Adaptive System Prompt Identity

What: Claude Code now uses different identity strings based on operational context (interactive CLI vs non-interactive SDK usage).

Details:

• Interactive CLI mode: "You are Claude Code, Anthropic's official CLI for Claude."
• SDK with custom system prompt: "You are Claude Code, Anthropic's official CLI for Claude, running within the Claude Agent SDK."
• SDK without custom prompt: "You are a Claude agent, built on Anthropic's Claude Agent SDK."
• Vertex AI provider always uses the standard CLI identity
• Enables context-aware behavior based on how Claude Code is being used
• Evidence: Identity selection function A$1() at line 366028, identity strings at lines 366024-366027