Anthropic cuts Claude Code’s system prompt by 80% for Opus 5 and Fable 5
0x7Lee · reddit · 2026-07-25
Anthropic says it cut Claude Code’s system prompt by more than 80% for Opus 5 and Fable 5, shrinking it from roughly 800 tokens to 164.
The engineer’s explanation is that newer models no longer need as much explicit hand-holding. Anthropic says the examples used in the old prompt had started to constrain the model rather than help it, and the company saw no measurable drop on coding evals after the cut.
The post argues this marks a shift in prompt engineering: for stronger models, the system prompt may move from controlling behavior to simply framing the task.
Related event: Anthropic Slashes Claude Code System Prompts by Over 80%(11 posts)→
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