We have certain business and financial rights with respect to RITUXAN for the treatment of non-Hodgkin's lymphoma, CLL and other conditions; RITUXAN HYCELA for the treatment of non-Hodgkin's lymphoma and CLL; GAZYVA for the treatment of CLL, follicular lymphoma and lupus nephritis; OCREVUS for the treatment of PPMS and RMS; LUNSUMIO for the treatment of relapsed or refractory follicular lymphoma; COLUMVI, a bispecific antibody for the treatment of non-Hodgkin's lymphoma; and have the option to add other potential anti-CD20 therapies, pursuant to our collaboration arrangements with Genentech, a wholly owned member of the Roche Group. For purposes of this footnote, we refer to RITUXAN and RITUXAN HYCELA collectively as RITUXAN.

Under our collaboration with Genentech, we are entitled to a tiered share of co-promotion operating profits and losses of RITUXAN in the U.S., as summarized in the table below. Genentech and its affiliates are responsible for the worldwide manufacture of RITUXAN as well as all development and commercialization activities as follows:

The Roche Group and its sub-licensees maintain sole responsibility for the development, manufacture and commercialization of GAZYVA and we are entitled to a tiered share of co-promotion operating profits and losses of GAZYVA in the U.S. The level of gross sales of GAZYVA in the U.S. has impacted our percentage of the co-promotion profits for RITUXAN and LUNSUMIO, as summarized in the table below.

Pursuant to the terms of our collaboration arrangements with Genentech, we receive a tiered royalty on U.S. net sales from 13.5% and increasing up to 24.0% if annual net sales exceed $900.0 million. There will be a 50.0% reduction to these royalties upon the first entry of an FDA-approved biosimilar to OCREVUS.

In addition, we receive a gross 3.0% royalty on net sales of OCREVUS outside the U.S., with the royalty period lasting 11 years from the first commercial sale of OCREVUS on a country-by-country basis.

The commercialization of OCREVUS does not impact the percentage of the co-promotion profits we receive for RITUXAN, LUNSUMIO or GAZYVA. Genentech is solely responsible for development and commercialization of OCREVUS and funding future costs. Genentech cannot develop OCREVUS in CLL, non-Hodgkin's lymphoma or rheumatoid arthritis.

OCREVUS royalty revenue is based on our estimates from third party and market research data of OCREVUS sales occurring during the corresponding period. Differences between actual and estimated royalty revenue will be adjusted for in the period in which they become known, which is generally expected to be the following quarter.

Under our collaboration with Genentech, we are entitled to a tiered share of co-promotion operating profits and losses in the U.S., as summarized in the table below. In addition, we receive low-single digit royalties on sales of LUNSUMIO outside the U.S.

Genentech has sole decision-making rights on the commercialization of COLUMVI within the U.S. and we receive tiered royalties in the mid-single digit range on net sales of COLUMVI in the U.S. The commercialization of COLUMVI does not impact the percentage of the co-promotion profits we receive for RITUXAN, LUNSUMIO or GAZYVA.

Our current pre-tax co-promotion profit-sharing formula for RITUXAN and LUNSUMIO in the U.S. provides for a 30.0% share on the first $50.0 million of combined co-promotion operating profits earned each calendar year. Our share of the combined annual co-promotion profits for RITUXAN and LUNSUMIO in excess of $50.0 million varies upon the following events, as summarized in the table below:

In March 2023 the First Threshold Date was achieved when U.S. gross sales of GAZYVA within a consecutive 12-month period reached $500.0 million. As a result, beginning in April 2023 the pre-tax profit share for RITUXAN and LUNSUMIO has been 35.0%. The Second Threshold Date would be achieved on the first date in any calendar year in which U.S. gross sales of LUNSUMIO have reached $350.0 million.

For additional information on our collaboration arrangements with Genentech, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2025 Form 10-K.

In the second quarter of 2026 we exercised our option with Ionis and obtained a worldwide, exclusive, royalty-bearing license to develop and commercialize a pre-clinical therapy under this agreement. In connection with the option exercise, we made a payment of $15.0 million to Ionis, which was recorded in acquired in-process research and development, upfront and milestone expense within our consolidated statements of income for the three and six months ended June 30, 2026.

