Total speculation: As the software world shakes out the many hidden vulns in their software, big AI will try to limit the access while it gets ironed out. Once the big projects/systems are reasonably patched after being vetted by SOTA models, the models will be released to the public. I don't think there's a scenario where Mythos-level or better models stay closed permanently.
The problem for Anthropic, is that ChatGPT-5.5 is noticeably better than Opus 4.7. The longer they hold back Mythos, the more people will drop their Claude subscription (I have) in favor of an OpenAI subscription.