Anthropic’s October 26, 2026 S-1 filing, which formally designates Goldman Sachs in the lead-left underwriting position with Morgan Stanley as co-lead and stabilization agent, is the decisive catalyst anchoring the 88% market-implied probability for Goldman Sachs. This disclosure reversed earlier trader consensus favoring Morgan Stanley and aligns with the bank’s prior lead-left role on SpaceX’s June IPO, where it earned top fees within a 22-bank syndicate. The filing also highlights Anthropic’s rapid revenue expansion to $16.3 billion in the first half of 2026 and its planned Nasdaq listing under ticker ANT, potentially the largest IPO on record at up to $100 billion. Other banks, including JPMorgan at 0.6%, remain sidelined as the prospectus order establishes clear hierarchy.