GPT 5.5 does not have the same capabilities as Mythos. There is a separate 5.5-Cyber model which is the Mythos “equivalent”, but it is similarly restricted access like Mythos. Per OpenAI, the major difference is the built-in safeguards that 5.5 (and other models have), where 5.5-Cyber does not have these safeguards and is more “permissive” for security work.
See https://openai.com/index/gpt-5-5-with-trusted-access-for-cyb...