How much Magento context can I cram into one prompt before it falls over?

Claude Opus / Sonnet 4.x has a 200K token context (and a 1M variant). Practical limit for Magento work is closer to 40–60K tokens of relevant code — anything more and the model starts to confuse module boundaries. Strategy: don't paste the whole module; paste the interfaces + di.xml + schema.graphqls + the one file you want changed. Use @-references in Claude Code to lazy-load supporting files only when needed. Token-count cheat: 1 line of PHP ≈ 8 tokens, 1 line of XML ≈ 12, 1 line of GraphQL ≈ 6.