Plan Mode in Cursor enhances the performance of frontier models on long horizon tasks by emphasizing upfront planning and detailed specifications. It provides developers with tools to create and update plans using an interactive editor, which allows for comprehensive research into the codebase by reading files, reviewing documentation, and asking clarifying questions. Once an approach is aligned upon, Cursor generates a markdown plan with code snippets, file paths, and implementation details that can be collaboratively edited and saved in a repository for future reference. Plan Mode is accessible through a simple shortcut and encourages a collaborative process where developers refine implementation steps before proceeding to build directly from the plan, ultimately resulting in stronger research and a more directed approach to complex coding tasks.