What probably matters to youSection of the release
What
There is a new command-line flag, --client-data-url <url>, and a matching environment variable, CLAUDE_CODE_CLIENT_DATA_URL. Setting the variable instead of the flag keeps the URL out of the process list. The URL points to a signed configuration document on downloads.claude.ai. At startup Claude Code downloads the document, checks its signature, and applies the part that matches the model the session uses.
Claude Code will not start when:
the document cannot be loaded
the document is older than one already accepted on this machine
the document covers no models, or not the model the session runs
The URL must be the https downloads.claude.ai address exactly as given, with no query, fragment, port or credentials. The download is refused in remote, cloud or ssh sessions, with third-party providers such as Bedrock, Vertex or Foundry, and when the allow_model_catalog policy is denied, as it is under HIPAA. To start without the configuration, remove the flag or the environment variable.
Why
This gives Anthropic a way to hand you a signed configuration that changes how Claude Code behaves for a particular model. It does nothing unless you are given a URL. A bad or unsuitable one stops Claude Code from starting.
