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anchor

Sessions and context

Sessions

Section titled “Sessions”

Every session is saved as you go, in ~/.anchor/sessions/, as a JSONL file readable only by you.

Terminal window
anchor --resume            # the latest session in this directory
anchor --resume 20260928   # a session by id, or a unique prefix of one

Resuming re-shows the last three turns so you can see where you left off. Sessions from -p and --json runs can be resumed too, interactively or with another -p:

Terminal window
anchor -p "find the bug in the parser"
anchor --resume -p "now write a test for it"

/sessions lists the ten most recent sessions for the current directory, with their first message.

Context

Section titled “Context”

A model can only see so much at once. anchor keeps the conversation under the model’s context window automatically. You can check how full it is with /context:

› /context
~84,120 of 200,000 tokens (42%), 57 messages
Session so far, including sub-agents: in 612,004 · out 18,331 · cached 540,212

The numbers come from the provider’s own usage reports. When a provider doesn’t report usage, anchor estimates, and says so.

What happens as it fills

Section titled “What happens as it fills”

When the context reaches 80% of the window, anchor works through these steps, stopping as soon as there’s room:

  1. Summarize older turns. The model writes a summary of the earlier conversation, which replaces those turns. Recent whole turns are kept word for word, up to 20% of the window, and the current turn always is. A summary that isn’t smaller than what it replaces is rejected.
  2. Trim old tool content. Large old tool results become a short placeholder with a 300-character preview and a note to re-run the tool with a narrower range. Large old tool arguments, like the content of a file write, become a character count, since the file on disk already has them.
  3. Drop the oldest steps of the current turn. For one very long turn, anchor removes its oldest steps and puts a note after your request listing what they did. A tool call is never separated from its result.

The latest step is never trimmed or dropped, because the model hasn’t seen its results yet.

If the provider still reports the request is too long, anchor reduces the context once more and retries.

By hand

Section titled “By hand”
  • /compact summarizes older turns now.
  • /clear forgets the conversation entirely.

The context window size comes from the model family, or provider.contextWindow in the config.