New York Times:

For the past year, the two companies have been coordinating behind the scenes to make Alexa and Cortana communicate with each other. The partnership, which the companies plan to announce early Wednesday, will allow people to summon Cortana using Alexa, and vice versa, by the end of the year.

Important to note that both companies have tried to take on Apple, Google, Samsung, et al, in the smart phone marketplace. And both companies have failed to make a dent. Without a major smartphone partner, not sure this partnership will have much of an impact.