3Simon Willison's Weblog·
Claude Code now uses a Bun runtime written in Rust
Simon Willison notes that Claude Code has switched to using Bun (a JavaScript runtime) implemented in Rust as part of its execution stack. The post is brief but signals an infrastructure change in Anthropic's Claude Code agentic coding tool. This is relevant for practitioners tracking the internals and performance characteristics of Claude Code.
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Claude Code runtime migrated to Bun (written in Rust)
A Simon Willison post (surfaced via Hacker News with 173 points and 229 comments) notes that Anthropic's Claude Code agentic coding tool now uses Bun as its JavaScript runtime, which is itself implemented in Zig/Rust. The change is an infrastructure/tooling detail about the Claude Code execution environment. Community engagement suggests this is a notable implementation detail for practitioners using or building on Claude Code.
Anthropic Acquires Bun JavaScript Runtime as Claude Code Hits $1B ARR
Anthropic has acquired Bun, the high-performance JavaScript runtime and all-in-one toolchain founded by Jarred Sumner in 2021, to accelerate Claude Code's infrastructure. Claude Code reached $1 billion in annualized run-rate revenue in November 2025, just six months after its May 2025 general availability launch. The acquisition deepens an existing partnership—Bun was already integral to Claude Code's infrastructure scaling and its native installer launch. Bun will remain open source and MIT-licensed, with Anthropic committing continued investment in the project.
Claude 3.7 Sonnet and Claude Code: Anthropic's First Hybrid Reasoning Model and Agentic Coding Tool
Anthropic has released Claude 3.7 Sonnet, described as their most capable model to date and the first hybrid reasoning model on the market, capable of operating in both standard and extended thinking modes within a single unified model. The model achieves state-of-the-art results on SWE-bench Verified and TAU-bench, with particular strength in coding and front-end web development. Alongside the model, Anthropic is launching Claude Code in limited research preview, a command-line agentic coding tool that can read/edit files, run tests, and push to GitHub. Pricing remains unchanged at $3/M input and $15/M output tokens, with availability across Claude.ai plans, Amazon Bedrock, and Google Cloud Vertex AI.
Using Claude Code: The Unreasonable Effectiveness of HTML
Simon Willison shares commentary on using Claude Code, Anthropic's agentic coding tool, with a focus on HTML as an output format. The piece appears to explore practical workflows and observations from hands-on use of Claude Code. As a tier-2 practitioner commentary, it likely covers patterns, tips, or surprising findings about how Claude Code handles HTML generation or web-oriented tasks.
anthropics/claude-code: Agentic Terminal Coding Tool Trending on GitHub
Claude Code is an agentic coding tool developed by Anthropic that operates in the terminal, enabling natural language interaction with codebases for tasks like code execution, explanation, and git workflow management. The repository has accumulated 127,316 stars with 323 added today, indicating sustained community interest. It represents Anthropic's direct entry into the developer tooling space with an agent-oriented product.
Claude Code 2.1.208 release: accessibility, background agents, memory fixes, and performance improvements
Anthropic released Claude Code version 2.1.208, a substantial patch addressing dozens of bugs and adding several new features. Key additions include screen reader accessibility mode, vim insert-mode remapping, and a corporate process wrapper for enterprise deployments. The release fixes significant issues including memory leaks in long sessions, background agent reliability problems, streaming output truncation, and multi-second per-turn slowdowns from permission rule matching, alongside performance improvements yielding up to 7x faster tool rounds at high MCP tool counts.
Claude 3.5 Sonnet begins rollout on GitHub Copilot via Amazon Bedrock
Anthropic's Claude 3.5 Sonnet is now rolling out on GitHub Copilot, available in public preview for all Copilot Chat users in Visual Studio Code and GitHub.com. The model claims top performance on SWE-bench Verified among publicly available models and 93.7% on HumanEval. The integration runs via Amazon Bedrock's cross-region inference and reaches GitHub's community of over 100 million developers, representing a significant distribution milestone for Claude.
Anthropic Releases Claude Sonnet 4.5: Top Coding and Computer-Use Model with Agent SDK
Anthropic has released Claude Sonnet 4.5, claiming it is the best coding model and strongest model for building complex agents, with a 61.4% score on OSWorld (up from 42.2% for Sonnet 4) and state-of-the-art performance on SWE-bench Verified. The release is accompanied by major product upgrades including checkpoints in Claude Code, a native VS Code extension, a Claude Agent SDK giving developers access to the same infrastructure powering Claude Code, and new context editing and memory tools in the Claude API. Pricing is unchanged from Sonnet 4 at $3/$15 per million input/output tokens. Early enterprise customers including Cursor, GitHub Copilot, Devin, Canva, and Figma report significant gains in coding, agentic, and long-context tasks.