I guess yes, that's a harness difference, and you can also configure CC as a harness to behave very differently, but still with same harness and guidance, "to me" there's still a difference in terms of Opus 4.6 and e.g. GPT 5.4 or which GPT model do you use? I've been using Claude Code, Codex and OpenCode as harnesses presently, but for serious long running implementation I feel like I can only really rely on CC + Opus 4.6.