What
MCP (Model Context Protocol) servers give Claude extra tools. Their results can carry extra details in a field called _meta.
- The
_metaon a tool result is now built by a shared helper instead of copying a single flag. - Stripping
_metafrom text blocks never worked because the code checked the wrong value. That is fixed. - If the text blocks'
_metais over a character limit, or cannot be turned into JSON, it is left off the kept result. - When reading a request id, ids starting with
late-bind-are now ignored.
Why
Large _meta from an MCP server no longer bloats the results Claude Code keeps, and requests are matched up differently when they use late-bind ids.
Names in the bundle_meta
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Added since
A small documentation edit on Completion touched a line naming _meta after this was published.
> [`_meta`](https://modelcontextprotocol.io/specification/2026-07-28/basic/index#meta).specification/2026-07-28/server/utilities/completion see the edit
Confirmed since
Anthropic's documentation has since written up _meta, on Configure permissions.
Tools that require user interaction behave the same way: `AskUserQuestion` and MCP tools whose server sets [`_meta["anthropic/requiresUserInteraction"]`](/docs/en/mcp#require-approval-for-a-specific-tool) always fall through to the callbac…agent-sdk/permissions see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up _meta, on Configure permissions.