We have data through July from OPEC secondary sources and through June for most other sources. The result looks as above (graph not zero-scaled to better show changes). Iranian production has been falling noticeably for a number of months and is now down by about a sixth of the pre-sanctions level. This ignores the possibility that Iraq is helping Iran to smuggle oil.
So the sanctions are definitely biting - revenue will likely have dropped much more than production (since only a fraction of production is exported and prices paid will have dropped as Iran's few remaining customers use their leverage to extract price concessions). Still, the Iranian response has been to double down on nuclear enrichment. So sanctions are not, thus far, achieving the desired end goal.