{"version":"2.1.86","anchor":"file-read-caching-unchanged-since-last-read","canonical_anchor":"file-read-caching-unchanged-since-last-read","heading":"File Read Caching (\"Unchanged since last read\")","tier":null,"area":null,"scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.86\/e\/file-read-caching-unchanged-since-last-read","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.86","markdown":"### File Read Caching (\"Unchanged since last read\")\n\n**What**\n\nWhen the Read tool is used on a file that hasn't changed since a previous read in the same conversation, Claude now returns a short notice instead of re-reading the entire file, saving context window space.\n\n**Details**\n\n- Displays \"Unchanged since last read\" in the tool output\n- The full message tells Claude to refer to the earlier Read tool result instead of re-reading\n- Controlled by the `tengu_compact_line_prefix_killswitch` feature flag (enabled when killswitch is off)\n- Helps conserve context window tokens in long conversations with repeated file reads\n\n**Evidence**\n\nRead caching message (search for `\"File unchanged since last read\"`) \u2014 `kf1()` at line ~163425"}