No. Most baking powder sold for home baking today in the US is double-acting, but single-acting baking powder also exists and is still used, particularly in commercial baking and in some countries.
Double-acting baking powder contains two types of acid: one that reacts with the baking soda as soon as it gets wet (in the mixing bowl), producing an initial burst of carbon dioxide, and a second, heat-activated acid that reacts once the batter goes into a hot oven, producing a second burst of gas. This two-stage reaction gives bakers more forgiveness — batter can sit for a while before baking without losing all its leavening power, and it produces a more reliable rise. Common double-acting formulas combine sodium bicarbonate with monocalcium phosphate (fast-acting) and sodium aluminum sulfate or sodium acid pyrophosphate (slow, heat-activated).
Single-acting baking powder contains only a fast-reacting acid (often cream of tartar or monocalcium phosphate) combined with baking soda. All the gas is released as soon as the powder becomes wet, so batter must be baked immediately after mixing or it will lose its rising power. Single-acting powders are less common on grocery shelves in North America but are used in some traditional recipes, homemade baking powder mixes, and in certain commercial or artisanal baking contexts where precise timing is controlled.
If a container of baking powder doesn't specify "double-acting" on the label, it's worth checking the ingredient list: the presence of two different acid salts (rather than just one) generally indicates a double-acting formula. When a recipe simply calls for "baking powder" without further specification, it's almost always safe to assume double-acting, since that's the standard product in most supermarkets, but reading the label is the only way to know for certain.