Anthropic Reduces Claude Code System Prompts by 80%, New Model Maintains Coding Performance Without Strict Rules

Anthropic engineers disclosed that the team reduced approximately 80% of the system prompts for Claude Code for the latest Claude model, and coding evaluations showed no performance degradation. Early versions contained numerous strict rules in the prompts (such as prohibiting multi-line comments, etc.) due to insufficient model capabilities, but after the new model acquired autonomous decision-making capabilities, these rules instead triggered instruction conflicts and divergent thinking. The new strategy shifted to describing goals (such as "write code that matches the surrounding code") and distributed instructions across tool descriptions and on-demand enabled skill modules. The team explicitly views prompt bloat as technical debt, believing that as model capabilities improve, instructions should be simplified rather than stacked.