FrontierAugust 9, 2026via Simon Willison
Quoting Claude Opus 5 system prompt
Why it matters
Transparency into frontier-model design: the system prompt reveal provides practitioners and researchers direct insight into how Anthropic instructs its most capable model — rare candor on steering, values, and capability constraints from a top lab.
Key signals
- Claude Opus 5 system prompt publicly available via Simon Willison
- Direct window into Anthropic's model steering and instruction design
- Flagship model architecture and values constraints documented
- Published August 9, 2026 — recent disclosure
The hook
Claude Opus 5's actual system prompt is public. Here's what Anthropic actually tells its flagship model to do.