Microsoft Integrates GPT-5.5 Instant into 365 Copilot

Microsoft has integrated OpenAI's GPT-5.5 Instant model into Microsoft 365 Copilot and Copilot Studio, just two days after OpenAI released the model as the new default for ChatGPT users. This upgrade replaces the previous GPT-5.3 Instant model, which had been integrated into Microsoft 365 Copilot since March 2026. According to OpenAI, the new model produced 52.5% fewer hallucinated claims than its predecessor on high-stakes prompts in medicine, law, and finance, and saw a 37.3% reduction in inaccurate responses on conversations users had previously flagged for errors. ## What GPT-5.5 Instant Brings to Enterprise Users The GPT-5.5 Instant model features improved context handling, with the ability to reference past conversations and files to deliver more relevant answers. The model includes a 'smart-switching' capability that can trigger deeper reasoning when a prompt is particularly complex. This capability is designed to provide more accurate and relevant responses to user queries. ## Microsoft's Broader AI Integration Strategy The Microsoft 365 Copilot integration follows the company's earlier rollout of GPT-5.5's full reasoning model into its Copilot ecosystem in late April, which enhanced multi-step task execution across GitHub, Microsoft 365, and Azure Foundry. Users can select specific models or allow an auto mode to choose the most appropriate model for each request. The rapid two-day turnaround from OpenAI's consumer launch to Microsoft's enterprise deployment underscores the tight integration between the two companies as they compete with Google's Gemini across both consumer and enterprise AI markets. The GPT-5.5 Instant model is now available to all Microsoft 365 Copilot users, while the previous GPT-5.3 Instant model will remain available to paid subscribers for three months before being retired.