Now I'm not sure.
A good hardware current source may run off of 9v but
incrementally it may behave like a 50v source in series with a 10Ω resistor or a 500v source in series with a 100Ω resistor. The second has higher compliance, and, I suppose, may even run off of less than 9v.
Ideally a current source is a voltage source of infinite voltage in series with a resistor of infinitely high resistance such that V/I = 5A (in this case).
One definition of compliance is "the load current's insensitivity to the load." As the load approaches zero impedance, I guess the apparent compliance of a real world current source, even a bad one, approaches infinity.
I could also imagine "negative compliance"; the current actually decreasing with decreasing load impedance, like a power supply with foldback current limiting. With opamps almost anything is possible.