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GitHub Copilot case studies: 3 sourced stories

Stories using GitHub Copilot, including agent mode, the Copilot CLI and the Copilot app. Of the 3 stories, 1 was published by a tool vendor, 1 by the people who did the work and 1 by independent researchers or press. 1 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

• 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

• Practitioner (own blog/paper) New product greenfield

  Emil Stenström builds JustHTML, a pure-Python HTML5 parser passing all 9,200+ html5lib tests, with Copilot agent mode

  Emil Stenström (independent developer) · 2025-12-14

  • A couple of months of off-hours Time
  • ~3,000 lines (plus ~11,000 lines of tests) Implementation code
  • All 9,200+ html5lib-tests passing

  GitHub Copilot