Paragon Agreements	9 Months Ended
Sep. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Paragon Agreements	9. Paragon Agreements Paragon Antibody Discovery and Option Agreement In September 2025, the Company entered into the Paragon ADOA with Paragon and Parasa. Under the Paragon ADOA, Paragon identifies, evaluates, and develops antibodies against one or more mutually agreed therapeutic targets and a mutually agreed brain transit target. The Paragon ADOA covers Research Program 001 and Research Program 002, each targeting Ab and TfR1 (together the “Ab program”), and one undisclosed research program 003, with the ability to add additional programs by mutual agreement. The Company’s lead product candidate, KRSA-028, was developed from program 002. Under the Paragon ADOA, Korsana has the exclusive option (each, an “ADOA Option”), on a Program-by-Program basis, to enter into a separate agreement with Paragon consistent with a set of pre-negotiated terms to further develop, manufacture and commercialize the resulting antibody transport vehicle compounds (each, a “License Agreement”). If the Company exercises an ADOA Option and finalizes a related License Agreement, it will be required on a program-by-program and product-by-product basis, to make one-time, non-refundable milestone payments of up to $46.0 million per product upon the achievement of specified clinical development and regulatory milestones, which amount is reduced by 50% for independently developed products directed to the same target combination. Additionally, the Company will be required to make tiered royalty payments in the low-to-mid single-digits beginning on the first commercial sale of each developed product. From time to time, the Company can choose to add additional targets by mutual agreement with Paragon. On March 19, 2026, the Company exercised its ADOA Option for Research Program 002. The Company made a $5.0 million milestone payment to Paragon in March 2026 related to the nomination of KRSA-028 as the development candidate for Research Program 002. On June 8, 2026, the Company entered into a license agreement (the "Paragon License Agreement") with respect to the Ab program. The $5.0 million milestone payment made to Paragon in March 2026 related to the nomination of KRSA-028 as the development candidate for Research Program 002 will not be owed again under the Paragon License Agreement. Under the terms of the Paragon ADOA, Paragon agreed to perform certain research activities to discover, generate, identify, and characterize one or more antibody candidates directed to certain mutually agreed therapeutic targets of interest to Korsana (each, a “Research Program”), and certain administrative activities. The Paragon ADOA requires Korsana, Paragon, and Parasa to develop a research plan for each target that includes design, modelling, synthesis, evaluation, and other mutually agreed activities (each, a “Research Plan”), which activities may include performing preclinical studies. Korsana is required to pay a one-time non-refundable, non-creditable fee of $1.0 million (the “Research Initiation Fee”) within 30 days following finalization of the Research Plan for each such Research Program. Paragon will perform the activities set forth in each Research Plan on the timelines set forth in such Research Plan and in compliance with a mutually agreed budget. Korsana will reimburse Paragon for the costs of performing the development activities set forth in the Research Plan, plus an agreed-upon margin charged by Paragon. Korsana made an upfront payment to Paragon when they entered into the Paragon ADOA to cover the cost of work completed by Paragon for the selected Research Programs prior to the effective date. Each Research Program is overseen and coordinated by a joint development committee consisting of two employees from Korsana and two employees from Paragon, with Korsana and Paragon each having one vote with respect to decisions of the committee. When Paragon and Parasa have produced an antibody against a selected target, and upon the completion of each Research Program, Paragon and Parasa will deliver to Korsana a data package that includes sequence information for all then-existing antibodies and information directed to such target. Unless terminated earlier, the Paragon ADOA shall continue in force on a Research Program-by-Research Program basis until the later of: (i) the end of the Option Period for such Research Program, as applicable, if such Option is not exercised by the Company; (ii) if the Company exercises its Option with respect to a Research Program, but the parties are unable to finalize and execute a License Agreement within 30 days, the expiration of such 30-day period (subject to any mutually agreed extension of such period); and (iii) the expiration of the applicable Research Term (as defined under the Paragon ADOA). The Company may terminate the Paragon ADOA or any Research Program at any time for any or no reason upon 30 days’ prior written notice to Paragon, provided that the Company must pay certain unpaid fees due to Paragon upon such termination, as well as any non-cancellable obligations reasonably incurred by Paragon in connection with its activities under any terminated Research Program. Paragon may terminate the Paragon ADOA or a Research Program immediately upon written notice to the Company if, as a result of any action or failure to act by the Company or its affiliates, such Research Program or all material activities under the applicable Research Plan are suspended, discontinued or otherwise delayed for a certain consecutive number of months. Each party has the right to terminate the Paragon ADOA or any Research Program upon (i) 30 days’ prior written notice of the other party’s material breach that remains uncured for the 30-day period and (ii) the other party’s bankruptcy. Any License Agreement entered into with respect to a given Research Program shall contain the same milestone payment obligations as the Paragon ADOA, provided that any milestone set in the Paragon ADOA that has not yet been achieved and is duplicated in such License Agreement shall no longer be achievable and payable under the terms of the Paragon ADOA and shall only be achievable under the terms of the License Agreement. For the avoidance of doubt, if a milestone is achieved and paid by Korsana pursuant to the Paragon ADOA for a certain Research Program, then there shall be no milestone payment due for the achievement of such milestone under a subsequently executed License Agreement for such Research Program. Further, under a License Agreement, Korsana would also be required to make royalty payments to Paragon in the low single-digit percentage range based on net sales of products, subject to certain reductions. The royalty term will terminate on a product-by-product and country-by-country basis upon the later of the expiration of the last-to-expire valid claim within the relevant patent rights or the twelfth anniversary of the first commercial sale of such product in such country. Under the Paragon ADOA, Korsana granted on December 31, 2025 and will grant on December 31, 2026, Parasa warrants to purchase a number of shares equal to 1.00% of Korsana’s outstanding