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Claude Code case studies: 16 sourced stories

Stories where Anthropic's Claude Code agent did some or all of the work. Of the 16 stories, 4 were published by a tool vendor, 10 by the people who did the work and 2 by independent researchers or press. 4 involve an existing codebase and 9 started from scratch. Every number links to where it was published.

• Practitioner (own blog/paper) New product greenfield

  Three people build Loft with coding agents over three months, then ship its open format 53 hours after the first commit

  Loft · 2026-10-16

  • 3 people Team
  • ~3 months (July 10 – Oct 16) V1 duration
  • Nearly 2,000 (merges excluded) V1 commits

  Claude Code, OpenAI Codex

• Practitioner (own blog/paper) New product greenfield

  Foxbox Digital ships a production marketing site with two engineers in 14 days using Claude Code

  Foxbox Digital (agency) · 2026-10-14

  • 2 weeks Calendar time
  • 2 engineers Team
  • ~9,200 Lines of code

  Claude Code

• Practitioner (own blog/paper) New product greenfield

  Sparq builds a 22-agent internal platform with Claude Code: 34,000 lines across 453 commits

  Sparq · 2026-10-14

  • ~34,000 Python Lines of code
  • 453 / 159 Commits / PRs
  • 4 Repositories

  Claude Code

• Practitioner (own blog/paper) New product greenfield

  Token Clicker: a 33,716-line browser idle game shipped 19 hours after its specs with Claude Code

  Julien Renaux (independent developer) · 2026-09-28

  • 19 hours 39 minutes wall-clock (night included) Specs to launch
  • 33,716 lines TypeScript in src/
  • 1,758 unit, 34 pacing, 28 end-to-end Tests

  Claude Code

• Practitioner (own blog/paper) New product greenfield

  Solo developer builds a cross-platform tower defense game in about 30 days with Claude Code, for ~$2,755 in tokens

  Julien Renaux (independent developer) · 2026-09-10

  • ~30 days, ~12 working sessions Duration
  • 9,436 Tool calls
  • 17.7M Output tokens

  Claude Code

• Practitioner (own blog/paper) Refactor / maintenance greenfield

  An agent-written 150,000-line Rust app shows refactoring one 17,155-line file cut input tokens per change by 83%

  Giles Edwards-Alexander (writing on martinfowler.com) · 2026-07-30

  • ~150,000 lines (~120k Rust) App size
  • 17,155 lines Largest file before
  • 3,695 lines Largest file after

  Claude Code, Cursor

• 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

• Independent Company rollout

  Uber caps AI coding spend at $1,500 per employee per tool after burning its annual AI budget in 4 months

  Uber · 2026-06-02

  • $1,500 per employee, per tool Monthly cap
  • 4 months Time to exhaust annual AI budget

  Claude Code, Cursor

• Independent Research / benchmark

  NBER study of 500,000+ GitHub developers: coding agents multiply commits and code, but releases rise only ~20%

  NBER working paper (Demirer, Musolff, Yang) · 2026-05

  • 500,000+ Developers studied
  • +30% autocomplete, ~+180% with sync agents, ~+240% with async agents (cumulative) Weekly commits
  • +958% Sync agents: lines of code

  GitHub Copilot, Claude Code, OpenAI Codex

• Vendor-published New product greenfield

  16 parallel Claude agents build a 100,000-line Rust C compiler that builds Linux, for ~$20,000

  Anthropic (Nicholas Carlini) · 2026-02-05

  • Just under $20,000 API cost
  • ~2 weeks, nearly 2,000 Claude Code sessions Duration
  • 100,000-line compiler Output

  Claude Code

• Practitioner (own blog/paper) Migration brownfield

  Spotify's background coding agent merges 1,500+ migration PRs with 60–90% time savings

  Spotify · 2025-11

  • 1,500+ Agent PRs merged to production
  • 60–90% vs writing by hand Time saved on these migrations
  • Hundreds of developers Users

  Claude Code, Claude Agent SDK, Honk (Spotify)

• Practitioner (own blog/paper) Upgrade / modernisation brownfield

  Claude Code ports a 25-year-old Linux tape driver from kernel 2.4 to 6.8 over two evenings

  Dmitry Brant (independent developer) · 2025-09-07

  • Two evenings Time
  • 2.4 → 6.8 Kernel version jump
  • Probably several weeks (would have meant learning 25-year-old kernel development) Author's by-hand estimate

  Claude Code

• Practitioner (own blog/paper) New product greenfield

  Solo developer ships a 20,000-line native macOS app, writing fewer than 1,000 lines by hand

  Indragie Karunaratne (independent developer) · 2025-07-01

  • ~20,000 lines Codebase size
  • <1,000 lines (author's estimate) Written by hand
  • 2,000 lines of Python, written by Claude in a few hours of iteration Release automation script

  Claude Code

• Practitioner (own blog/paper) New product greenfield

  Cloudflare's Kenton Varda prompts an OAuth 2.1 provider library out of Claude Code in about five days

  Cloudflare · 2025-06-03

  • ~5 days of heavy work (with other duties), plus minor commits over the month Time with AI
  • ~5,000 lines incl. comments, tests and docs Library size
  • 2–5x longer ("a few weeks, maybe months") Author's by-hand estimate

  Claude Code

• Vendor-published Company rollout

  Stripe rolls Claude Code out to 1,370 engineers with a zero-configuration binary

  Stripe

  • 1,370 Engineers with Claude Code enabled
  • 2–3 months Time to produce signed enterprise binary
  • 6 Coding assistants enabled at Stripe

  Claude Code

• 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