Final answer:
The ad format with the highest reach and lowest CPM among in-stream video formats is typically programmatic video advertising, which automated buying leads to cost efficiency and more strategic ad placements.
Step-by-step explanation:
In the realm of digital advertising, the ad format that delivers the highest reach and has the lowest CPM (cost per thousand impressions) among in-stream video formats is generally recognized to be programmatic video advertising. Programmatic advertising uses algorithms and software to buy and place ads automatically, which can lead to increased efficiency and scale, thus reducing overall costs. Compared to traditional direct buying, programmatic can offer more specific targeting options and real-time bidding, which helps advertisers achieve higher reach at lower costs. Additionally, the use of programmatic enables more strategic ad placements and can optimize campaigns in real-time to ensure the best possible performance