A major characteristics of a firm operating at a long-run equilibrium position is that

In the long-run equilibrium position for a firm, **all costs are variable**. This is because the long-run is a period sufficiently long for firms to adjust all factors of production. They can expand or reduce their capacity, acquire new technology, or even enter and exit industries depending on market conditions.

Unlike in the short-run where some factors (like buildings and machinery) are **fixed** because they cannot be changed immediately, in the long-run, firms have the flexibility to alter all their inputs. This means that firms can choose the optimal scale of operation where the average cost of production is minimized, leading to a position where profits are maximized if the market structure allows.

So, in summary: In the long-run, a firm operates where **all costs are variable**, allowing complete adjustment to maximize efficiency and competitive position in the market.