Prettier historically preserved a newline placed immediately after an opening brace as a signal to keep the object expanded, and there was no way to turn that behavior off. Prettier 3.5 exposed it as the objectWrap option with values "preserve", the existing default, and "collapse".
With "collapse", Prettier ignores the author's line break and fits an object onto one line whenever it is short enough. That produces more consistent output across a codebase and removes the invisible formatting control that surprises people who cannot understand why an object refuses to join up.
The tradeoff is that objects deliberately expanded for readability, such as configuration literals with one key per line, get compacted. Most teams that want consistency also want those to stay expanded, so test the option on real files before adopting it. Changing this setting reformats every affected object, so treat it as a formatting-only commit like any other default change.