<SEC-DOCUMENT>0000763212-25-000007.txt : 20251113
<SEC-HEADER>0000763212-25-000007.hdr.sgml : 20251113
<ACCEPTANCE-DATETIME>20251113202822
ACCESSION NUMBER:		0000763212-25-000007
CONFORMED SUBMISSION TYPE:	SCHEDULE 13G/A
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20251113
DATE AS OF CHANGE:		20251113

SUBJECT COMPANY:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			BIOGEN INC.
		CENTRAL INDEX KEY:			0000875045
		STANDARD INDUSTRIAL CLASSIFICATION:	BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
		ORGANIZATION NAME:           	03 Life Sciences
		EIN:				330112644
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-42028
		FILM NUMBER:		251480596

	BUSINESS ADDRESS:	
		STREET 1:		225 BINNEY STREET
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02142
		BUSINESS PHONE:		7814642000

	MAIL ADDRESS:	
		STREET 1:		225 BINNEY STREET
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02142

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	BIOGEN IDEC INC.
		DATE OF NAME CHANGE:	20070427

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	BIOGEN IDEC INC
		DATE OF NAME CHANGE:	20031112

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	IDEC PHARMACEUTICALS CORP / DE
		DATE OF NAME CHANGE:	19970530

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			PRIMECAP MANAGEMENT CO/CA/
		CENTRAL INDEX KEY:			0000763212
		ORGANIZATION NAME:           	
		EIN:				953868081

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G/A

	BUSINESS ADDRESS:	
		STREET 1:		177 EAST COLORADO BLVD.
		STREET 2:		11TH FLOOR
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91105
		BUSINESS PHONE:		6263049222

	MAIL ADDRESS:	
		STREET 1:		177 EAST COLORADO BLVD.
		STREET 2:		11TH FLOOR
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91105
</SEC-HEADER>
<DOCUMENT>
<TYPE>SCHEDULE 13G/A
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
<XML>
<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/schedule13g" xmlns:ns1="http://www.sec.gov/edgar/common">
  <headerData>
    <submissionType>SCHEDULE 13G/A</submissionType>
    <previousAccessionNumber>0001104659-03-028329</previousAccessionNumber>
    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0000763212</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
      </filer>
      <liveTestFlag>LIVE</liveTestFlag>



    </filerInfo>
  </headerData>
  <formData>
    <coverPageHeader>
      <amendmentNo>27</amendmentNo>
      <securitiesClassTitle>COM</securitiesClassTitle>
      <eventDateRequiresFilingThisStatement>09/30/2025</eventDateRequiresFilingThisStatement>
      <issuerInfo>
        <issuerCik>0000875045</issuerCik>
        <issuerName>Biogen Inc.</issuerName>
        <issuerCusip>09062X103</issuerCusip>
        <issuerPrincipalExecutiveOfficeAddress>
          <ns1:street1>225 Binney Street</ns1:street1>
          <ns1:city>Cambridge</ns1:city>
          <ns1:stateOrCountry>MA</ns1:stateOrCountry>
          <ns1:zipCode>02142</ns1:zipCode>
        </issuerPrincipalExecutiveOfficeAddress>
      </issuerInfo>
      <designateRulesPursuantThisScheduleFiled>
        <designateRulePursuantThisScheduleFiled>Rule 13d-1(b)</designateRulePursuantThisScheduleFiled>
      </designateRulesPursuantThisScheduleFiled>
    </coverPageHeader>
    <coverPageHeaderReportingPersonDetails>


      <reportingPersonName>PRIMECAP MANAGEMENT CO/CA/</reportingPersonName>
      <citizenshipOrOrganization>X1</citizenshipOrOrganization>
      <reportingPersonBeneficiallyOwnedNumberOfShares>
        <soleVotingPower>14859187</soleVotingPower>
        <sharedVotingPower>0</sharedVotingPower>
        <soleDispositivePower>14954697</soleDispositivePower>
        <sharedDispositivePower>0</sharedDispositivePower>
      </reportingPersonBeneficiallyOwnedNumberOfShares>
      <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>14954697</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>
      <aggregateAmountExcludesCertainSharesFlag>N</aggregateAmountExcludesCertainSharesFlag>
      <classPercent>10.2</classPercent>
      <typeOfReportingPerson>IA</typeOfReportingPerson>
    </coverPageHeaderReportingPersonDetails>
    <items>
      <item1>
        <issuerName>Biogen Inc.</issuerName>
        <issuerPrincipalExecutiveOfficeAddress>225 Binney Street, Cambridge, MASSACHUSETTS
02142</issuerPrincipalExecutiveOfficeAddress>
      </item1>
      <item2>
        <filingPersonName>PRIMECAP MANAGEMENT CO/CA/</filingPersonName>
        <principalBusinessOfficeOrResidenceAddress>177 EAST COLORADO BLVD.
11TH FLOOR
PASADENA, California
91105</principalBusinessOfficeOrResidenceAddress>
        <citizenship>PRIMECAP MANAGEMENT CO/CA/ - UNITED STATES</citizenship>
      </item2>
      <item3>
        <notApplicableFlag>N</notApplicableFlag>
        <typeOfPersonFiling>IA</typeOfPersonFiling>
      </item3>
      <item4>
        <amountBeneficiallyOwned>14,954,697</amountBeneficiallyOwned>
        <classPercent>10.2</classPercent>
        <numberOfSharesPersonHas>
          <solePowerOrDirectToVote>PRIMECAP MANAGEMENT CO/CA/ - 14,859,187</solePowerOrDirectToVote>
          <sharedPowerOrDirectToVote>PRIMECAP MANAGEMENT CO/CA/ - 0</sharedPowerOrDirectToVote>
          <solePowerOrDirectToDispose>PRIMECAP MANAGEMENT CO/CA/ - 14,954,697</solePowerOrDirectToDispose>
          <sharedPowerOrDirectToDispose>PRIMECAP MANAGEMENT CO/CA/ - 0</sharedPowerOrDirectToDispose>
        </numberOfSharesPersonHas>
      </item4>
      <item5>
        <notApplicableFlag>Y</notApplicableFlag>
      </item5>
      <item6>
        <notApplicableFlag>N</notApplicableFlag>
        <ownershipMoreThan5PercentOnBehalfOfAnotherPerson>Various Persons have the right to receive, or the power to direct the receipt of, dividends from, or proceeds from the sale of, with respect to the securities as to which this Schedule is filed. No one Person here has an interest more than five percent of this class of securities except as follows: Vanguard PRIMECAP Fund has an interest of more than five percent of the total outstanding common stock of Biogen Inc.</ownershipMoreThan5PercentOnBehalfOfAnotherPerson>
      </item6>
      <item7>
        <notApplicableFlag>Y</notApplicableFlag>
      </item7>
      <item8>
        <notApplicableFlag>Y</notApplicableFlag>
      </item8>
      <item9>
        <notApplicableFlag>Y</notApplicableFlag>
      </item9>
      <item10>
        <notApplicableFlag>N</notApplicableFlag>
        <certifications>By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.</certifications>
      </item10>
    </items>
    <signatureInformation>
      <reportingPersonName>PRIMECAP MANAGEMENT CO/CA/</reportingPersonName>
      <signatureDetails>
        <signature>Jorge A. Rodriguez</signature>
        <title>Deputy Chief Compliance Officer</title>
        <date>11/13/2025</date>
      </signatureDetails>
    </signatureInformation>
  </formData>
</edgarSubmission>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
