[DOCS] `ultrathink` now enabled by default (not in CHANGELOG)

Documentation Type

Missing documentation (feature not documented)

Documentation Location

https://github.com/anthropics/claude-code/blob/main/CHANGELOG.md (as of v2.1.7)

Section/Topic

ultrathink default behavior in CHANGELOG.md

Current Documentation

_No response_

What's Wrong or Missing?

I recently saw on @bcherny's X account that ultrathink has become the default.

Thinking is on by default everywhere, ULTRATHINK doesn’t really do anything anymore

https://x.com/bcherny/status/2007892431031988385

However, this change does not appear to be mentioned in CHANGELOG.md. If that is the case, this is a user-visible change, so it would be valuable to document it in CHANGELOG.md.

Suggested Improvement

It would be helpful if text like the following, which has been shared on X, were included in the appropriate release section of CHANGELOG.md.

Thinking is on by default everywhere, ULTRATHINK doesn’t really do anything anymore

Impact

Low - Minor confusion or inconvenience

Additional Context

_No response_