Alnylam Pharmaceuticals (ALNY) Stock After Hours: What Happened After the Dec. 19, 2025 Close — and What to Watch Before the Next Market Open
Alnylam Pharmaceuticals (ALNY) closed Friday, Dec. 19, 2025, at $400.23, up 1.15% on heavy volume of 12.6 million shares, with little movement after hours. The Nasdaq-100 reconstitution takes effect before the U.S. market opens Monday, Dec. 22, adding Alnylam to the index. Friday’s session saw record derivatives expirations, amplifying trading volume.