In December 2017 we entered into a collaboration agreement with Ionis to identify new ASO drug candidates for the potential treatment of SMA. Under this agreement, we have options to license therapies arising out of this collaboration and will be responsible for the development and commercialization of such therapies.

In December 2021 we exercised our option with Ionis and obtained a worldwide, exclusive, royalty-bearing license to develop and commercialize salanersen (BIIB115), an investigational ASO in development for SMA.

In the second quarter of 2026 we recognized and paid a $45.0 million milestone payment due upon the initiation of a Phase 3 trial in salanersen, which was recorded in acquired in-process research and development, upfront and milestone expense within our consolidated statements of income for the three and six months ended June 30, 2026. Additionally, we may pay Ionis up to $110.0 million in additional development and regulatory milestone payments related to this program. Upon commercialization, we may also pay Ionis up to $400.0 million in additional performance-based milestone payments and tiered royalties on potential net sales of such therapies ranging from the mid-teens to high-twenties percentages.

For additional information on our collaboration arrangements with Ionis, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2025 Form 10-K.

We have a collaboration agreement with Eisai to jointly develop and commercialize LEQEMBI (lecanemab), an anti-amyloid antibody for the treatment of Alzheimer's disease. The FDA granted traditional approval of LEQEMBI in July 2023. Prior to receiving traditional approval, LEQEMBI had been granted accelerated approval by the FDA in January 2023, at which time it became commercially available in the U.S. Outside of the U.S., LEQEMBI is now approved in the E.U. (April 2025), Australia (September 2025), China (January 2024), Japan (September 2023) and other international markets. LEQEMBI monthly IV maintenance dosing for the treatment of early Alzheimer's disease was approved in the U.S. and China in January 2025 and September 2025, respectively, and LEQEMBI subcutaneous autoinjector (IQLIK) for weekly maintenance dosing and initiation dosing was approved in the U.S. in August 2025 and July 2026, respectively.

All costs, including research, development, sales and marketing expense, are shared equally between us and Eisai. We also share profits and losses equally. We currently have a supply agreement with Eisai to manufacture LEQEMBI drug substance and drug product through the end of 2031.

Subject to the limitations in the LEQEMBI Collaboration Agreement, Eisai has final decision-making authority on all matters relating to the collaboration and serves as the lead of LEQEMBI development and regulatory submissions globally. We co-commercialize and co-promote LEQEMBI with Eisai. The LEQEMBI Collaboration Agreement provides that each commercialization plan shall allocate the responsibilities for the activities under the plan in an equitable fashion taking into account Biogen's and Eisai's respective capabilities and provide a meaningful role for each party.

Upon commercialization of LEQEMBI in the U.S., we began recognizing our 50.0% share of LEQEMBI product revenue, net and cost of sales, including royalties, within Alzheimer's collaboration revenue in our condensed consolidated statements of income, as we are not the principal.

Our share of LEQEMBI sales and marketing expense and development expense are recorded within selling, general and administrative expense and research and development expense, respectively, within our condensed consolidated statements of income.


	For the Three Months Ended June 30,				For the Six Months Ended June 30,
(In millions)	2026		2025		2026		2025
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$	61.5	$	54.9	$	130.8	$	107.5
Biogen's share of the LEQEMBI Collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	30.8		27.5		65.4		53.8
Total sales and marketing expense incurred by the LEQEMBI Collaboration	155.2		171.2		324.7		348.9
Biogen's share of the LEQEMBI Collaboration sales and marketing expense reflected in selling, general and administrative expense in our condensed consolidated statements of income	77.6		85.7		162.3		174.5

Amounts receivable from Eisai related to the agreements discussed above were approximately $134.1 million and $90.2 million as of June 30, 2026 and December 31, 2025, respectively. Amounts payable to Eisai related to the agreements discussed above were approximately $92.5 million and $95.5 million as of June 30, 2026 and December 31, 2025, respectively.

For additional information on our collaboration arrangements with Eisai, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2025 Form 10-K.

We have a collaboration agreement with UCB, effective November 2003, to jointly develop and commercialize dapirolizumab pegol, an anti-CD40L pegylated Fab, for the potential treatment of SLE and other future agreed indications. Either we or UCB may propose development of dapirolizumab pegol in additional indications. If the parties do not agree to add an indication as an agreed indication to the collaboration, we or UCB may, at the sole expense of the applicable party, pursue development in such excluded indication(s), subject to an opt-in right of the non-pursuing party after proof of clinical activity.

