Host capability matrix

Every host implements a subset. An API that exists in ChatGPT may be undefined in M365 Copilot and absent in a custom host. Unsupported APIs are undefined, not throwing — so a missing guard produces a silent dead button, not an error you will notice in testing.

The tables below are the published Microsoft 365 Copilot support matrix, which is the most complete public statement of any host's coverage. Treat ChatGPT as full support for the window.openai column (it defines it) and Claude as full support for the MCP Apps column. Verify at runtime regardless.

Component bridge