Effective Context Engineering for AI Agents

Anthropic's reframing of prompt engineering as the strict subset of a larger discipline: managing the entire token budget across system prompts, tools, examples, message history, and retrieved data. Argues the central question has shifted from 'what words do I send?' to 'what configuration of context is most likely to generate the desired behavior?' Diagnoses the most common failure mode — bloated tool sets with ambiguous decision points — and gives concrete techniques for compaction, summarization, and tool curation. The companion piece to Building Effective Agents.