It's hard to say how unreasonable it is without knowing what the API you're supposed to implement looks like. Regardless of how objectively unreasonable it is,

It's hard to say how unreasonable it is without knowing what the API you're supposed to implement looks like. Regardless of how objectively unreasonable it is, there is also the issue of how much you want the job, and if that is outweighed by the unreasonableness of the request. Perhaps you should also consider this an early red flag that XCorp might not be so great. I would look at it this way: if you want the job and can spare the time, give the assignment your best shot; otherwise if you could spend 4 hours looking for other jobs to apply to that have more reasonable application procedures, do that instead. However, whether you decide to do the assignment or not, you should tell the company that you consider the assignment unreasonable and why. Our sector is filled with shitty/unreasonable hiring practices, and I think as candidates we have a responsibility to provide feedback about those practices to provide pressure on the industry to change them. If XCorp starts hearing from a lot of their candidates "Sorry, that's unreasonable, I'm not proceeding", then they will need to revise their hiring process if they want to keep their potential talent pool open. If you decide to continue with the process and do the assignment, then the feedback also works to your benefit by signalling that you are an independent thinker who is willing to give constructive feedback on internal processes: if the company doesn't like that then, well I really wouldn't want to work there anyway.