All costs incurred for agreed indications, including research, development, sales and marketing expense, are shared equally between us and UCB. If marketing approval is obtained, both companies will jointly commercialize dapirolizumab pegol and share profits and losses equally.


	For the Three Months Ended June 30,				For the Six Months Ended June 30,
(In millions)	2026		2025		2026		2025
Total UCB collaboration development expense	$	29.3	$	17.8	$	58.7	$	39.6
Biogen's share of the UCB collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	14.6		8.9		29.3		19.8

In November 2020 we entered into a global collaboration and license agreement with Sage to jointly develop and commercialize ZURZUVAE (zuranolone) for the treatment of PPD. In July 2025 Sage was acquired by Supernus. ZURZUVAE was approved in the U.S. in August 2023 and in the E.U. in September 2025.

Under this collaboration, both companies will share equal responsibility and costs for development as well as profits and losses for commercialization in the U.S. Outside of the U.S., we are responsible for development and commercialization, excluding Japan, Taiwan and South Korea, with respect to zuranolone and may pay Supernus potential tiered royalties in the high-teens to low-twenties percentages.

We share 50.0% of the net collaboration results in the U.S. with Supernus, which are recognized in collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income. For the three and six months ended June 30, 2026, we recognized net profit-sharing expense of approximately $23.9 million and $40.9 million, respectively, to reflect Supernus' 50.0% share of the net collaboration results, compared to net profit-sharing expense of approximately $17.8 million and $27.9 million, respectively, in the prior year comparative periods.


	For the Three Months Ended June 30,				For the Six Months Ended June 30,
(In millions)	2026		2025		2026		2025
Total Supernus collaboration development expense	$	1.2	$	1.5	$	2.4	$	3.9
Biogen's share of the Supernus collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	0.6		0.8		1.2		2.0
Total sales and marketing expense incurred by the Supernus collaboration	53.3		45.7		100.8		89.2
Biogen's share of the Supernus collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income	26.7		22.9		50.4		44.6

In August 2020 we entered into a collaboration and license agreement with Denali to co-develop and co-commercialize BIIB122, a small molecule inhibitor of LRRK2 for Parkinson's disease (LRRK2 Collaboration).

Under the LRRK2 Collaboration, both companies share responsibility and costs for global development based on specified percentages as well as profits and losses for commercialization in the U.S. and China. Outside the U.S. and China we are responsible for commercialization and may pay Denali potential tiered royalties.

In May 2026 Biogen and Denali announced topline results from the Phase 2b LUMA study evaluating BIIB122, which showed that BIIB122 did not meet its primary and secondary endpoints. Based on these results we and Denali will discontinue development of BIIB122 in idiopathic Parkinson's disease.


	For the Three Months Ended June 30,				For the Six Months Ended June 30,
(In millions)	2026		2025		2026		2025
Total Denali collaboration development expense	$	5.5	$	12.1	$	15.8	$	24.9
Biogen's share of the Denali collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	3.3		7.2		9.5		14.9

In February 2025 we entered into a collaboration and license agreement with Stoke to co-develop and commercialize zorevunersen, an investigational ASO that targets the SCN1A gene for the potential treatment of Dravet syndrome, a rare form of genetic epilepsy associated with refractory seizures and neurodevelopmental impairments. Zorevunersen dosed its first patient in August 2025, advancing zorevunersen to a global Phase 3 trial.

Under the terms of this agreement, Stoke will continue to lead global development and retain exclusive development and commercialization rights for zorevunersen in the U.S., Canada and Mexico and we will have exclusive rights to commercialize zorevunersen in the rest of the world. Both companies will share responsibility for external clinical development costs, where Stoke is responsible for 70.0% of these development costs and we are responsible for the remaining 30.0% of these development costs.

In connection with the closing of this transaction we made an upfront payment of $165.0 million to Stoke, which was recognized in acquired in-process research and development, upfront and milestone expense within our condensed consolidated statements of income for the six months ended June 30, 2025. We may also pay Stoke potential development and commercial milestone payments of up to $50.0 million and $335.0 million, respectively, if all the specified milestones set forth in this collaboration are achieved. In addition, we may pay Stoke tiered royalties on potential net sales of any products developed under this collaboration in the low-double digit to high-teen percentages.

