-effective amendment, any of the securities that had been registered which remain unsold at the termination of the offering, the Company hereby removes from registration any and all securities registered but unsold
        or otherwise unissued under the Effective Registration Statements as of the date hereof. After giving effect to the Post-Effective Amendments, there will be no remaining securities registered by the Company pursuant to the Effective Registration
        Statements.
      
      
      
      
      1 All pre-June 14, 2023 share and per share dollar amounts herein do not reflect a one-for-fifty reverse-stock split of the Common Stock effected by the Company on June 14, 2023.
       
      
      
      SIGNATURES
       
      Pursuant to the requirements of the Securities Act of 1933, as amended (the “Securities Act”), the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused
        these Post-Effective Amendments to be signed on its behalf by the undersigned, thereunto duly authorized, in the Village of Downers Grove, State of Illinois, on March 10, 2025.
       
       
      
      
          
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               ATI PHYSICAL THERAPY, INC. 
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               By: 
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               Erik Kantz 
              Chief Legal Officer 
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      No other person is required to sign these Post-Effective Amendments in reliance upon Rule 478 under the Securities Act.