Unclear Which version any given account receives when the environment variable is not set is decided by the server.
When a conversation gets too long, Claude Code compacts it: it writes a summary of what happened so far and continues from that summary. Until now one fixed set of instructions produced every summary. Claude Code now picks between four versions of those instructions:
control, the default, which is used when nothing else is chosenleanshortcapped
The three versions other than control use different instructions and ask for the summary on its own, without the separate written analysis step that comes before it. The lean version also points to the saved transcript (the file where the full conversation is stored), but only when that file exists.
You can choose the version yourself with the CLAUDE_CODE_CURRIED_TRINKET environment variable (a setting you put in your shell before starting Claude Code). If it is not set, a remote setting decides, and the built-in fallback is control. The version used is recorded with each compaction.
This is a test of different ways to write compaction summaries. Because the summary is what Claude works from after compaction, how Claude picks up a long task afterwards may differ depending on which version was used.
Which version any given account receives when the environment variable is not set is decided by the server.