capital stock as of the date of the grant on a fully-diluted basis, with an exercise price equal to the fair market value of the underlying shares of Korsana common stock on each respective grant date. Parasa is an entity formed by Paragon as a vehicle to hold equity in Korsana in order to share profits with certain employees of Paragon and will not perform any substantive role under the Paragon ADOA other than to receive such warrants (see Note 7). The Company concluded that the rights obtained under the Paragon ADOA represent an asset acquisition whereby the underlying assets comprise in-process research and development assets with no alternative future use. The Paragon ADOA did not qualify as a business combination because substantially all of the fair value of the assets acquired was concentrated in the in-process research and development assets, which represent a group of similar identifiable assets. All of the upfront consideration paid by Korsana was allocated to the in-process research and development assets acquired and was immediately expensed as part of research and development expenses on the condensed consolidated statement of operations and comprehensive loss. The research initiation fees represent a one-time cost on a research program-by-research program basis for accessing research services or resources with benefits that are expected to be consumed in the near term, therefore the amounts paid are expensed as part of research and development costs immediately. Amounts paid as reimbursements of on-going development costs, monthly development cost fees and additional development expenses incurred by Paragon are recognized as research and development expense when incurred. Amounts paid as reimbursements for administrative activities incurred by Paragon are recognized as general and administrative expense when incurred. Under the Paragon ADOA, the Company recorded total expense of $35.5 million during the nine months ended September 30, 2026 for amounts owed to Paragon across all Research Programs, including $16.0 million of research and development work completed by Paragon, $5.0 million for the achievement of a development candidate milestone, $1.0 million for the research initiation milestone, and $13.5 million of stock-based compensation expense related to the 2026 Parasa Warrant Obligation. The Company recorded total expense of $20.3 million for the three months ended September 30, 2026 for amounts owed to Paragon across all Research Programs, including $7.6 million of research and development work completed by Paragon and $12.7 million of stock-based compensation expense related to the 2026 Parasa Warrant Obligation. An amount of $7.6 million and $10.6 million was unpaid by Korsana at September 30, 2026 and December 31, 2025, respectively, and is included in related party accrued expenses and other current liabilities within the Company’s condensed consolidated balance sheet. Further, an amount of $13.5 million related to the 2026 Parasa Warrant Obligation is included in warrant liability, related party within the Company’s condensed consolidated balance sheet. Paragon Platform Option Agreement In October 2025, the Company entered into the Platform Option Agreement with Paragon and Parasa (the “Paragon POA”) in connection with the Paragon ADOA. Pursuant to the Paragon POA, the Company will have an exclusive option to enter into either a separate Antibody Discovery and Option Agreement or a separate License Agreement with Paragon and Parasa, enabling the Company with the right to add, remove, or replace specific target combinations and further develop, manufacture and commercialize the resulting antibody transport vehicle compounds. Following designation of a target combination, the Company may elect their option to enter into a separate Antibody Discovery and Option Agreement or a separate License Agreement with Paragon and Parasa, the terms of which will be finalized in connection with the option exercise. If the Company elects to enter into a License Agreement (a “POA License”), it will be required to make a one-time non-refundable payment to Paragon of $5.0 million for the license option exercise fee. Under any POA License, Korsana would be required to make one-time, non-refundable milestone payments of up to $41.0 million per product, reduced by 50% for independently developed products directed to the same target combination, and tiered royalty payments in the low to mid-single digit percentage range based on annual net sales, subject to certain reductions. These payments are intended to fund the research to be performed by Paragon and Parasa under either an Antibody Discovery and Option Agreement or License Agreement. The Company recorded total expense of $1.4 million during the three and nine months ended September 30, 2026 for research and development work completed by Paragon. An amount of $1.4 million was unpaid by Korsana at September 30, 2026 and is included in related party accrued expenses and other current liabilities within the Company's condensed consolidated balance sheet. As of September 30, 2026, the Company has not exercised its option related to the Paragon POA. The Company will also have an exclusive option to designate up to two additional reserved target combinations. If the Company exercises its option, it will be required to make a one-time non-refundable payment to Paragon of $2.0 million for the additional reserved target option exercise fee. A separate additional reserved target option exercise fee is due and payable to Paragon each time that the Company exercises an additional reserved target option. Paragon Antibody Oligo Conjugate Research Letter Agreement In April 2026, the Company entered into an Antibody Oligo Conjugate Research Letter Agreement (the “Paragon Research Letter Agreement”) with Paragon Laboratories, Inc. (“Paragon Laboratories”) to initiate a Research Program focused on the development of antibody oligonucleotide conjugates directed to a selected target. The Paragon Research Letter Agreement provides for reimbursement of research costs and monthly research fees, and grants the Company an exclusive option to enter into either an antibody oligonucleotide conjugate discovery and option agreement for an upfront research initiation fee of $1.0 million, or a license agreement for the Research Program for an upfront license fee of $5.0 million. Under the Paragon Research Letter Agreement with Paragon Laboratories, the Company recorded total expense of $3.0 million during the nine months ended September 30, 2026 for amounts owed to Paragon Laboratories, including $3.0 million of research and development work completed by Paragon Laboratories. The Company recorded total expense of $2.0 million for the three months ended September 30, 2026 for amounts owed to Paragon Laboratories, including $2.0 million of research and development work completed by Paragon Laboratories. An amount of $2.0 million was unpaid by Korsana at September 30, 2026 and is included in related party accrued expenses and other current liabilities within the Company’s condensed consolidated balance sheet. At this time, the Company has not exercised either option related to the Research Letter Agreement.

