Anthropic secretly works on new models named Claude Sonnet 4 & Opus 4, which is believed to be one of the most advanced AI models from the company.
According to Anthropic’s web configuration files, recently updated Updated to include references to Opus 4 and Claude Sonnet 4.
Anthropic has made sure to customize the internal configuration file as you can see above. Listed “Claude 4,” “Claude Sonnet 4,” & “Claude Opus 4.”
These models appear to be from the Claude 4 Series, which we believe could be Anthropics smartest models ever.
The references indicate that Claude Sonnet 4 or Opus 4 is being tested or promoted within the company, with warnings such as “Not intended for use in production” and “strict rates limits”meaning they are still under development or early acces.
There are also references to features such as “show_raw_thinking,” that point to reasoning abilities.
Anthropic will host a Claude Code event on May 22. We don’t know if this event is connected to the new models.
