Currently the International Space Station and the Chinese Tiangong space station have about 1350 m³ of pressurised volume with breathable air. Moon bases, Mars bases and other space habitats could increase this in future. A cubic kilometre would be one billion cubic metres of artificial atmosphere. Will this happen by 2050?
For avoidance of doubt, this refers only to artificial human-created volumes in our solar system. If we happen to discover a breathable atmosphere on an exoplanet, that would not count.
Update 2025-02-17 (PST) (AI summary of creator comment): Important Update:
Volume qualifies only if it is filled with breathable atmosphere.
For example, a natural cave (e.g., on an asteroid, moon, or planet) will count only if its interior is converted to a pressurised, breathable environment.
1,000