We also have an exclusive option to license certain future follow-on ASO products targeting the SCN1A gene in all territories worldwide other than the U.S., Canada and Mexico, in exchange for separate milestone, cost sharing and royalty considerations.


	For the Three Months Ended June 30,				For the Six Months Ended June 30,
(In millions)	2026		2025		2026		2025
Total Stoke collaboration development expense	$	14.3	$	8.9	$	26.5	$	12.8
Biogen's share of the Stoke collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	4.3		2.6		8.0		3.8

In December 2019 we completed a transaction with Samsung Bioepis and secured the exclusive rights to commercialize two potential ophthalmology biosimilar products, BYOOVIZ, a ranibizumab biosimilar referencing LUCENTIS, and OPUVIZ, an aflibercept biosimilar referencing EYLEA, in major markets worldwide, including the U.S., Canada, Europe, Japan and Australia. The agreement established that Samsung Bioepis will be responsible for development and will supply both products to us at a pre-specified gross margin of approximately 45.0%.

In October 2024 we notified Samsung Bioepis of our decision to terminate our 2019 Development and Commercialization Agreement (the DCA Agreement) solely within the U.S. and Canada. The transfer of commercialization rights for BYOOVIZ and OPUVIZ in the U.S. and Canada back to Samsung Bioepis was completed as of December 31, 2025.

In October 2025 we completed the sale of our remaining commercial rights to BYOOVIZ and OPUVIZ in Europe. Samsung Bioepis has full responsibility for commercialization of BYOOVIZ upon the transfer of commercial rights from Biogen back to Samsung Bioepis, which became effective as of January 2026.

We reflected revenue on sales of BYOOVIZ to third parties in product revenue, net in our condensed consolidated statements of income and recorded the related cost of revenue and sales and marketing expense in our condensed consolidated statements of income to their respective line items when these costs are incurred.

In December 2013 we entered into an agreement with Samsung Bioepis to commercialize, over a 10-year term, three anti-TNF biosimilar product candidates which includes IMRALDI, an adalimumab biosimilar referencing HUMIRA, FLIXABI, an infliximab biosimilar referencing REMICADE, and BENEPALI, an etanercept biosimilar referencing ENBREL, in Europe. In July 2024 we exercised an option to extend this agreement by an additional five years.

We reflect revenue on sales of BENEPALI, IMRALDI and FLIXABI to third parties in product revenue, net in our condensed consolidated statements of income and record the related cost of revenue and sales and marketing expense in our condensed consolidated statements of income to their respective line items when these costs are incurred. Royalty payments to AbbVie on sales of IMRALDI are recognized in cost of sales within our condensed consolidated statements of income.

We share 50.0% of the profit or loss related to our 2013 commercial agreement with Samsung Bioepis, which is recognized in collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income. For the three and six months ended June 30, 2026, we recognized net profit-sharing expense of approximately $44.9 million and $102.1 million, respectively, to reflect Samsung Bioepis' 50.0% sharing of the net collaboration profits, compared to net profit-sharing expense of approximately $57.2 million and $105.2 million, respectively, in the prior year comparative periods.

Simultaneous with the formation of Samsung Bioepis, we also entered into a license agreement with Samsung Bioepis. Under this license agreement, we granted Samsung Bioepis an exclusive license to use, develop, manufacture and commercialize biosimilar products created by Samsung Bioepis using Biogen product-specific technology. In exchange, we receive single-digit royalties on biosimilar products developed and commercialized by Samsung Bioepis. Royalty revenue under the license agreement is recognized as a component of contract manufacturing, royalty and other revenue in our condensed consolidated statements of income.

Amounts receivable from Samsung Bioepis related to the agreements discussed above were approximately $3.5 million and $4.4 million as of June 30, 2026 and December 31, 2025, respectively. Amounts payable to

For additional information on our collaboration arrangements with Samsung Bioepis and our other significant collaboration arrangements, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in our 2025 Form 10-K.

As part of our acquisition of Apellis, we have a collaboration and license agreement with Sobi to jointly develop and commercialize pegcetacoplan for use systemically or for local non-ophthalmological administration. Under the agreement, we have commercialization rights for EMPAVELI in the U.S. and Sobi has exclusive rights to commercialize pegcetacoplan as ASPAVELI in the rest of the world.

