Magnite is a US company, listed on Nasdaq as MGNI, that runs a sell-side platform (SSP): software through which publishers, streaming services and app developers offer advertising space to many automated buyers at once. The category exists because a publisher cannot sensibly build a separate connection to every advertiser, agency and bidding system. In its annual report for 2025, Magnite calls itself "the world's largest independent omni-channel sell-side advertising platform". The word "independent" has a specific meaning there: the company owns no media properties and offers no demand-side platform (DSP), the buyer-side software that bids for impressions, which it presents as protection against conflicts of interest.

How an impression moves through Magnite

An ad request begins when a viewer opens a page, an app or an ad break in a stream. The SSP packages that impression as an OpenRTB bid request, using the IAB Tech Lab's real-time bidding protocol, with fields such as the floor price (bidfloor), private-marketplace deal IDs and the SupplyChain object listing intermediaries. Buyers cap the number of queries per second they accept, so the SSP forwards each DSP only the requests it is likely to bid on, a practice known as traffic shaping. Bids below the floor are discarded, a winner is chosen, the creative returns to the publisher's ad server, and the SSP's fee is deducted before the publisher is paid.

On websites, the usual entry point is header bidding, in which a wrapper such as Prebid.js offers an impression to several exchanges before the ad server decides. According to Prebid's documentation, publishers configure the bidder "magnite" with three required integer parameters - accountId, siteId and zoneId - and the adapter handles banner, instream and outstream video, and native formats. It replaces an older adapter named "rubicon", which can be aliased so that existing ad server line items keep working. The documentation lists no Prebid Server version.

Revenue follows volume. According to the annual report, Magnite generally earns a percentage of advertising spend, which it calls its take rate. For some clients, notably for ad serving, it charges a fixed CPM (cost per thousand impressions), and it may also collect fixed monthly fees. Publisher ad operations teams set floors, blocklists and deals in the platform, while agencies and trading desks typically arrive through DSP seats.

Products around the exchange

Three products widen the exchange. Demand Manager handles Prebid-based wrappers; when CairoRCS Media, an Italian group, adopted it on July 10, 2024, the features included machine-learning A/B tests of configurations and "microwrappers" meant to lighten page loads. SpringServe is a connected TV (CTV) ad server founded in New York in 2015; according to ExchangeWire, Magnite announced its purchase on July 1, 2021 for about $31m. In October 2025 Magnite introduced machine-learning ad podding, where a pod is a group of ads in one break. The system predicts how many bid requests each break needs, applies competitive separation and frequency caps, and is designed for OpenRTB 2.6, the version with native multi-ad support.

ClearLine, in an evolved version announced October 1, 2025, combines curation (packaging inventory and data into deals) with activation, and runs on the same infrastructure as SpringServe. Closed-beta partners included Disney Advertising, LG Ad Solutions, Paramount, Roku, Samsung and Warner Bros. Discovery.

From Rubicon Project to Magnite

Rubicon Project was founded in Los Angeles on May 1, 2007, according to the company's Wikipedia entry, and listed in April 2014. On September 11, 2017, Rubicon, AppNexus and PubMatic spun Prebid into the independent Prebid.org. Then, on January 22, 2018, Rubicon began choosing header-bidding winners on a first-price basis, giving bidders an Estimated Market Rate feature to lower bids while keeping win rates high. Waterfall and private-marketplace transactions stayed on a modified second-price auction.

Consolidation followed. The merger with Telaria, a CTV video specialist, was announced on December 19, 2019 and completed on April 1, 2020, with each Telaria share converting into 1.082 Rubicon shares, according to Magnite's release. The combined company took the Magnite name and ticker on July 1, 2020, with Michael Barrett as chief executive. SpotX came next. Announced in February 2021 at $1.17bn, the purchase from RTL Group closed in early May at a final price of about $1.14bn, made up of $640m in cash and 12,374,315 shares, according to Advanced Television.

Streaming partnerships then shaped the business. Magnite said on May 22, 2024 that Netflix ads would be bought through DSPs from that summer, starting with Google DV360 and The Trade Desk, and delivered through Magnite's platform alongside Netflix's in-house ad server. On October 23, 2024, Disney renewed its partnership for two more years, six in total, adding six Latin American markets; more than 30 DSPs transact with Disney through Magnite.

Why the company matters to marketers

For streaming, Magnite is a main route to premium inventory. It cites a March 2025 Jounce Media analysis putting its CTV supply coverage at 99%, though coverage measures the reach of supply rather than the share of spend. Scale shows in the results. In the second quarter of 2026, revenue was $192.8m, up 11%, while contribution ex-TAC - revenue less traffic acquisition costs, the sums passed to publishers - rose 17% to $189.6m. CTV contributed $97.1m, up 36%. In the first quarter, CTV passed half of the total for the first time, at 51% against 43% a year earlier.

Deal IDs, curated packages and, increasingly, software agents all run through this plumbing. Decisions on floors, fees and data handling at an SSP therefore shape what buyers can see and what they pay.

Limitations, criticisms and open disputes

Concentration is the first issue. The annual report says two buyers indirectly contributed about 44% of 2025 revenue, a small number of sellers supply a large share of CTV audiences, and spend sits with relatively few DSPs. Segment balance is the second. Display, video and audio (DV+) contribution fell 5% in the first quarter of 2026, with the chief financial officer citing automotive weakness, before growing 2% in the second.

