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Resuming a session without losing everything
Opening a fresh session attached to the same project and asking it to resume the context costs less and moves faster than extending a session that has already grown heavy.
A session that grows longer day after day ends up reloading everything it contains with every new message: the longer it runs, the heavier each reply weighs on the quota and the longer it takes to arrive. The answer is not to close it without keeping anything, it is to open a new one inside the same project and explicitly ask it to pick up the thread.
Why extending weighs more than resuming
Every message added to a session stacks on top of all the previous ones, reopening an old session reloads the whole thing before it even deals with the new request. A session opened on Monday and extended every day until Friday carries, by Friday, five days of conversation to reread before the slightest reply. This volume being reread grows a little more with every message, whereas a fresh session starts light. This logic extends the reflex of several short sessions grouped inside a project rather than a single marathon session extended day after day.
What a project keeps for you
Closing a session does not make what matters disappear, provided it is attached to a project. The files and the permanent instruction attached to the project that holds the context stay in place and are reread by any new session opened inside it, without needing to be pasted back in. What does not follow automatically is the fine detail of the ongoing conversation, the precise exchange from the day before on a particular point, it is that detail you must explicitly ask it to resume.
The formula fits in one sentence, written as the first message of a new session:
Avant de commencer, résume ce que nous avons déjà établi dans ce projet sur ce sujet.Claude then rereads the files and the instruction attached to the project, and hands back a starting point rather than a blank page. What it does not do is reopen the previous conversations: whatever is written nowhere in the project will not come back, unless you hand it back yourself.
When to close, when to carry on
A session that has just begun, on a subject closed within the hour, does not need this treatment. The signal that should trigger opening a fresh session is a felt slowness or a reply that starts mixing several subjects handled on previous days, that is the moment to close it and start again, inside the same project, with a request to resume.
Resuming context rather than extending
A person works in a Cowork session attached to a project for four consecutive days, with several subjects handled each day. On the fifth day, she closes that session and opens a new one, attached to the same project, writing as the first message a request to summarise what has already been established on the day's subject. The new session mentions the files attached to the project and a point discussed on the third day.
Write in one sentence what this situation establishes, and in one sentence what it does not establish.
What this establishes: This result establishes that the new session, attached to the same project, has access to the files and to the instruction attached to it.
What this does not establish: It does not establish that the new session holds the detail of the exchanges from the previous days: whatever was not written into the project does not come back on its own.
The three most common miscalibrations
- Too broad This result shows that the new session has the entirety of the exchanges from the previous four days, in full detail.
- Too narrow This result shows nothing more than the fact that a file has a name recognisable by Claude.
- Beside the point It establishes that the point from the third day mattered more, for this subject, than those of the other three days.
- A session extended day after day reloads, and therefore repays, all of its content with every new message, which weighs down every following reply.
- The files and the permanent instruction attached to a project remain available to any new session opened inside it, without being pasted back in by hand.
- The precise detail of an exchange from the day before does not automatically follow a new session, it must be explicitly requested in the first message.
- A reply that slows down or mixes several old subjects is the signal to close the current session and open a fresh one inside the same project.
As the first message of a new session attached to the project, ask Claude to summarise what has already been established on the subject, then compare that summary to what you already knew: whatever is missing is what the project did not carry.
Every datable claim in this lesson links here to the public text behind it. A source that does not open proves nothing.
- Anthropic, organising your tasks with projects in Claude Cowork consultée le 2026-09-02