According to Ethan Mollick on Twitter, multiple attempts to have Claude build a fully playable game entirely within Excel worksheets failed, with one design making the model act as the game master and another nonfunctional layout, highlighting current LLM limits in tool-constrained, stateful system design (as reported by Ethan Mollick). According to Ethan Mollick, the tests show Claude’s difficulty with strict in-sheet logic, dependency tracking, and enforcing no external engine, underscoring the need for explicit spec checks, test harnesses, and verification when using LLMs for spreadsheet automation. As reported by Ethan Mollick, the business takeaway is that enterprises should pair LLMs with validation scripts, protected cell schemas, and deterministic formula libraries when deploying Excel-based copilots and games to reduce hallucinated control flows and ensure maintainability.