I am an American citizen but have never lived in the US. Do I need to fill a W8-BEN or a W-9?
Yes, you do.  You also need to file a tax return every year, and if you have more than $50k of total savings you need to declare this every year.
Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
I am an American citizen but have never lived in the US. Do I need to fill a W8-BEN or a W-9?

### Response:
Yes, you do.  You also need to file a tax return every year, and if you have more than $50k of total savings you need to declare this every year.