Should one literally think "I am breathing in long, I am breathing out long." Per the teachings of the Anapanasati Sutta, should one literally think about what they are doing, or focus on the breath itself? 

Meaning, should I think "I am breathing in long," or should I focus on the action of my breath being long?
It is not necessary to think: "I am". The mind should know the action of the breath being long or being short. Also, there is really no need to "focus". When the mind is quiet &amp; silent, the mind will know the breathing. Be as silent, still, upright, awake &amp; alert as possible. 

Note: At the highest level of practise, the Buddha taught to reflect: 


  Monks, whatever form, past, future or present, internal or external, coarse or fine, low or lofty, far or near, all that form must be
  regarded with proper wisdom, according to reality, thus: 'This is not
  mine, this I am not, this is not my self.'
  
  SN 22.59