a16z launches Cosign, an endorsement-based professional network for startups
omooretweets · x · 2026-09-25
a16z has launched Cosign, a curated professional network for the startup community built by Erik Torenberg, David Booth, Josh Elman, and Olivia Moore.
What it does:
- Startup directory: investors, companies, and operators with their histories and collaborators
- Cosign graph: who shaped your career, who'd work with you again, who thinks you're one to watch
- Durable reputation: endorsements that would vanish into the feed get permanently attached to people and companies
- Discovery: e.g. best fintech angels, AI companies worth tracking
Backstory: seven years ago Torenberg emailed a few hundred people asking for one person to watch — the answer was Russell Kaplan, then a 22-year-old Tesla engineer, now president of Cognition. Paul Graham cosigned Sam Altman in 2009, six years before OpenAI existed. Olivia Moore's thesis: "the most valuable data in Silicon Valley is who has conviction in who."
Related event: a16z Launches Cosign, Turning Endorsements Into a Career Reputation Layer(5 posts)→
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