This market resolves YES if, by 2026-12-31 23:59 PT, an official Microsoft source says that Microsoft Excel's Agent Mode, Copilot in Excel, or a direct renamed successor inside Excel supports selecting Google Gemini or a Gemini-family model to create, edit, analyze, or reason over workbooks. Qualifying official sources include Microsoft Support, the Microsoft 365 Blog, Microsoft Tech Community posts by Microsoft staff, Microsoft release notes, or Microsoft 365 admin/message-center documentation that is publicly visible or verifiably quoted. A public preview, Frontier feature, staged rollout, or commercial-only tenant feature counts if Microsoft says Gemini is selectable in Excel's agentic/Copilot workflow by the deadline. Resolves NO if Excel's agentic/Copilot workflow still only supports Microsoft/OpenAI/Anthropic models, or if Gemini support exists only in Google Workspace, third-party Excel add-ins, Copilot Studio agents outside Excel, generic Microsoft 365 Copilot chat outside Excel, leaks, rumors, or unaffiliated wrappers. A plan to add Gemini after the deadline is not enough unless Microsoft says support is available or rolling out by the deadline. Creation source check: Microsoft Support currently says Agent Mode in Excel uses the latest OpenAI models by default and lets subscribers switch to the latest Anthropic models using the model picker; a separate Microsoft Support page says Agent Mode in Excel supports Claude models. I found no official Microsoft source saying Gemini is selectable in Excel Agent Mode at creation. Sources: - Agent Mode in Excel: https://support.microsoft.com/en-au/office/agent-mode-in-excel-frontier-a2fd6fe4-97ac-416b-b89a-22f4d1357c7a - Use Claude with Agent Mode in Excel: https://support.microsoft.com/en-us/topic/use-claude-with-agent-mode-frontier-in-excel-b2c3b3ec-154b-484b-84d0-914a80df395a - Vibe working announcement: https://www.microsoft.com/en-us/microsoft-365/blog/2025/09/29/vibe-working-introducing-agent-mode-and-office-agent-in-microsoft-365-copilot/