Microsoft is testing DeepSeek V4 as a backend model for Copilot, marking the first time an open-source LLM is being considered for the core of Microsoft's flagship office product. The test is in a limited beta with enterprise customers.
The technical details: DeepSeek V4 is being tested as a "specialist" model within Copilot — handling specific tasks like code generation (Copilot for code) and data analysis (Copilot for Excel). Microsoft is not replacing the GPT-5.x backend entirely, but is using DeepSeek V4 for tasks where it shows a quality or cost advantage.
The "office software core" signal: Copilot is the core of Microsoft's AI strategy — it sits at the intersection of Office 365, GitHub, and Azure. Letting an open-source model into the Copilot stack is a significant strategic shift. The implication: Microsoft is signaling that "the best model wins" — even if it's open-source and Chinese.
The strategic angle: the move is also a hedge against OpenAI dependency. Microsoft has invested $13B in OpenAI, but the relationship has been strained (OpenAI's restructuring, the for-profit transition). Adding DeepSeek V4 to the Copilot stack gives Microsoft more leverage in the OpenAI relationship.
The bigger takeaway: "open-source LLM in core enterprise software" is no longer a hypothetical. DeepSeek V4 in Copilot is a real-world deployment, and it sets a precedent for other enterprises. For the industry, this means "open-source LLM as a primary model" is becoming a viable strategy for even the most conservative enterprises.