Paragon Agreements

9 Months Ended

Sep. 30, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

9. Paragon Agreements

Paragon Antibody Discovery and Option Agreement

In September 2025, the Company entered into the Paragon ADOA with Paragon and Parasa. Under the Paragon ADOA, Paragon identifies, evaluates, and develops antibodies against one or more mutually agreed therapeutic targets and a mutually agreed brain transit target. The Paragon ADOA covers Research Program 001 and Research Program 002, each targeting Ab and TfR1 (together the “Ab program”), and one undisclosed research program 003, with the ability to add additional programs by mutual agreement. The Company’s lead product candidate, KRSA-028, was developed from program 002.

Under the Paragon ADOA, Korsana has the exclusive option (each, an “ADOA Option”), on a Program-by-Program basis, to enter into a separate agreement with Paragon consistent with a set of pre-negotiated terms to further develop, manufacture and commercialize the resulting antibody transport vehicle compounds (each, a “License Agreement”). If the Company exercises an ADOA Option and finalizes a related License Agreement, it will be required on a program-by-program and product-by-product basis, to make one-time, non-refundable milestone payments of up to $46.0 million per product upon the achievement of specified clinical development and regulatory milestones, which amount is reduced by 50% for independently developed products directed to the same target combination. Additionally, the Company will be required to make tiered royalty payments in the low-to-mid single-digits beginning on the first

commercial sale of each developed product. From time to time, the Company can choose to add additional targets by mutual agreement with Paragon.

On March 19, 2026, the Company exercised its ADOA Option for Research Program 002. The Company made a $5.0 million milestone payment to Paragon in March 2026 related to the nomination of KRSA-028 as the development candidate for Research Program 002. On June 8, 2026, the Company entered into a license agreement (the "Paragon License Agreement") with respect to the Ab program. The $5.0 million milestone payment made to Paragon in March 2026 related to the nomination of KRSA-028 as the development candidate for Research Program 002 will not be owed again under the Paragon License Agreement.

