Compaction Forgets What You Knew

Wed, 14 Oct 2026 10:00:00 -0400

The moment I dread in a long agent session is the one where the context meter runs out, auto-compaction kicks in, and the agent comes back from its little nap sounding exactly as confident as before while knowing noticeably less. It still remembers the task. What it’s lost is the reason we ruled out the obvious fix two hours ago, so it goes and tries the obvious fix again.

I’d assumed this was a me problem, probably caused by letting sessions run too long, until I read Stencil’s write-up on Snapcompact.¹ Most of the post is about their answer to it: rendering the context as images and feeding the model pictures of its own transcript, which I’ll come back to. The part that stuck with me is a short section near the top called “The Case Against Compaction”, where Can Bölük says that in every harness they’ve used, compaction “cripples” the model “to the point where you would have been better off with a completely new session.”

Context-Engineering on Thoughts and code

Compaction Forgets What You Knew