According to an email from Amazon:
"This is a reminder that you will lose access to Alexa Guard in the coming weeks. Starting today, you should not use Alexa Guard to detect smoke alarm, CO alarm, or glass break sound events in your home."
It is replaced by Alexa Emergency Assist which costs $5.99/month. It does have the ability to call emergency services, but it is not 911. Amazon states that emergency calls are answered by Rapid Response Monitoring Services, which I believe is similar to an operator for a monitored home security system like ADT, Brinks, or Vivint.