Under the terms of the Paragon ADOA, Paragon agreed to perform certain research activities to discover, generate, identify, and characterize one or more antibody candidates directed to certain mutually agreed therapeutic targets of interest to Korsana (each, a “Research Program”), and certain administrative activities. The Paragon ADOA requires Korsana, Paragon, and Parasa to develop a research plan for each target that includes design, modelling, synthesis, evaluation, and other mutually agreed activities (each, a “Research Plan”), which activities may include performing preclinical studies. Korsana is required to pay a one-time non-refundable, non-creditable fee of $1.0 million (the “Research Initiation Fee”) within 30 days following finalization of the Research Plan for each such Research Program. Paragon will perform the activities set forth in each Research Plan on the timelines set forth in such Research Plan and in compliance with a mutually agreed budget. Korsana will reimburse Paragon for the costs of performing the development activities set forth in the Research Plan, plus an agreed-upon margin charged by Paragon. Korsana made an upfront payment to Paragon when they entered into the Paragon ADOA to cover the cost of work completed by Paragon for the selected Research Programs prior to the effective date. Each Research Program is overseen and coordinated by a joint development committee consisting of two employees from Korsana and two employees from Paragon, with Korsana and Paragon each having one vote with respect to decisions of the committee. When Paragon and Parasa have produced an antibody against a selected target, and upon the completion of each Research Program, Paragon and Parasa will deliver to Korsana a data package that includes sequence information for all then-existing antibodies and information directed to such target.

Unless terminated earlier, the Paragon ADOA shall continue in force on a Research Program-by-Research Program basis until the later of: (i) the end of the Option Period for such Research Program, as applicable, if such Option is not exercised by the Company; (ii) if the Company exercises its Option with respect to a Research Program, but the parties are unable to finalize and execute a License Agreement within 30 days, the expiration of such 30-day period (subject to any mutually agreed extension of such period); and (iii) the expiration of the applicable Research Term (as defined under the Paragon ADOA). The Company may terminate the Paragon ADOA or any Research Program at any time for any or no reason upon 30 days’ prior written notice to Paragon, provided that the Company must pay certain unpaid fees due to Paragon upon such termination, as well as any non-cancellable obligations reasonably incurred by Paragon in connection with its activities under any terminated Research Program. Paragon may terminate the Paragon ADOA or a Research Program immediately upon written notice to the Company if, as a result of any action or failure to act by the Company or its affiliates, such Research Program or all material activities under the applicable Research Plan are suspended, discontinued or otherwise delayed for a certain consecutive number of months. Each party has the right to terminate the Paragon ADOA or any Research Program upon (i) 30 days’ prior written notice of the other party’s material breach that remains uncured for the 30-day period and (ii) the other party’s bankruptcy.

Any License Agreement entered into with respect to a given Research Program shall contain the same milestone payment obligations as the Paragon ADOA, provided that any milestone set in the Paragon ADOA that has not yet been achieved and is duplicated in such License Agreement shall no longer be achievable and payable under the terms of the Paragon ADOA and shall only be achievable under the terms of the License Agreement. For the avoidance of doubt, if a milestone is achieved and paid by Korsana pursuant to the Paragon ADOA for a certain Research Program, then there shall be no milestone payment due for the achievement of such milestone under a subsequently executed License Agreement for such Research Program. Further, under a License Agreement, Korsana would also be required to make royalty payments to Paragon in the low single-digit percentage range based on net sales of products, subject to certain reductions. The royalty term will terminate on a product-by-product and country-by-country basis upon the later of the expiration of the last-to-expire valid claim within the relevant patent rights or the twelfth anniversary of the first commercial sale of such product in such country.

Under the Paragon ADOA, Korsana granted on December 31, 2025 and will grant on December 31, 2026, Parasa warrants to purchase a number of shares equal to 1.00% of Korsana’s outstanding capital stock as of the date of the grant on a fully-diluted basis, with an exercise price equal to the fair market value of the underlying shares of Korsana common stock on each respective grant date. Parasa is an entity formed by Paragon as a vehicle to hold equity in Korsana in order to share profits with certain employees of Paragon and will not perform any substantive role under the Paragon ADOA other than to receive such warrants (see Note 7).

The Company concluded that the rights obtained under the Paragon ADOA represent an asset acquisition whereby the underlying assets comprise in-process research and development assets with no alternative future use. The Paragon ADOA did not qualify as a business combination because substantially all of the fair value of the assets acquired was concentrated in the in-process research and development assets, which represent a group of similar identifiable assets. All of the upfront consideration paid by Korsana was allocated to the in-process research and development assets acquired and was immediately expensed as part of research and development expenses on the condensed consolidated statement of operations and comprehensive loss. The research initiation fees represent a one-time cost on a research program-by-research program basis for accessing research services or resources with benefits that are expected to be consumed in the near term, therefore the amounts paid are expensed as part of research and development costs immediately. Amounts paid as reimbursements of on-going development costs, monthly development cost fees and additional development expenses incurred by Paragon are recognized as research and development expense when incurred. Amounts paid as reimbursements for administrative activities incurred by Paragon are recognized as general and administrative expense when incurred.