Pursuant to the terms of our collaboration and license arrangement, as amended by a buy-down agreement entered into in July 2025 which reduces Sobi's royalty obligations by 90% subject to a defined cap, we are eligible to receive tiered royalties in the low single digits on net sales of ASPAVELI outside of the United States. If the defined cap is exceeded in a future period, the royalty terms in the original agreement will be reinstated, and we will earn royalties ranging from the high teens to high twenties on such net sales.

For the three and six months ended June 30, 2026, we recognized approximately $13.3 million in revenues from Sobi related to the agreements above, which are reflected as a component of contract manufacturing, royalty and other revenue in our condensed consolidated statements of income.

These arrangements may include the potential for future milestone payments based on the achievement of certain clinical and commercial development payable over a period of several years.

In March 2026 we entered into an exclusive license agreement with Alteogen Inc. to enable the development of a subcutaneous formulation of two biologics using Alteogen's ALT-B4 hyaluronidase technology.

In connection with the closing of this transaction we accrued an upfront payment of $20.0 million to Alteogen, which was recognized in acquired in-process research and development, upfront and milestone expense within our condensed consolidated statements of income for the six months ended June 30, 2026 and was paid during the second quarter of 2026.

Alteogen will also be eligible to receive a $10.0 million option payment if a second program is selected for development, as well as potential development, regulatory and commercial milestone payments and tiered royalties in the mid-single digit percentages on net sales of any combination products resulting from the collaboration.

In March 2026 we entered into a collaboration and license agreement with Alloy Therapeutics Inc. for the use of Alloy’s novel and proprietary AntiClastic ASO Platform. Through this collaboration, we plan to apply the platform to advance antisense therapeutics against multiple targets.

In connection with the closing of this transaction we accrued an upfront payment of $12.0 million to Alloy, which was recognized in acquired in-process research and development, upfront and milestone expense within our condensed consolidated statements of income for the six months ended June 30, 2026 and was paid during the second quarter of 2026.

In February 2025 we entered into a funding agreement with Royalty Pharma under which we received $200.0 million in 2025 and $50.0 million in 2026 to co-fund our development costs for the litifilimab program. As there is a substantive transfer of risk to the financial partner for the amount invested, the development funding will be

recognized by us as an obligation to perform contractual services. This funding was recognized as a reduction to research and development expense within our condensed consolidated statements of income, proportionate to the related expense. For the three and six months ended June 30, 2026, we received $25.0 million and $50.0 million, respectively, from Royalty Pharma, compared to $50.0 million and $100.0 million, respectively, in the prior year comparative periods. All funding has been received and the funding period has concluded as of June 30, 2026.

If the litifilimab clinical trials are successful for the indications based on the applicable clinical trials, upon regulatory approval in the U.S. or certain major markets in the world, Royalty Pharma will be eligible to receive approval-based fixed milestone payments of up to $250.0 million. The milestone payments due upon approval will be recorded as a component of other (income) expense, net within our condensed consolidated statements of income, when incurred.

If litifilimab receives regulatory approval, Royalty Pharma will be eligible to receive royalties of a mid-single digit percentage of the applicable net sales, which will be recorded as cost of sales within our condensed consolidated statements of income.

As part of our acquisition of HI-Bio in July 2024, we acquired HI-Bio's pre-existing in-license commitments under third-party agreements with MorphoSys (a wholly-owned subsidiary of Novartis), which included tiered royalties on potential future net sales ranging from high-single digit to mid-teen percentages, as well as potential development, regulatory and commercial milestone payments of up to $130.0 million, $230.0 million and $640.0 million, respectively. These amounts included milestone payments due upon the first patient dosed in a Phase 3 clinical trial of felzartamab in a first and second indication of $35.0 million and $30.0 million, respectively, which were earned during the first and second quarters of 2025 and recorded within acquired in-process research and development, upfront and milestone expense.

In April 2026 we entered into a definitive agreement with TJ Bio, where we assumed regulatory and sales milestone obligations under a pre-existing agreement between TJ Bio and MorphoSys and may pay MorphoSys tiered royalties on potential net sales of felzartamab in the greater China region.