The third is dependence on Google's stack. Magnite's filing estimates that about 90% of open-web publishers use Google's ad server, and in May 2025 executives estimated that Google's exchange held over 60% of the DV+ market, against a mid-single-digit share for Magnite. Magnite sued Google on September 16, 2025 in the Eastern District of Virginia, seeking treble damages. It alleges that First Look let Google's exchange intercept impressions and that Project Poirot reduced DV360 bids on rival exchanges. Last look, a related practice, let Google's exchange see the highest rival bid before bidding again. These are allegations in a pending suit, and Google has said it will appeal the April 17, 2025 liability findings.

The fourth is neutrality in agentic buying. Magnite describes Orchestration as open, yet it also runs the coordination layer, its own Seller Agent and its own Buyer Agent, and in a French test its buyer agent transacted with its seller agent. The second-quarter filing did not break out agentic revenue.

Not the same as

Rubicon Project is Magnite's former name; "rubicon" survives as the label of the older Prebid adapter. SpringServe is the ad server that decides what plays in a break, whereas the exchange auctions impressions, and Magnite owns both. A DSP serves advertisers and does the bidding; Magnite has none. Google Ad Manager bundles DoubleClick for Publishers (DFP), the ad server, with AdX, the exchange, making it a rival in display and the defendant above. PubMatic and Index Exchange are competing SSPs, not subsidiaries.

Recent developments

On September 2, 2026, Judge Leonie Brinkema rejected the government's request to force a sale of AdX and accepted most proposed behavioural remedies. The resulting decree would run six years and require a Prebid interface to AdX and DFP, pending entry of a final judgment. Magnite appears only in a list of private suits. On September 17, as the full ruling was unsealed, Magnite shares rose as much as 12.9% intraday, according to Motley Fool, and StoneX lifted its price target to $43 from $33. A joint proposed final judgment filed October 2 still carried rival wording: six months from the government, 12 from Google, for AdX to accept bids from non-Google ad servers. Magnite's guidance excludes any share gains. Barrett had said on the first-quarter call, "I completely anticipate a favorable ruling for us and impact in 2026".

The agentic push continues. Magnite announced a seller agent inside SpringServe on January 6, 2026, after a December test with Scope3 as buyer agent. A buyer agent followed on April 27, tested by Kepler and MiQ on Disney inventory. Orchestration launched in beta on June 11 with dentsu and DIRECTV Advertising. Barrett told tipsheet.ai in July that the most optimistic forecasts put agentic spend at $600m to $700m in 2027, which he called modest. PubMatic builds its story around AI while Magnite treats it mainly as an efficiency tool. Brian Gephart became chief financial officer on October 1, 2026, succeeding David Day, according to Magnite's release.

Timeline

  • May 1, 2007: Rubicon Project is founded in Los Angeles
  • April 2014: Rubicon Project lists on the stock market
  • September 11, 2017: Rubicon, AppNexus and PubMatic spin Prebid into Prebid.org
  • January 22, 2018: Rubicon moves header bidding to first-price auctions
  • December 19, 2019: Rubicon Project and Telaria announce their merger
  • April 1, 2020: The merger closes
  • July 1, 2020: The combined company becomes Magnite, trading as MGNI
  • February 5, 2021: Magnite agrees to buy SpotX for $1.17bn
  • Early May 2021: The SpotX purchase closes at about $1.14bn
  • July 1, 2021: Magnite announces the purchase of SpringServe for about $31m
  • May 22, 2024: Magnite details its role in Netflix's programmatic advertising
  • October 23, 2024: Disney extends its Magnite partnership by two years
  • April 17, 2025: A federal court finds Google monopolised ad server and exchange markets
  • September 9, 2025: Magnite acquires streamr.ai
  • September 16, 2025: Magnite sues Google
  • October 1, 2025: Magnite announces an evolved ClearLine
  • January 6, 2026: Magnite discloses its seller agent
  • March 15, 2026: Magnite repays $205.1m of convertible notes at maturity
  • April 27, 2026: Magnite introduces a buyer agent
  • June 11, 2026: Magnite Orchestration opens in beta
  • August 5, 2026: Second-quarter results lift full-year guidance
  • September 2, 2026: Judge Brinkema rejects the AdX divestiture
  • September 16, 2026: Orchestration extends to four inventory categories
  • October 1, 2026: Brian Gephart becomes chief financial officer
  • October 2, 2026: Parties file a proposed final judgment in the Google case

Summary

Who. Magnite, led by chief executive Michael Barrett, serves publishers and streaming services on the sell side and agencies, trading desks and DSPs on the buy side. It competes with PubMatic, Index Exchange and Google's AdX.

What. An independent sell-side platform that auctions ad impressions through OpenRTB and header bidding, backed by the SpringServe CTV ad server, Demand Manager and the ClearLine curation platform.

When. Rubicon Project began in 2007; the Telaria merger closed on April 1, 2020 and the Magnite name arrived on July 1, 2020. As of October 2026, the Google remedies and agentic products are the live issues.

Where. Operations span North America, Australia and Europe, with Asia and South America developing, according to its annual report. Transactions run on cloud infrastructure for CTV and on-premises data centres for most other traffic.

Why. Publishers need one connection to many buyers, and buyers want premium inventory without separate integrations. Magnite's independence from media ownership and DSPs is its stated answer to conflict-of-interest concerns.