AI Code-Testing Startup Blacksmith Raises $45M Series B, Valuation Jumps 10x to $550M

ycombinator · x · 2026-08-12

Y Combinator W24 startup Blacksmith has raised a $45 million Series B round, bringing its valuation to $550 million—nearly a 10x increase from its $60 million valuation during its Series A less than a year ago.

As AI coding tools like Cursor and Claude Code make code generation dramatically easier, testing and validating that code has become the next major industry bottleneck. Blacksmith builds infrastructure to help companies build, test, and verify software before it reaches production.

The startup's customer base has surged from just over 700 to over 5,000, including clients like Supabase, Clerk, and Mercury. Notably, Blacksmith hit a $10 million ARR with only 10 employees, and its revenue has since grown to tens of millions.

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