Bun is Great Software, but Anthropic Acquisition Raises Concerns

Anthropic acquired the JavaScript runtime Bun in December 2025, promising to keep it open source and MIT‑licensed while the same team continued development. The acquisition was highlighted by the fact that Claude Code ships as a Bun executable, meaning any instability in Bun would directly affect Claude Code’s reliability. In April 2026, users began reporting a decline in Claude Code quality, including reduced default reasoning effort, a stale‑session bug, and a prompt change that hurt coding quality. Anthropic’s engineering post‑mortem blamed product‑layer issues and noted that OpenClaw billing changes and third‑party harness restrictions were contributing factors. The article also reports that a commit mentioning OpenClaw in a JSON blob could trigger billing surprises or request refusals, even in empty repositories. Despite these issues, the Bun team remains active, and Anthropic has the resources to maintain performance and stability. However, the integration of Bun into Anthropic’s product stack has raised concerns about potential policy changes that could affect Bun’s open‑source nature. Developers using Bun for production workloads are advised to monitor for any changes in licensing or feature deprecation that may arise from Anthropic’s ownership.