This joint effort announced today by the ESA.
FIFA 19 Ultimate Team

The Entertainment Software Association (ESA), yes that one, announced today that Microsoft, Sony, and Nintendo will now have required policies that ensure the odds of loot boxes are known on their platforms. These odds will be shown on any and all paid loot boxes in games that are developed for their platform.

This comes straight from the ESA's chief counsel for tech policy during a workshop on loot boxes held by the Federal Trade Commission.

"Specifically, this would apply to new games and game updates that add loot box features, and it would require the disclosure of the relative rarity or probabilities of obtaining randomized virtual items in games that are available on their platforms."
Additional information on this new initiative went up today in a blog post on the ESA's website. These new policies will begin to be enacted beginning some time in 2020. In addition, a number of publishers throughout the industry have also agreed to implement a similar disclosure policy by the end of 2020.

Some of the publishers that have agreed to this include Activision Blizzard, Bandai Namco, Bethesda, Bungie, Electronic Arts, Take-Two Interactive, Ubisoft, and Warner Bros. Interactive Entertainment.

Statements about these new policies were first shared with Kotaku from Sony, Microsoft, and Nintendo. You can read these statements below.

Sony
"Sony Interactive Entertainment aims to ensure PlayStation users have access to information and tools, such as parental wallet controls, that will help them make informed decisions about in-game purchasing. We support industry efforts to disclose the probability of obtaining randomized virtual items, known as loot boxes, and are committed to providing consumers with this information for all games we produce and publish."
Microsoft
"This is why by 2020 all new apps or games offering 'loot boxes' or other mechanisms on Microsoft platforms that provide randomized virtual items for purchase must disclose to customers, prior to purchase, the odds of receiving each item. In addition, we’re proud to offer robust family settings that offer further control over in-game purchasing."
Nintendo
"At Nintendo, ensuring that our customers can make informed choices when they play our games is very important. As part of our ongoing efforts in this area, Nintendo will require disclosure of drop rates in Nintendo Switch games that offer randomized virtual items for purchase, such as loot boxes. This requirement will apply to all new games and includes updates to current games that add loot boxes through in-game purchases.

"We also offer tools like our Nintendo Switch Parental Controls mobile app, which empowers parents to choose what works for their family, including managing in-game purchases and setting playtime limits."
Some companies, such as EA, already started to show odds on loot boxes in games like FIFA 19 with their FIFA 19 Ultimate Team.