Is Your Agent an App? What MCP and the ChatGPT Apps SDK Mean for Portability

Subtitle: The "model is the OS, agents are the apps" idea is useful for builders only if your agent can actually move. Here is what to check.

By Tej Pandya, founder of GrowEasy.ai

The comparison between AI models and operating systems is popular, and Andrej Karpathy used it in 2023. As a builder, I care about one practical part of it: does an "agent app" run on one platform, or on many?

MCP connects apps to tools, but does not guarantee portability

OpenAI's Apps SDK, which it describes as available in preview, lets you design the logic and interface of an app that runs inside ChatGPT. It is built on the Model Context Protocol (MCP), which OpenAI calls an open standard. Its Help Center says apps built with the SDK can run anywhere that adopts the standard. In December 2025 Anthropic donated MCP to the Agentic AI Foundation under the Linux Foundation, co-founded with Block and OpenAI.

That December post also said MCP was adopted by ChatGPT, Cursor, Gemini, Microsoft Copilot and Visual Studio Code. I am quoting a December 2025 statement, not a current count.

Test storage, tools and behaviour on a second platform

• Keep tool definitions in MCP servers, not in prompts tied to one product.
• Keep state and user data in your own storage, so you can leave.
• Treat the UI layer as the part most likely to be platform specific.
• Test the same agent on a second model before you promise it works on both. Behaviour changes with the model, the prompt and the tools.

Treat the app-platform analogy as a direction, not adoption proof

I found no numbers for how many people use third-party apps inside agent platforms. Treat "agents are the new apps" as a direction. Windows is also adding agent controls (identity, isolation, policy), so the old OS is not standing still.

Sources: https://help.openai.com/en/articles/12515353-build-with-the-apps-sdk , https://www.anthropic.com/news/donating-the-model-context-protocol-and-establishing-of-the-agentic-ai-foundation , https://developer.microsoft.com/en-us/windows/agentic , https://arxiv.org/abs/2312.03815