Over 80% of Claude Code's system prompt cut for Opus 5 and Fable 5
anthropic claude
| Source: HN | Original article
Claude Code's system prompt has been significantly reduced for Opus 5 and Fable 5. Over 80% of the prompt was removed.
Developers of Claude Code have significantly reduced the system prompt for the latest models, Opus 5 and Fable 5, by over 80%. This change was made without noticing any measurable loss in coding evaluations, indicating a more efficient use of the system prompt. As we reported on July 25, Claude Opus 5 has been making waves with its near Fable performance at half the price, and this update further refines its capabilities.
The reduction in system prompt is significant because it streamlines the interaction between developers and the model. Previously, explicit verification instructions were necessary, but with Opus 5 and Fable 5, such instructions can actually cause over-verification. By removing these redundant steps, developers can work more efficiently with the models. This change reflects the evolving understanding of how to effectively interact with advanced AI models like Claude Code.
As developers begin to work with the updated Opus 5 and Fable 5 models, it will be important to watch how these changes impact the overall performance and usability of the models. The documentation for Claude Code has already been updated to reflect the new best practices for prompting Opus 5, and developers are advised to remove explicit verification instructions from their prompts to avoid over-verification.
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