Bun: A Slow Hot Reload in a Browser Game Led Jarred Sumner to Build a New JavaScript Runtime in a Cramped Oakland Apartment, and Then to Anthropic
Jarred Sumner started Bun in 2021 because a voxel game he was building took 45 seconds to reload. After more than a year of solo work in Zig, Bun v0.1.0 launched in July 2022 and reached 20,000 GitHub stars in its first week. His company Oven raised a $7 million seed led by Kleiner Perkins and a $19 million Series A led by Khosla Ventures, shipped Bun 1.0 in September 2023, and in December 2025, with zero revenue but over four years of runway, joined Anthropic, where Bun powers Claude Code.
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