If the issue comments are to be believed it could be related to the codex system...

geophph 38 days ago | parent | context | favorite | on: GPT-5.5 Codex reasoning-token clustering may be le...

If the issue comments are to be believed it could be related to the codex system prompt itself so likely just the harness. I agree the wording is weird but they appear to be referencing GPT 5.5 in Codex because yeah there isn’t a GPT5.5 Codex model.