Chatgpt GPT 5.5 heavy thinking vs Codex GPT 5.5 xhigh

The answer from the support : “xhigh” in Codex refers to the GPT‑5 reasoning.effort setting (more internal reasoning before answering), while “Heavy thinking” in ChatGPT is a UI control that gives the ChatGPT Thinking/Pro model more time to reason; they’re not 1:1 comparable across products, and Codex is also tuned/optimized for agentic coding workflows (edits, diffs, code review) rather than general chat. For strategy/architecture/financial analysis/large document synthesis, ChatGPT “Thinking” (and “Pro” when available) is typically the better fit; use Codex xhigh when the work is primarily code-centric (designing/implementing/reviewing code changes) and you want the agentic coding behaviors.