Dive Brief:

• In the new year, Amazon and Walmart will have strong competition in cashier-free checkout as Kroger expands its successful "Scan Bag Go" pilot to 400 stores.

• It's not a new effort for the grocery chain. Some stores have had the technology for five years, and more test stores have been added since, for a total of 25 this year, according to Kroger's October presentation to its investors.

• The expansion comes amid Kroger's broader "Restock Kroger" effort, which also includes more personalization, more channels for discovery (including its "Clicklist" online order service), focus on the grocery chain's private label brands and a commitment to price competition.

Dive Insight:

Now that Whole Foods is an Amazon joint, many are watching and waiting to see how head-to-head competition plays out between Amazon and Walmart on the grocery front. (The retail giant already gets half of its sales from its grocery sections, which are a big draw that boost non-food sales.) But both must also contend with Kroger.

The grocery chain took a hit from investors earlier this year when it trumpeted its "price investment" plan — a circuitous way of saying it would be slashing prices. Walmart, Amazon and Target answered that with price cuts of their own, as low-priced grocers Aldi, Trader Joe's and Lidl continue to expand across the U.S.

Many fear an emerging price war that could pound the already thin margins in the sector. In any case, Kroger executives continue to promise that the company will not be beaten on price.

Kroger is no slouch when it comes to technology, either, with its "84.51" analytics arm helping the company pinpoint who comes through its doors and when, and to determine optimal pricing, among other crucial data points. 

The grocer also has a formidable private label assortment — 30,000-plus SKUs and a record 8.2 billion units sold in 2016, according to Progressive Grocer — an area that has been getting Amazon a lot of attention, especially since its purchase of Whole Foods and that unit's strong store brands.

But Kroger's Scan Bag Go stores represent a tech-based convenience play that may surprise many observers who expected such advancements to come out of Amazon or Walmart. Walmart's subsidiary Code Eight, for example, is reportedly developing a technology-heavy store that uses computer vision and cashier-free checkout, led by Mike Hanrahan, Jet co-founder and former chief technology officer. Store No. 8 principal Katie Finnegan told Retail Dive in October that the company thinks about technologies in three-, five-, seven- and even 10-year increments. Walmart's more fully developed Scan & Go checkout is now in place at about dozen stores in several states.

Meanwhile, Walmart partner JD.com in China is planning "hundreds" of unmanned convenience stores using facial recognition technology that allows customers to pay without standing in a checkout line. The much-touted Amazon Go store, meanwhile, remains open only to Amazon employees, with technical snafus still reportedly being ironed out. 

In fact, Kroger appears to be much farther along than both of them. Neither Walmart nor Amazon is touching Kroger's 400-store effort slated for next year. "Everything we're seeing in our data and in customer behavior tells us Kroger's transition to seamless is working," Kroger CEO Rodney McMullen told analysts last month, according to a transcript from Seeking Alpha.

"Today households that engage in our seamless offerings, engaging digitally and with our physical stores spend more per week than households that do not," McMullen said. "The future looks even more promising. We'll continue to add even more services, expand our available product selection and more effectively use our insights to create a personalized experience that every customer will love."