Leading adtech outfits AppNexus, Index Exchange and PubMatic are this week rolling out a server-side header bidding initiative, along with Facebook, in a move that is likely to further drive competition with Google when it comes to publishers’ inventory.

The parties are working cooperatively to rollout PreBid server, a server-to-server header bidding solution for parties working as part of the open source prebid.js project, which will start shipping this week.

This means that any publisher that has PreBid.js installed on their website can now access the new software that has server-to-server support built in, and then choose which header bidding partners they want to transact with, thus increasing their access to buyer-demand.

Michael Richardson, AppNexus product line manager for marketplace, direct supply, told The Drum: “The major top points are that we are open-sourcing the code behind it, so that people can ensure that it is fully transparent and ensure that it does what it says it does.

"We’re making sure that it is a pure transparent system – one that doesn’t do any decisioning or logic, and is really just to take the basic concepts of header bidding and making them better and faster, which should hopefully improve the user experience.”

Prebid is an open source initiative hosted by AppNexus that is free to publishers with audited domains on the the adtech outfit's platform. The latest update means suitable publishers can select the header bidding demand partner of their choice through a server-side connection, rather than being called directly from the browser.

“I hope that by open sourcing our code it will further demonstrate our commitment to a more transparent internet… Header bidding should be free, should be fair and should be transparent, we don’t want to get into another situation where we have entrenched monopolies that are potentially playing games,” added Richardson, in a veiled reference to Google’s DoubleClick.

He went on to confirm Facebook as a participating partner, which has already begun its operations in the header bidding space, although the social network was unable to respond to The Drum’s request for comment by time of publication.

The move towards header bidding is read by many as a move away from its earlier ‘walled garden’ stance, and perceived as a direct play to compete with Google when it comes to monetizing media inventory outside of Facebook-owned and operated properties. Certain sources have speculated that this could also lead to Facebook consenting to further third-party metrics in a bid to appease advertiser-demand for commonality when it comes to assessing performance.

Effectively, the joint initiative increases the amount of adtech partners that participating publishers can work with to monetize their inventory, as it offers them more options than the allegedly biased Google ‘waterfall’ method of auctioning media.

Drew Bradstock, senior vice president of product at Index Exchange, went on to explain how his company is involved in the initiative: “Index Exchange and AppNexus currently bid into each others’ header bidding offerings via the client-side. With Prebid server and Index header tag wrapper 2.0, we are now expanding that partnership to include server-side integration as well.

He went on to explain how the Prebid server-to-server partnership between AppNexus and Index expands the number of choices publishers have when it comes to header bidding, thus reducing the likelihood that Google’s DoubleClick will win most of the auctions it has until now.

“Ad tech companies that want to remain relevant in the future must cater to the needs of publishers. The theme among the publishers we talk to is choice: between client-side and server-side, between wrapper providers, and between demand sources,” he concluded.

Evan Simeone, PubMatic, SVP of product development, went on to explain how the hybrid approach benefits adtech players, as it allows them to offer both client-side header bidding, as well as integrate into a server-side wrapper which can send an ad request out via an alternative path.

“So this isn’t something where you have to make some big strategic decision and then you’re locked-in forever,” explained Simeone. “Because there are instances and partners that we’re working with that might want to work with client-side and others with server-side, or you may want to migrate from one to another.”