The to: "" broadcast mode for SendMessage in agent teams has been deprecated. The new behavior produces: "broadcast (to: \"\") is no longer supported — send a message per recipient". The team system prompt no longer mentions broadcast capability, directing agents to send individual messages instead.
Evidence
Deprecation message (search for "broadcast (to: \"*\") is no longer supported").
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's release notes agreeFixed subagents resumed via SendMessage not restoring the explicit cwd they were spawned with
