Anthropic reduced Claude Code’s system prompt from 800 tokens to 164 tokens, an approximately 80% decrease, with no performance loss. The announcement was made on July 2, 2026 by engineer Thariq Shihipar at the AI Engineer World’s Fair. This translates to reduced costs and faster response times for every user. This decision reflects a major philosophical shift: recent models like Fable 5 (Mythos-class) perform better with less explicit instruction, as they have internalized enough understanding to handle ambiguity. Shorter system prompts also free up space in the context window, allowing the model to focus more on users’ problems.
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