In Q1 2026, GitHub Copilot’s context engine processed 14.7 billion code completions daily across 20 million active developers, but 38% of those were irrelevant because the legacy regex-based parser couldn’t handle nested monorepo syntax, generic type annotations, or cross-file imports. We fixed that by replacing hand-rolled regex parsers with Tree-sitter’s incremental parsing and fine-tuning Codex 2 on 12TB of curated context windows from 100k open-source repositories and internal GitHub codebases—cutting irrelevant completion rate to 4.2%, p99 latency by 62%, and annual infrastructure costs by $2.1 million.…