Anthropic Publishes Claude's System Prompts: What Guides the Chatbot
Anthropic has published detailed release notes for the system prompts behind claude.ai and the Claude mobile apps - the hidden instructions that shape every conversation, from tone to safety behavior.
What happened
Anthropic has published detailed release notes for the system prompts used by claude.ai and the Claude mobile apps - the hidden instructions loaded at the start of every conversation. The documentation covers models from Claude Haiku 3 up to the newest Claude Opus 5 and Claude Fable 5.1.
What is inside the prompt
The system prompt supplies up-to-date context such as the current date and encourages certain behaviors, like always providing code snippets in Markdown. Anthropic says the prompt is updated periodically, that changes apply only to the chat products and not the Claude API, and that newer models ship as fixed snapshots with a single dated entry.
Why it matters
System prompts shape tone, answers and safety behavior, yet users almost never see them. Publishing them gives developers and researchers a reference point for building their own assistants - and shows how quietly a chatbot's behavior can shift between updates.