Every model from every provider at every version I've used has intermingled brilliant perfect instruction-following and weird mistaken divergence.
In this case I can't get 4.5 to follow directions. Neither can anyone else, aparantly. Search for "Sonnet 4.5 follow instructions" and you'll find plenty of examples. The current top 2:
https://www.reddit.com/r/ClaudeCode/comments/1nu1o17/45_47_5...
https://theagentarchitect.substack.com/p/claude-sonnet-4-pro...
Every model from every provider at every version I've used has intermingled brilliant perfect instruction-following and weird mistaken divergence.