Custom App (MCP) not working with GPT 5.4 pro, only with regular GPT 5.4
OpenAI Developer Community
April 6, 2026
Hi there, I’m trying to use an MCP in ChatGPT with GPT 5.4 pro, but it’s not working. I’ve found that the MCP works completely fine when I switch to instant. Any advice on how to fix this?
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