Sovereign immunity under the Eleventh Amendment reflects the constitutional structure's protection of state dignity and treasury from unconsented federal-court suits by private citizens. The immunity extends beyond suits naming a state directly to suits against state agencies and officials sued in their official capacity for retrospective relief, when a judgment would effectively be paid from the state treasury.

Whether an entity counts as an "arm of the state" for immunity purposes is its own fact-intensive inquiry, weighing state treasury exposure, the entity's degree of autonomy, and how state law characterizes it — a state university or public hospital authority can fall on either side depending on funding and governance structure. Immunity can be lost two ways: the state can waive it, or Congress can validly abrogate it under a constitutional power that permits abrogation, most notably legislation enforcing the Fourteenth Amendment. Local governments — cities, counties, school districts — are generally not treated as arms of the state and do not share this immunity.

A Juricratic simulation treats the arm-of-the-state determination as a threshold dial that can remove an entire branch of relief from the projected trajectory space before the merits are ever reached — useful for showing a user how much of a case's exposure profile depends on an entity classification question that has nothing to do with the underlying facts.

Before filing against a state-affiliated entity in federal court, counsel typically researches whether the entity qualifies as an arm of the state, whether any applicable waiver or abrogation exists, and whether the claim can instead be structured as one for prospective relief against an individual official — a route that can proceed under a separate doctrine even when the state itself is immune.