The deal is an indicator that advertisers are really starting to take Twitter seriously as a big media vendor. It is reminiscent of a previous deal Twitter struck last April with Publicis, another ad agency group. That one was worth $200 million.
Similar bulk media buying deals have been done with Instagram ($100 million), YouTube ("tens of millions") and Facebook ($500 million).
Whether it will move the stock or not is a separate question. Investors have been focused on Twitter's slow user growth. They appear to be unmoved by its robust revenue growth.
This new deal strengthens the argument that Twitter's business model is actually different than that of Facebook or Google - Twitter may not be the mass medium for ordinary people that those other companies provide. Rather, it may be valuable as a specialist medium for people who need a lot of current news.
Disclosure: The author owns Twitter stock.