What Is the Open Internet?
The open internet refers to the ad-supported web ecosystem outside of closed, proprietary platforms. In digital advertising, it describes the inventory available across independent publishers, news sites, blogs, streaming apps, and connected TV services, accessed programmatically through open auction systems rather than bought directly through a platform’s own interface. It stands in contrast to walled gardens such as Google, Meta, and Amazon, which keep user data and transactions within their own ecosystems.
Open Internet vs. Walled Gardens
Walled gardens collectively account for roughly 65 to 70 percent of digital ad spend in the United States. The remaining 30 to 35 percent flows through the open internet, representing hundreds of billions of impressions served daily across millions of independent publisher domains.
The key structural difference is data portability. On a walled garden, advertisers can target audiences using the platform’s proprietary data, but they cannot export those audiences, match them to external datasets, or observe user behavior once someone leaves the platform. On the open internet, advertisers can apply first-party data segments, third-party audience data, and contextual signals, then measure outcomes across the full customer journey using their own tracking infrastructure.
| Attribute | Walled Garden | Open Internet |
|---|---|---|
| Audience data ownership | Platform controls | Advertiser controls |
| Inventory access | Platform-only | Multi-publisher via DSP |
| Auction transparency | Limited | Bid-level reporting available |
| Creative formats | Platform-specified | IAB standard + custom |
| Attribution methodology | Platform-attributed | Advertiser-defined |
The 30 to 35 percent share flowing through the open internet may look like the smaller slice. It is the only slice where the advertiser controls the data, defines the attribution model, and is not paying a platform tax to reach their own audience.
How Advertising on the Open Internet Works
Open internet advertising runs primarily through programmatic advertising infrastructure. When a user loads a page on an independent publisher, a supply-side platform (SSP) auctions available ad slots in real time. Advertisers bid through a demand-side platform (DSP), and a second-price auction determines the winner in most cases. The entire process completes in under 100 milliseconds, with no human involvement in any individual transaction.
The Basic Auction Formula
In a second-price auction, the winner pays one cent above the second-highest bid rather than their full bid:
Amount Paid = Second-Highest Bid + $0.01
For example, if Advertiser A bids $4.50 CPM and Advertiser B bids $3.80 CPM, Advertiser A wins and pays $3.81 CPM. This structure incentivizes bidders to submit their true valuation rather than strategically underbidding.
Effective CPM Calculation
Buyers on the open internet often evaluate performance using effective CPM (eCPM) to normalize across different buying models:
eCPM = (Total Spend / Total Impressions) x 1,000
A campaign that spends $12,500 and delivers 4.2 million impressions produces an eCPM of $2.98. Benchmarking eCPM against viewability rates, completion rates, and conversion lift gives a fuller picture of inventory quality across open internet buys.
Key Channels Within the Open Internet
The open internet spans several distinct inventory categories, each with its own buying mechanics and audience dynamics.
Display and Native
Standard display inventory on independent publishers remains the largest volume channel. Native ad formats, which match the look and feel of editorial content, typically generate click-through rates two to four times higher than standard display, according to data from ad tech firm Outbrain.
Connected TV (CTV) and Streaming
Streaming services outside the walled garden ecosystem, including Pluto TV, Tubi, and Xumo, sell inventory programmatically through open pipes. Roku reported over 80 million active accounts in 2024, with a significant share of that inventory accessible to open internet buyers through its OneView DSP and external DSP integrations.
Digital Audio
Podcast and streaming audio inventory from independent publishers and networks trades programmatically through platforms such as AdsWizz and Triton Digital. Spotify, while predominantly a walled garden, does open portions of its inventory through programmatic channels.
Digital Out-of-Home (DOOH)
Programmatic DOOH has brought billboard, transit, and retail screen inventory into the open internet buying stack. Buyers can now trigger outdoor placements based on weather data, audience density signals, or dayparting through the same DSP used for display and video.
Why Marketers Use the Open Internet
The open internet delivers specific advantages that walled gardens cannot offer by design. For brands that have built first-party data infrastructure, those advantages concentrate around reach extension, retargeting efficiency, and audience sovereignty.
- Incremental reach: Users who do not engage with Meta or Google properties can be reached across the open web, reducing overlap waste in a broad-reach campaign.
- First-party data activation: CRM lists and site visitor segments can be onboarded to a DSP and matched to open internet inventory without surrendering the data to a platform intermediary.
