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Hello Neil! Thanks for reaching out to us. Right now our API does not have the ability to pull historical data. The post you mentioned that Pro members could access historical data, meaning they can use the Moz Pro tools to view historical data, not necessarily the API. We apologize for the confusion. The good news is that we are hoping to add this functionality to our API in the near future. The ability to pull historical data with the API is absolutely in the works. While we do not have an ETA, you can absolutely expect this soon. Sorry for the confusing verbiage in this post. I will make sure that we adjust this to better reflect our current functionality.