Under the Paragon ADOA, the Company recorded total expense of $35.5 million during the nine months ended September 30, 2026 for amounts owed to Paragon across all Research Programs, including $16.0 million of research and development work completed by Paragon, $5.0 million for the achievement of a development candidate milestone, $1.0 million for the research initiation milestone, and $13.5 million of stock-based compensation expense related to the 2026 Parasa Warrant Obligation. The Company recorded total expense of $20.3 million for the three months ended September 30, 2026 for amounts owed to Paragon across all Research Programs, including $7.6 million of research and development work completed by Paragon and $12.7 million of stock-based compensation expense related to the 2026 Parasa Warrant Obligation. An amount of $7.6 million and $10.6 million was unpaid by Korsana at September 30, 2026 and December 31, 2025, respectively, and is included in related party accrued expenses and other current liabilities within the Company’s condensed consolidated balance sheet. Further, an amount of $13.5 million related to the 2026 Parasa Warrant Obligation is included in warrant liability, related party within the Company’s condensed consolidated balance sheet.

Paragon Platform Option Agreement

In October 2025, the Company entered into the Platform Option Agreement with Paragon and Parasa (the “Paragon POA”) in connection with the Paragon ADOA. Pursuant to the Paragon POA, the Company will have an exclusive option to enter into either a separate Antibody Discovery and Option Agreement or a separate License Agreement with Paragon and Parasa, enabling the Company with the right to add, remove, or replace specific target combinations and further develop, manufacture and commercialize the resulting antibody transport vehicle compounds.

Following designation of a target combination, the Company may elect their option to enter into a separate Antibody Discovery and Option Agreement or a separate License Agreement with Paragon and Parasa, the terms of which will be finalized in connection with the option exercise. If the Company elects to enter into a License Agreement (a “POA License”), it will be required to make a one-time non-refundable payment to Paragon of $5.0 million for the license option exercise fee. Under any POA License, Korsana would be required to make one-time, non-refundable milestone payments of up to $41.0 million per product, reduced by 50% for independently developed products directed to the same target combination, and tiered royalty payments in the low to mid-single digit percentage range based on annual net sales, subject to certain reductions. These payments are intended to fund the research to be performed by Paragon and Parasa under either an Antibody Discovery and Option Agreement or License Agreement. The Company recorded total expense of $1.4 million during the three and nine months ended September 30, 2026 for research and development work completed by Paragon. An amount of $1.4 million was unpaid by Korsana at September 30, 2026 and is included in related party accrued expenses and other current liabilities within the Company's condensed consolidated balance sheet. As of September 30, 2026, the Company has not exercised its option related to the Paragon POA.

The Company will also have an exclusive option to designate up to two additional reserved target combinations. If the Company exercises its option, it will be required to make a one-time non-refundable payment to Paragon of $2.0 million for the additional reserved target option exercise fee. A separate additional reserved target option exercise fee is due and payable to Paragon each time that the Company exercises an additional reserved target option.

Paragon Antibody Oligo Conjugate Research Letter Agreement

In April 2026, the Company entered into an Antibody Oligo Conjugate Research Letter Agreement (the “Paragon Research Letter Agreement”) with Paragon Laboratories, Inc. (“Paragon Laboratories”) to initiate a Research Program focused on the development of antibody oligonucleotide conjugates directed to a selected target. The Paragon Research Letter Agreement provides for reimbursement of research costs and monthly research fees, and grants the Company an exclusive option to enter into either an antibody oligonucleotide conjugate discovery and option agreement for an upfront research initiation fee of $1.0 million, or a license agreement for the Research

Program for an upfront license fee of $5.0 million. Under the Paragon Research Letter Agreement with Paragon Laboratories, the Company recorded total expense of $3.0 million during the nine months ended September 30, 2026 for amounts owed to Paragon Laboratories, including $3.0 million of research and development work completed by Paragon Laboratories. The Company recorded total expense of $2.0 million for the three months ended September 30, 2026 for amounts owed to Paragon Laboratories, including $2.0 million of research and development work completed by Paragon Laboratories. An amount of $2.0 million was unpaid by Korsana at September 30, 2026 and is included in related party accrued expenses and other current liabilities within the Company’s condensed consolidated balance sheet. At this time, the Company has not exercised either option related to the Research Letter Agreement.