It depends on where you're subscribing. Please see below.
Subscribing Directly with AMC
When you subscribe at www.amcplus.com and complete your sign-up there, a 7-day trial is available.
Subscribing Through Apple, Amazon Prime or Roku
Currently each of these providers is offering a 7-day trial, but make sure to check during your sign-up process or contact their support team if you have further questions.
Subscribing Through a TV provider
Visit your preferred provider's website for free trial info.