The EHT is an evolving network of telescopes. Observations in April 2017 were carried out with eight observatories in six geographical locations around the globe. For the observing campaign in 2018, one new telescope was added to the array, totalling nine observatories at seven sites.
No observations with the EHT array were performed in 2019 and 2020. We plan to add additional observatories to the array for future observational campaigns -- two more are expected to join the array for observations in 2021, totalling eleven observatories at nine different locations around the globe. You can find a virtual tour of all EHT observatories here.