What
The SDK's dynamic MCP server management, used to add or change MCP (Model Context Protocol, a way to connect external tools) servers at runtime, now enforces new restrictions:
- A server pushed while a session is running must be an http server on that session's own MCP proxy route.
- Certain server names are reserved for first-party servers and can only be set when the session starts, not pushed later.
- Servers can only be turned on or off by replacing the entire server set at once, not by toggling one individually.
- A configuration change to a server that's already running is held and applied on the next re-dispatch, rather than immediately.
Why
These restrictions add guardrails around runtime MCP server management, preventing conflicts with built-in servers and making changes to a running server's configuration more predictable.