Unclear It is not clear whether this check is the one that decides fork mode, so whether CLAUDE_CODE_FORK_SUBAGENT=0 still turns forking off everywhere is unsettled.
The attribution block is a short block at the start of the system prompt (the standing instructions sent to the model) that carries details such as the client version. When a project is supplied, it can now also carry two project fields, cc_project and cc_project_src. Setting CLAUDE_CODE_ATTRIBUTION_HEADER to 0 still leaves the whole block out.
A separate check tied to forked subagents has also changed. Forked subagents are helper agents that Claude starts as copies of the current conversation. The check used to pass unless CLAUDE_CODE_FORK_SUBAGENT was set to turn it off. It no longer reads that variable. It now fails whenever CLAUDE_CODE_REMOTE is set, and otherwise depends on two other internal conditions.
The second change can affect when forked subagents are available. If you rely on CLAUDE_CODE_FORK_SUBAGENT to turn fork mode off, note that this one check no longer looks at it.
It is not clear whether this check is the one that decides fork mode, so whether `CLAUDE_CODE_FORK_SUBAGENT=0` still turns forking off…
Changed fork subagents (subagent_type: "fork") to be on by default in claude -p, the Agent SDK, the desktop app and VS Code, as they already…