- Contextual targeting: With third-party cookies phasing out across major browsers, contextual signals derived from page content allow precise targeting without individual user tracking.
- Transparent auction data: Bid-stream data from open internet buys provides competitive intelligence, floor price patterns, and win-rate analysis unavailable in walled garden environments.
Brand Safety and Quality Considerations
The openness that makes open internet inventory flexible also introduces quality risk. Ad fraud, brand safety violations, and low-viewability placements are more common outside curated walled garden environments. Industry estimates from the Association of National Advertisers put ad fraud losses across the digital ecosystem at approximately $120 billion globally in 2023, with the open web accounting for a disproportionate share.
The practical response is to treat open internet supply less like a single channel and more like a supply chain that needs quality controls at every stage. Advertisers typically address this through a layered approach:
- Inclusion and exclusion lists at the domain and app level
- Third-party verification from providers such as IAS (Integral Ad Science) or DoubleVerify
- Private marketplace (PMP) deals with vetted publishers
- Programmatic guaranteed buys that lock in inventory from specific properties
The Open Internet and Identity
As cookies deprecate, the open internet is developing alternative identity solutions to maintain addressability. The Trade Desk’s Unified ID 2.0 (UID2) uses hashed and encrypted email addresses to create a shared identity layer across publishers and advertisers without relying on third-party cookies. LiveRamp’s RampID offers a similar function. Both solutions require publisher and advertiser adoption to work, which is why coverage varies considerably across the open internet ecosystem. Until adoption approaches universality, identity resolution on the open internet will remain uneven.
Peer39 and Oracle’s Contextual Intelligence have made contextual targeting a viable complement to identity-based solutions across real-time bidding environments. The approach works regardless of whether a user is identifiable, making it a reliable fallback for any open internet strategy as cookie deprecation continues.
Measuring Open Internet Performance
Standard metrics for open internet campaigns include viewability rate, video completion rate, and click-through rate. The IAB defines a display ad as viewable when 50 percent of its pixels are in view for at least one second. More sophisticated buyers layer in attention metrics from vendors such as Adelaide and Amplified Intelligence, which score placements based on eye-tracking panel data and proxy signals rather than simple viewability thresholds.
The open internet’s measurement advantage over walled gardens comes down to control. Advertisers can track the full post-click journey using their own pixels, CDPs, and measurement vendors. That means the attribution model belongs to the advertiser, not the platform. On a walled garden, the platform decides what counts as a conversion. On the open internet, the advertiser does.
Frequently Asked Questions
What is the open internet in digital advertising?
The open internet is the ad-supported web ecosystem outside of closed platforms such as Google, Meta, and Amazon. It includes inventory sold across independent publishers, news sites, streaming apps, and connected TV services, bought programmatically through open auction systems rather than through a platform’s proprietary interface.
What is the difference between the open internet and walled gardens?
The core difference is data control. Walled gardens keep audience data, transactions, and attribution within their own systems. The open internet gives advertisers ownership of their data, the ability to apply first-party audiences across publishers, and the ability to measure outcomes using their own tracking tools rather than the platform’s.
How does buying inventory on the open internet work?
Open internet advertising runs through programmatic infrastructure. When a user loads a page on an independent publisher, a supply-side platform (SSP) auctions available ad slots in real time. Advertisers bid through a demand-side platform (DSP), and the auction clears in under 100 milliseconds using a second-price model in most cases.
Is the open internet safe for brands to advertise on?
Brand safety on the open internet requires active management. Unlike walled gardens, which control their inventory environment, the open web spans millions of publisher domains with varying content standards. Advertisers typically use domain inclusion and exclusion lists, third-party verification from providers like IAS or DoubleVerify, and private marketplace deals with vetted publishers to manage exposure.
What is replacing third-party cookies on the open internet?
Two approaches are emerging. Email-based identity solutions, including The Trade Desk’s Unified ID 2.0 (UID2) and LiveRamp’s RampID, use hashed email addresses to maintain audience addressability without cookies. Contextual targeting platforms like Peer39 allow precise targeting based on page content rather than individual user identity, and require no identity resolution at all.
How do you measure open internet campaign performance?
Standard metrics include viewability rate, video completion rate, and click-through rate. More advanced buyers add attention metrics from vendors like Adelaide and Amplified Intelligence, which score placements using eye-tracking data rather than viewability thresholds alone. The key measurement advantage of the open internet is that advertisers can track the full post-click journey using their own analytics infrastructure, independent of any platform.