Claude Code uses Bun written in Rust now
- ID
- 5916
- Status
- summarized
- Published
- 19 Jul 2026, 11:54 AM
- Fetched
- 20 Jul 2026, 12:04 PM
- Provider
- Simon Willison
- Category
- developer-ai
- Original URL
- https://simonwillison.net/2026/Jul/19/claude-code-in-bun-in-rust/
- Source URL
- https://simonwillison.net/atom/everything/
Summary
- Score
- 7.5
- Created
- 20 Jul 2026, 12:04 PM
- Tags
- Audience
- developersvibe_codersai_agent_users
What happened
Simon Willison verified that Claude Code v2.1.181 and later ship with a Rust port of Bun, finding 563 Rust source files embedded in the binary and a Bun version (1.4.0) not yet in public release. Jarred Sumner noted startup got 10% faster on Linux with otherwise minimal noticeable change, calling the quiet production rollout 'boring is good.'
Why it matters
For developers and AI agent users in Malaysia running Claude Code locally, this means faster startup and a more stable runtime under the hood without any config changes. It also signals that major AI tooling is increasingly betting on Rust for performance-critical runtimes, which is relevant for anyone building CLI tools or agents that need to ship fast and reliably.
Discussion angle
What it means for the local dev ecosystem when flagship AI tools quietly swap their runtime to Rust — should Malaysian builders building CLI agents or devtools also default to Rust or Bun over Node?