Clerk

Clerk provides drop-in authentication, user management, and authorization infrastructure for application developers, packaged as pre-built UI components and SDKs rather than a bare API that teams have to build a login screen around. For engineering teams, that means shipping sign-up, sign-in, session management, multi-factor authentication, organization/team management, and billing-adjacent user flows without building and maintaining that identity plumbing themselves — a category often called CIAM (customer identity and access management) when aimed at developers building their own products rather than internal workforce tools.

Founded in 2019 by Braden Sidoti and Colin Sidoti and headquartered in San Francisco, Clerk has raised a reported $134.3 million across multiple rounds, including a $30 million Series B backed by CRV and Stripe in January 2024 and a $50 million Series C in 2025 backed by Menlo Ventures and Anthropic’s Anthology Fund. According to the company, its platform now manages authentication for more than 200 million end users across roughly 15,000 applications, positioning it as a serious alternative to incumbents like Auth0 (now part of Okta) and Firebase Authentication in the developer-facing identity space.

Clerk’s Series C backing from Anthropic’s Anthology Fund signals a specific strategic bet: as AI agents increasingly need their own authenticated identities and permission scopes to act on behalf of users, Clerk is positioning its infrastructure to handle agent identity and authorization alongside traditional human end-user authentication. The company’s funding rounds and headline user/application counts are independently reported through venture press coverage, though the underlying usage figures ultimately originate from Clerk itself rather than an audited, third-party source.