Claude's web interface (claude.ai) and mobile apps use a system prompt to provide up-to-date information, such as the current date, at the start of every conversation. The prompt also encourages certain behaviors, including always providing code snippets in Markdown. These system prompt updates are periodically revised to improve responses but do not apply to the Claude API.

The documentation lists dated entries for each model generation. Where a model has multiple entries, updates between versions are bolded. Starting with the Claude 4.6 generation, each model ID represents a single fixed snapshot, so those models have only one entry.

Recent versions include Claude Opus 5 (July 24, 2026), Claude Fable 5 (June 9, 2026), and Claude Opus 4.8 (May 28, 2026). Earlier generations such as Claude Sonnet 4, Claude Opus 4, and Claude 3.5 series show multiple dated updates throughout 2024 and 2025.

This version history reflects ongoing refinements to the default instructions that shape Claude's behavior in consumer-facing products, separate from the API which operates without these automatic system prompt injections.