If Opus 4.8 is just slightly better than 4.7 then it maybe ties with GPT 5.4, maybe. And it gets completely outclassed by GPT 5.5 for my workload.

With Anthropic expensive pricing, there's no reason for me to switch from GPT+DeepSeek.

And I bet Mythos is GPT 5.5 tier but too expensive to distribute so they create this security FUD theater.