Simon Willison’s Weblog

Our evaluation of OpenAI’s GPT-5.5 cyber capabilities. The UK's AI Security Institute previously evaluated Claude Mythos: now they've evaluated GPT-5.5 for finding security vulnerability and found it to be comparable to Mythos, but unlike Mythos it's generally available right now.

# 11:03 pm / ai, openai, generative-ai, llms, anthropic, claude, ai-security-research, gpt

Codex CLI 0.128.0 adds /goal (via) The latest version of OpenAI's Codex CLI coding agent adds their own version of the Ralph loop: you can now set a /goal and Codex will keep on looping until it evaluates that the goal has been completed... or the configured token budget has been exhausted.

It looks like the feature is mainly implemented though the goals/continuation.md and goals/budget_limit.md prompts, which are automatically injected at the end of a turn.

# 11:23 pm / ai, openai, prompt-engineering, generative-ai, llms, coding-agents, system-prompts, codex, agentic-engineering