Alternatives to Claude

Tools that do the most similar job to Claude, closest first.

• Claude Opus 5.5 — Anthropic's first model in their new Claude 5.5 family
• ECC — The agent harness performance optimization system. Skills, instincts, memory, security, and research-first…
• system_prompts_leaks — Documented system prompts from Anthropic - Claude Fable 5.1, Opus 5.5, Claude Design, Claude Code. OpenAI -…

Opening Liz…