Templates - old and new in same configuration.yaml?

I know we have changed from old style to new style templates. I know they have different options. What I can’t actually figure out is whether you can have both in the same configuration.yaml. I have some old style

sensor:
  - platform: template etc

and I want to add a new style

template: 
  sensor: etc

Can they co-exist? Or do I have to convert all my old style to new style before I can start with the new?

Yes, I think you can. When I migrate my legacy template one by one to the new modern template, both sensors from different headers shows up fine.

Thanks, that’s not the problem with my new template then.

Try adding a dash-

template:
  - sensor:
      - name: "Average temperature"
        unit_of_measurement: "°C"
        state: >
      - name: "Average temperature"
        unit_of_measurement: "°C"
        state: >

  - binary_sensor:
      - name: "Has Unavailable States"
        state:
      - name: "Has Unavailable States"
        state:

  - trigger:
      - platform: time_pattern
        # This will update every night
        hours: 0
        minutes: 0
    sensor:
      # Keep track how many days have past since a date
      - name: Not smoking
        state: '{{ ( ( as_timestamp(now()) - as_timestamp(strptime("06.07.2018", "%d.%m.%Y")) ) / 86400 ) | round }}'
        unit_of_measurement: "Days"

  - trigger:
      - platform: time_pattern
        # This will update every night
        hours: 0
        minutes: 0
    sensor:
      # Keep track how many days have past since a date
      - name: Not smoking
        state: '{{ ( ( as_timestamp(now()) - as_timestamp(strptime("06.07.2018", "%d.%m.%Y")) ) / 86400 ) | round }}'
        unit_of_measurement: "Days"

I had eventually figured it out, and in fact I had too many dashes (which I had not got right in my above example either.) Thanks for your help.