GitHub Copilot SDK (Technical Preview in 2026) is an official multi-platform toolkit from GitHub that lets developers embed the powerful Copilot agent runtime—planning, tool calling, file edits, code generation—directly into custom apps, services, CLIs, or bots. It powers the same engine as Copilot CLI, supports Node.js, Python, Go, .NET (with community extensions for others), BYOK for external LLMs, and customizable tools/skills. Ideal for building agentic experiences in your own products—programmatic access without reinventing orchestration. Requires Copilot subscription; pay-per-use via requests.