---
schema_version: "secwatch.filing_event.v1"
accession: "0001193125-25-117854"
form_type: "8-K"
ticker: "BIIB"
cik: "0000875045"
company_name: "BIOGEN INC."
filed_at: "2025-05-12T23:59:59+00:00"
generated_at: "2026-05-22T01:03:22.413557+00:00"
event_type: "debt"
sentiment: "neutral"
materiality_score: 0.55
calibrated_materiality_score: 0.55
confidence: "high"
source: SEC EDGAR
---

# Biogen issues $1.75B in three tranches of senior notes to refinance maturing 2025 debt

## Summary
- $400M 5.050% notes due 2031, $650M 5.750% notes due 2035, $700M 6.450% notes due 2055.
- Net proceeds, with cash on hand, will retire the outstanding $1.75B 4.050% Senior Notes due 2025.
- Notes are senior unsecured; redeemable at par plus make-whole; 101% change-of-control put.
- Underwriters: BofA Securities, Citigroup Global Markets, J.P. Morgan Securities.

## SEC filing metadata
- accession: 0001193125-25-117854
- form_type: 8-K
- ticker: BIIB
- cik: 0000875045
- company_name: BIOGEN INC.
- filed_at: 2025-05-12T23:59:59+00:00
- event_type: debt
- sentiment: neutral
- materiality_score: 0.55
- calibrated_materiality_score: 0.55
- confidence: high
- sec_items: 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/875045/000119312525117854/0001193125-25-117854-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/875045/000119312525117854/d13940d8k.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001193125-25-117854
- JSON: https://secwatch.observer/filing/0001193125-25-117854.json
- Plain text: https://secwatch.observer/filing/0001193125-25-117854.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.