Perform Repository-Wide Migrations in a Single Day
Execute massive codebase migrations in 24 hours using 1M context.
Leverage the 1-million token context window of Claude Fable 5 to perform holistic, repository-wide migrations and refactors that previously required team-wide coordination. 🏗️
The Scenario
Your company needs to migrate a massive legacy codebase (like a large Ruby or Java app) to a modern framework, a task usually reserved for an entire engineering team for several months.
Before & after
A team of developers would manually refactor code block by block, requiring extensive regression testing and coordination over 2–3 months.
Input the entire 1M token context into Claude Fable 5 and ask it to execute the migration across the whole set. The model can process the entire migration in roughly 24 hours of background processing or iterative prompts.
The Prompt
I am providing a large segment of my codebase. I need to migrate this entire library from [OLD_LANGUAGE/FRAMEWORK] to [NEW_LANGUAGE/FRAMEWORK]. Please analyze the global dependencies first, then provide a step-by-step migration plan and the refactored code for the primary modules. [PASTE_CODE_OR_UPLOAD_PROJECT]
Fable 5 supports a 1-million token context window, which is large enough to hold massive codebases (e.g., 50 million lines of code in segments or entire documentation libraries). This allows for 'codebase-wide' actions rather than file-by-file edits.
Source
Claude Platform - Claude API Docs"Fable 5 performed a codebase-wide migration in a day that would otherwise have taken a full team more than two [months]."