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Language ports: 5 sourced coding agent stories

Moving a codebase from one programming language to another, such as Scala to Java or Zig to Rust. Of the 5 stories, 4 were published by a tool vendor and 1 by the people who did the work. 4 involve an existing codebase and 1 started from scratch. Every number links to where it was published.

• Vendor-published Language port brownfield

  GitHub ports the Copilot agent runtime from TypeScript to 800K+ lines of Rust, mostly by one engineer

  GitHub (Microsoft) · 2026-09-16

  • 832,378 lines Production Rust written
  • ~430,000 lines TypeScript passed through the port (author estimate)
  • ~14.5 weeks Porting window

  GitHub Copilot

• Vendor-published Language port brownfield

  Bun's 535,000-line Zig codebase is ported to Rust in 11 days by up to 64 parallel Claude Code agents

  Bun (Oven / Anthropic) · 2026-07-08

  • 535,496 lines of Zig (excluding comments), 1,448 .zig files Source size
  • 11 days (May 3 to merged May 14, 2026) Time
  • 6,778 Commits

  Claude Code

• Practitioner (own blog/paper) Language port greenfield

  Simon Willison ports an HTML5 parser from Python to JavaScript with Codex CLI in about 4.5 hours

  Simon Willison (independent developer) · 2025-12-15

  • ~4–4.5 hours Idea to finished library
  • 8 Prompts
  • 9,000 lines of JavaScript, 43 commits Output

  OpenAI Codex

• Vendor-published Language port brownfield

  Stripe migrates 10,000 lines of Scala to Java in four days

  Stripe

  • 10,000 Lines migrated
  • 4 days Actual duration
  • 10 engineering weeks Manual estimate

  Claude

• Vendor-published Language port brownfield

  Wiz ports a 50,000-line Python PDF library to Go in about 20 hours with Claude Code

  Wiz

  • ~50,000 lines of Python (pypdf) Source size
  • 18,413 lines of Go Output size
  • ~20 hours (10 active development, 10 testing) Time

  Claude Code