Side Letter to Biogen Collaboration and License Agreement, by and among the Registrant, Biogen MA Inc. and Biogen International GmbH, dated October 21, 2021

Collaboration and License Agreement between Sage Therapeutics, Inc., (“Sage”) Biogen MA Inc. and Biogen International GmbH (collectively, “Biogen”) (the “Collaboration Agreement”)

“Biogen CMC Know-How” shall mean any Biogen Collaboration Know-How that relates to a modification to the manufacturing process and/or formulation of any of the Licensed Products.

“Biogen CMC Patents” shall mean any Biogen Collaboration Patents that claim any Biogen CMC Know-How.

“Biogen CMC Technology” shall mean Biogen CMC Know-How and Biogen CMC Patents.

Sharing Biogen CMC Know-How: Notwithstanding anything to the contrary in the Collaboration Agreement, Biogen will promptly share copies of all Biogen CMC Know-How with Sage.

License Grant: In addition to the license grants to Sage set forth in the Collaboration Agreement with respect to Licensed Products, Biogen, on behalf of

itself and its Affiliates, hereby grants Sage a non-transferable (except as provided in Section 15.1 (Assignment) of the Collaboration Agreement), sublicensable (through multiple tiers), perpetual, irrevocable, non-exclusive, royalty-free, fully paid-up license under the Biogen CMC Technology to  Exploit any products (excluding any Licensed Product unless it becomes a Terminated Product) in the Field in all countries of the world, provided, however, that Sage may only grant a sublicense of the rights granted by Biogen to Sage under this section (i) to subcontractors engaged by Sage or by any sublicensee permitted under clause (ii) in connection with Exploitation of products containing molecules proprietary to Sage or (ii) in connection with a license or collaboration to develop a molecule proprietary to Sage. The foregoing license will survive the termination of the Collaboration Agreement, in whole or in part, for any reason.  For purposes of this section, the term “Sage” means Sage or any of its Affiliates.

Use of Third Parties: Notwithstanding anything to the contrary in the Collaboration Agreement, in the event Biogen uses a Third Party to perform any Development work with respect to potential modifications to the manufacturing process or formulation for any of the Licensed Products, Biogen will use commercially reasonable efforts to require such Third Party to assign or exclusively license (with the right to sublicense) to Biogen all intellectual property with respect to any such modification developed in the course of performing any such work.