Microsoft made OpenAI’s deep reasoning O1 model available free to all Copilot users in July 2026, removing paywalls around reasoning-class AI models. Copilot Chat now includes GPT 5.5 Thinking, a model designed for multistep reasoning and structured analysis, allowing users to follow the chain-of-thought. Copilot in SharePoint now runs on the latest reasoning OpenAI model for everyone without a fallback to lighter models. Microsoft 365 Copilot declarative agents now default to GPT-5.1 with automatic model selection. The timing of making O1 free comes as DeepSeek’s reasoning models generate buzz in the market.