{"version":"2.1.120","anchor":"lean-prompt-mode-condensed-tool-descriptions","canonical_anchor":"lean-prompt-mode-condensed-tool-descriptions","heading":"Lean Prompt Mode (Condensed Tool Descriptions)","tier":null,"area":null,"scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.120\/e\/lean-prompt-mode-condensed-tool-descriptions","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.120","markdown":"### Lean Prompt Mode (Condensed Tool Descriptions)\n\n**What**\n\nA new prompt optimization mode that significantly reduces system prompt token usage by sending shorter, denser tool descriptions to capable models.\n\n**Usage**\n\n`CLAUDE_CODE_LEAN_PROMPT=1 claude # force enable via env var` **Details** - When active, tool descriptions for Grep, Glob, WebFetch, Write, Edit, WebSearch, TodoWrite, Bash, and the Task\/Explore agent are replaced with much shorter versions - Example: the Grep tool description goes from a multi-paragraph usage guide to a compact 4-line summary - The Explore agent description is refined to emphasize it is a \"read-only search agent\" not suitable for code review or cross-file analysis - Activated by the `CLAUDE_CODE_LEAN_PROMPT` environment variable, or gradually rolled out via the `tengu_vellum_lantern` feature flag - Currently limited to Opus 4.6+ and Opus 4.7 models **Evidence** Lean prompt gate function checks `CLAUDE_CODE_LEAN_PROMPT` and `tengu_vellum_lantern` \u2014 search for `\"CLAUDE_CODE_LEAN_PROMPT\"`\n\n- Flag `tengu_vellum_lantern`: Off in both readings (read for one account on one subscription tier against v2.1.120; this account: off, anonymous baseline: off, compiled default: no gate table built for this version) These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release."}