a16z Launches Cosign, Turning Endorsements Into a Career Reputation Layer

On September 25, a16z launched Cosign, a curated endorsement network for the startup ecosystem positioned as its "reputation layer." It is led by Erik Torenberg together with Josh Elman, Olivia Moore and David Booth, and aims to formalize how trust circulates in Silicon Valley.

Confirmed

• Core idea: the most valuable signal in Silicon Valley is not credentials but "who is willing to vouch for you," summed up by the slogan "If you believe in someone early, say so"
• The product is an invitation-style professional network building a verifiable endorsement graph: who you have actually worked with and who would work with you again, turning fleeting recommendations on X into permanent records
• It includes a startup directory listing investors and founders
• A repost cites PG's 2009 endorsement of Sam Altman as a historical example of endorsement value
• David Hoang says he will write about whisper networks and argues Cosign can turn personal credibility into accumulable capital — for referrals, amplifying important work, recognizing potential, or vouching for founders

Why it matters

• Reputation today moves informally (private referrals, retweets); Cosign attempts to structure it as a queryable, accumulable career asset, which if widely adopted could reshape talent and trust discovery in the startup world
• Backed by a16z and operated by well-known operators, it can leverage the trust chains of Silicon Valley's core network at cold start

2026-09-25 ~ 2026-09-26 · 5 related posts

• [source] a16z launches Cosign, a professional reputation product built on endorsements — a16z · 2026-09-25
• [source] a16z-backed Cosign launches as a durable reputation layer for the startup ecosystem — a16z · 2026-09-25
• [source] Erik Torenberg launches Cosign, a tool to turn co-signs and credibility into portable capital — davidhoang · 2026-09-26

2 near-duplicate retellings: a16z · omooretweets