Chat compaction

Every model can read only so much text at once. When a long chat fills that space, DataMind Oda condenses the older part of the conversation into one summary and continues from it. This page covers when compaction happens on its own, how to run it yourself, and what the summary keeps.

When Oda compacts a chat on its own

Oda watches how full the chat is, and condenses on its own when the conversation crosses the compaction threshold. The context ring in the message box shows the same figure while you work.
By default, the threshold is the lower of 80% of the model's context window and the window minus its reserved output space and a 65,536-token headroom.
The older part of the conversation is replaced by one checkpoint message; the newest messages stay untouched.
A confirmed context overflow also triggers compaction: when a request fails because the context no longer fits, Oda condenses and then retries the request, within its retry budget.
Before it condenses, Oda may first trim oversized tool results out of the request; the trimming runs only once a compaction trigger qualifies. See Tool result pruning and image offload.

Compact a chat on demand

Run /compact in the message box to condense the older part of the conversation yourself, even when the chat has not reached the automatic threshold. It is one of the chat's commands; Chat with Oda lists the others.

Type /compact in the message box and send it on its own. It takes no arguments.
If a turn is still running, or another compaction is active, it does not start and the chat shows Compaction is unavailable because this process has an active compaction, or the agent is not idle. Run it again once the chat is idle.
When it finishes, the chat shows Compacted <n> history items (~<tokens> tokens). The counts are the history items condensed and an estimate of the tokens this freed.

The result is one checkpoint message in place of the older part; the newest messages stay untouched.
Messages you send while it runs wait and start after it finishes; nothing is lost or reordered.
The command itself is not part of what the model reads; it is recorded in the session log.
Only you can run it; it is not something Oda can do with its tools.
If you stop it while it runs, the chat shows Compaction cancelled. Stopping ends your wait, and the cleanup the run needs still finishes.

What the checkpoint keeps

The condensed part becomes one checkpoint message: an automatically generated preamble, then the summary inside a <compacted-summary> frame.
The preamble tells the model the summary is established background: build on it without restating it, and continue without acknowledging it.
The summary follows a fixed outline:
- Primary Request and Intent
- Key Technical Concepts
- Files and Code
- Errors and Fixes
- Pending Jobs
- Current Work
- Next Step
- Critical Context
Compaction works on the conversation's history only: it never shrinks the system prompt, the tool definitions or the start of the session.
The chat keeps its record: every message stays in the conversation, and compaction changes what Oda sends to the model. The marker it leaves, and the summary it opens, are covered in System prompt, context and compaction.

Messages the command can show

When	What appears
There is nothing old enough to condense yet	`No compactable history yet.`
The command is sent with arguments	`Usage: /compact (no arguments)`
A turn or another compaction is still running	`Compaction is unavailable because this process has an active compaction, or the agent is not idle.`
The selected history changed while it ran	`The history selected for compaction changed before it could be replaced. The attempt is recorded in the session log.`
No useful summary could be made	`Compaction could not produce a useful summary. The attempt is recorded in the session log.`
It did not finish cleanly	`Compaction did not finish cleanly; some session history may have changed. Inspect the current session state before retrying.`
It finished, but the chat could not be saved	`Compaction finished, but the session could not be saved.`
It was stopped	`Compaction cancelled.`

Questions, answered

How full does a chat get before Oda compacts it?

Oda condenses on its own when the conversation crosses the compaction threshold: by default, the lower of 80% of the model's context window and the window minus its reserved output space and a 65,536-token headroom. The context ring shows the same figure while you work.

Can I compact a chat before it fills up?

Yes. Send /compact whenever the chat is idle; it condenses the older part of the conversation even before the automatic threshold is reached.

Why is `/compact` unavailable?

A turn is still running, or another compaction is active, so the command did not start. The chat shows Compaction is unavailable because this process has an active compaction, or the agent is not idle. Wait until the chat is idle and run it again.

Is the older part of the chat deleted when it is compacted?

No. The chat keeps its record of every message; compaction changes what Oda sends to the model, replacing the older part with the summary. The marker it leaves in the conversation is covered in System prompt, context and compaction.

What does the summary keep?

The summary follows a fixed outline: Primary Request and Intent, Key Technical Concepts, Files and Code, Errors and Fixes, Pending Jobs, Current Work, Next Step and Critical Context. The work continues from it in place of the older messages.

What happens to a message I send while compaction runs?

It waits. Messages sent during a compaction stay queued and start when it finishes; they are not lost or reordered.

Can I stop a compaction while it runs?

Yes. Stopping it ends your wait and the chat shows Compaction cancelled.; the cleanup the run needs still finishes.

Can I choose which part of the chat gets compacted?

No. The command takes no range or policy arguments: Oda condenses the older part of the conversation and leaves the newest messages as they are. Anything you add after the command is refused with Usage: /compact (no arguments).

Does compaction change the system prompt or the tool list?

No. Compaction works on the conversation's history only; it never shrinks the system prompt, the tool definitions or the start of the session.

Why did `/compact` say it could not produce a useful summary?

Oda could not make a summary smaller than the part it would replace, so it left the chat as it was. The attempt is recorded in the session log, and you can try again when the chat is idle.

What do the warnings about changed history mean?

Two messages mention change. If the chat says the history selected for compaction changed before it could be replaced, the selected part moved on while the run was in progress and nothing was replaced; run the command again if you still want it condensed. If it says the compaction did not finish cleanly, check the chat's current state before retrying. In both cases the attempt is recorded in the session log.