Its high, but it’s really not that excessive over the course of a day: https://cspinet.org/eating-healthy/ingredients-of-concern/ca...
So yeah, two freaking massive 20oz pours of highly caffeinated coffee will get you to around 1 gram.
But FWIW the daily recommended dose is 400mg. 1g is a ton of caffeine and way beyond what you would get to by sipping on coffee throughout the day (it's 10+ cups of drip).
I cannot find where the number originates, but there is at least one study @ https://www.sciencedirect.com/science/article/pii/S027869151... which explicitly claims "vidence supported consumption of ≤400 mg/day in adults is not associated with overt, adverse effects."