Under the hoodTier: how much it should matter to you
2Useful: my rating, 1 to 5
3Signal: worth watching, 1 to 5
MCP AppsArea: what it touches
Internal ChangesKind: in v2.1.317,
Internal ChangesSection of the release
What
The SDK is the toolkit programs use to drive Claude Code. Its format for user messages gained an optional field, tool_states, which is marked as internal.
The field holds the states of MCP App views. These are views that MCP servers can show; MCP servers are outside programs that give Claude Code extra tools. The states come from a remote client, sent together with a prompt. When the field is present, it replaces the set of view states held by the process running the session.
Why
A remote client can pass the state of these views along with a prompt to the session that handles it.
