Long Claude Code sessions get compacted, and Claude often seems dumber afterwards. Fast-Jev Compaction is an open-source plugin that makes room without rewriting a word of your conversation. Here is what it keeps, what it drops, who decides, and how to install it.
Fast-Jev Compaction on GitHub: https://github.com/tamaratran/fast-jev-compaction
What goes wrong with /compact
When a Claude Code session fills its context window, /compact (or auto-compaction) asks Claude to rewrite the conversation so far into a shorter summary, and the summary replaces the chat. A summary is lossy: the exact file path, the exact error message, the rule you set at the start ("never edit src/generated") can disappear, and Claude carries on without them. That's the "it got dumb after compacting" feeling.
Fast-Jev Compaction is an open-source Claude Code plugin (MIT) that replaces that summary. It never rewrites anything. It makes room by deleting old tool calls and tool results that are no longer needed, and hands Claude back the original messages.
What it keeps and what it drops
| Part of the session | What happens |
|---|---|
| Your messages | Kept word for word, in order |
| Claude's replies | Kept word for word, in order |
| The first message and the newest few | Pinned: never touched |
| An old tool call still worth knowing about | Kept, its output cut to the first few hundred characters plus a note |
| An old tool call and output nobody needs | Removed together (for example a file Claude read long ago) |
Tool output is usually most of a long session: every file Claude opened, every test run, every search. That's what gets cleared, and Claude can always re-run a tool if it needs the result again.
The second AI that decides
Before anything is deleted, a second model called Jev (from TypeSafe AI) reads the whole conversation and answers two questions about every old tool call:
- Keep the call? Does it still matter that this was done, with these inputs?
- Keep the result word for word? Is its output still needed, and would re-running the tool not do?
It's like someone asking "are you still eating this?" before they throw out the leftovers. If Jev fails, or it can't free enough space (common in short sessions), the plugin falls back to Claude Code's normal summary, so compaction still works.
Free, for your email
Get the full setup steps + the copy-paste setup prompt
The rest of this guide (2 more sections) opens right here. The setup prompt, one paste into Claude that sets it all up, comes by email only. Use your real address.
Unlocks: Set it up · Good to know
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