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GitHub Copilot CLI Speeds Up C++ Code Intelligence with Whole Codebase Indexing

GitHub CopilotView original changelog

GitHub Copilot CLI now builds a persistent whole codebase index (WCI) for C++ projects, letting the Microsoft C++ Language Server resolve types, symbols, includes, and cross-file relationships from a reusable index instead of rediscovering them on every request. Enabled by default as of September 22, 2026, it speeds up definitions, references, implementations, and symbol search, especially in large, multi-million-line C++ codebases. Developers can monitor indexing progress with /lsp logs and disable WCI if the initial index build's memory overhead is a concern.

Key Takeaways

  • Whole codebase indexing (WCI) gives GitHub Copilot CLI a persistent, reusable symbol index for C++ projects instead of rediscovering project structure on every request.
  • The Microsoft C++ Language Server powers the index, resolving types, symbols, includes, and file relationships from the project's compilation information.
  • WCI is enabled by default, so most C++ developers using Copilot CLI get the speedup automatically without extra configuration.
  • The first index build can be slow and memory-intensive on large repositories, though subsequent lookups reuse the index and update incrementally.
  • Developers can track indexing progress with the /lsp logs command and disable WCI (with a session restart) if the tradeoff isn't worth it for their project.
  • The feature targets one of C++ development's classic pain points: million-line, multi-file codebases where naive code-intelligence tools struggle to stay fast.

Sources & Mentions

1 external resource covering this update

Faster C++ code intelligence with whole codebase indexing

daily.dev

Whole Codebase Indexing Speeds Up C++ NavigationGitHub Copilot CLI now supports whole codebase indexing (WCI) for C++ projects, addressing a common pain point for large native codebases: without a reusable index, every request for a definition, reference, or symbol search has to rediscover the relevant project details from scratch, and C++ projects routinely span millions of lines across deeply interconnected files.

How Whole Codebase Indexing WorksWCI builds a persistent index of symbols across an entire C++ project, including files that are not currently open. The underlying Microsoft C++ Language Server uses the project's compilation information to resolve types, symbols, includes, and the relationships between files, then reuses that resolved data instead of recomputing it on every Copilot request. The practical result is faster answers when Copilot needs to find definitions, references, implementations, or run a symbol search.

Enabled by Default, With Some Startup CostWhole codebase indexing is on by default. The language server builds the index when a C++ project first opens, and developers can check progress with the /lsp logs command. Building that first index can take extra time and temporarily use more memory on large or complex repositories, though the index persists and updates incrementally afterward rather than rebuilding from zero on every session. Developers who want to opt out can disable WCI and restart their Copilot session.

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