Use Copilot for in-editor, repo-tied snippets and quick ADR edits—fast and code-aware but limited to file/PR context and not built for formal citations. Use ChatGPT for long-form architecture docs and decision records: larger context windows, better structuring/summarization, and can include cited sources when you feed retrieval results. Practical flow: draft and synthesize in ChatGPT, then use Copilot to inject code examples and local edits.

Compare ChatGPT capabilities: Compare ChatGPT and Gemini