Context engineering

As context windows grew and agents got longer-running, the bottleneck stopped being clever instruction phrasing and became information management: what to retrieve, what to summarize, what to keep from earlier turns, what to drop, and what to fetch on demand via tools.

The core insight is that context is a scarce, expensive resource even when the window is large. More context costs more, adds latency, and can actively hurt quality by burying the relevant detail among plausible distractors. Curation beats volume.

In practice it covers retrieval quality and chunking, compaction of long histories, cache-friendly ordering (stable content first, volatile last), context files that give an agent its priors, and tools that let the model pull what it needs instead of being handed everything up front.