Weird. New installs usually get some sort on onboarding screen that explains how to activate the new stuff.

The 18.2 Chat GPT stuff can be manually enabled under settings > Apple intelligence > scroll way down > Chat GPT. Once enabled, writing tools and Siri will give you the option to send a query to ChatGPT instead of Apple’s model.

If Siri gets stumped, it will ask if you want to query GPT. Or you can just prompt it to Ask Chat GPT ______.

Writing tools has it buried under “compose” which is at the very bottom of the writing tools sheet.