GenAI Field Guide

Under the hood (just enough)

Compaction

When the transcript approaches the window, the harness compacts: it summarizes older turns into a few paragraphs, discards the verbose originals (bulky tool outputs first), and continues with the summary as the new head of the conversation.

≈1 min
40 turns Messages · Replies · Bulky tool outputs Summary: turns1–30 A few paragraphs Last 10 turns Recent detail stays Details can disappear A precise number becomes a general note
A specific number from eighty turns ago may survive only as "we discussed unit strength figures."

What this means for you

Consequence What you do
Detail is lost, silently. If something must survive, write it to a file or a project. The transcript is not durable.
Compaction is a design choice of the harness, not a property of the model. Every product does it with different, unpublished rules. Teach yourself the mechanism, not the thresholds. Assume it can happen at any time in a long session.
Tool outputs (logs, search results, file contents) are the first thing summarized or dropped. "It worked last time" can turn into "it forgot the error" after compaction.