Context and compression

Every reply your agent writes is produced from a bundle of text assembled fresh for that turn. The brief is one part of that bundle. Knowing what the other parts are explains most of the behaviour people find surprising, including why a long brief is expensive and a long conversation is not.

What the agent reads on a turn

Four layers are assembled, in this order, plus anything retrieved for the question being asked.

Layer	What it is	Changes
1. System	Your published brief, plus the model and channel	Only when you publish
2. Long memory	What is known about this customer across conversations	Slowly
3. Session summary	A condensed account of earlier in this same conversation	As the chat goes on
4. Short memory	The most recent turns, verbatim	Every turn

Layers 2 to 4 are managed for you and vary per conversation. Layer 1 is your brief: identical on every turn, and the only one you author.

On top of those, two more things arrive when they are relevant:

• Retrieved knowledge. Passages pulled from your knowledge base and from any files the customer shared into this conversation, merged by relevance and de-duplicated.
• Tools. Descriptions of what the agent is allowed to call.

Layers 2 and 3 exist so a long conversation does not become an expensive one. Rather than resending an hour of chat, the platform keeps a summary of the older part and only the recent turns in full. Roughly the last twenty messages carry verbatim; anything purged for data protection is excluded and never rebuilt.

The one layer you author is the one that never varies

This is the thing worth internalising.

Layers 2, 3 and 4 change per customer and per conversation, and the platform manages their size for you. Layer 1 is the brief, it is identical on every turn, and it is entirely yours.

So the brief is a fixed cost paid on every reply, to every customer, for as long as the agent runs. A hundred wasted words in a Context prompt is not a hundred wasted words. It is a hundred words times every conversation you will ever have.

That is the whole argument for keeping the brief terse, and it is why the editor puts a number on it.

Reading the numbers

The Prompts editor shows the running cost in the composed panel.

Reading	Means
Context cost	What every turn will carry once you publish
Currently live	What the agent is paying right now
After you publish	What it will pay if you publish the working copy

The number quoted is the compacted size, not the raw size, because compacting is what publish actually writes. Quoting the raw figure would have you budgeting against a bill the agent never receives.

If the two figures differ, you have unpublished changes.

Two ways to make it smaller, and they are not the same

People treat these as one feature. They are opposites, and the difference is about who is allowed to change your words.

Compact: automatic, lossless, always on

Whitespace only. Extra blank lines and stray indentation are trimmed when you publish. Nothing is reworded, nothing is dropped, and no model is involved.

You do not turn this on. It already happened. When the editor says spacing is already trimmed, or that a prompt is as short as it safely gets, that is compacting telling you there is no free space left.

Shorten with AI: manual, lossy, proposal only

This is the lever that can actually shrink prose, and it is deliberately awkward to use, because a reworded rule is a changed rule.

The rules it operates under are worth stating plainly:

• It never writes. You get a proposal and a diff. Accepting is a separate, explicit action, and accepting is a normal edit, so it creates a version.
• It never runs on publish, and it never runs during a customer conversation. Nothing is being quietly rewritten behind you.
• Rules are excluded. A Rule prompt gets whitespace tidying only, never rewording. This is the single most dangerous place for a model to be helpful, so it is not allowed to be.

The dropped-invariant check

When a shortened version comes back, it is scanned against the original for things that must not vanish: numbers, prices, URLs, and code blocks. Anything present before and missing after is flagged for you.

This check is deterministic, needs no model, and exists because of one specific failure: a price silently disappearing from a paragraph that otherwise reads fine. A human skimming a diff will catch a changed sentence and miss a missing number every time.

Flags do not block you. They tell you where to look before you accept.

A practical order of operations

When the brief is too big, work in this order. It goes cheapest and safest first.

1. Disable prompts you are not sure about. Free, reversible, and it answers the real question, which is whether a prompt is earning its tokens.
2. Move facts to knowledge. A fact in knowledge is retrieved only when relevant. The same fact in a Context prompt is paid for on every turn, including all the turns where nobody asked.
3. Cut samples to the ones that teach. Three well-chosen examples beat twelve near-duplicates, and near-duplicates are the most common form of brief bloat.
4. Then shorten with AI, and read the diff.

Most briefs that feel too big have a Context prompt doing the job of a knowledge base. Step 2 usually finds it.

When answers get cut off mid-sentence

Worth knowing because it looks like a context problem and is not.

If replies stop partway through a sentence, the output limit is too low rather than the context being too big. An unset maximum is not an unlimited one; leaving it unset means inheriting a default that is smaller than most people expect. See Providers and models.