Leading Adtech Stock Dumped by Major Backer, According to Recent Filing

On October 31, 2025, Maestria Partners LLC disclosed in a U.S. Securities and Exchange Commission filing that it sold 293,146 Magnite (NASDAQ:MGNI)shares, an estimated $6.92 million transaction for the period ended September 30, 2025.

What Happened

According to a filing with the SEC dated October 31, 2025, Maestria Partners LLC reduced its stake in Magnite by selling approximately 293,000 shares. The estimated value of the shares sold was $6.92 million, based on average pricing for the period. Following the sale, the fund reported holding about 1.14 million shares at period end, valued at $24.85 million as of Q3 2025.

What Else to Know

This was a partial reduction in Magnite, which now represents 7.86% of Maestria’s $316.35 million U.S. equity portfolio.

Top holdings after the filing:

• BN: $36.81 million (11.6% of AUM)
• AMZN: $30.78 million (9.7% of AUM)
• APO: $30.51 million (9.6% of AUM)
• FOUR: $28.83 million (9.1% of AUM)
• GOOGL: $26.63 million (8.4% of AUM)

As of October 30, 2025, shares were priced at $17.31, up 36.19% over the year; shares have outperformed the S&P 500 by 21.30 percentage points over the past year.

Company Overview

Company Snapshot

Magnite, Inc. operates at scale as a leading sell-side advertising technology provider, enabling publishers to monetize digital inventory across multiple channels. The company leverages a robust platform to connect supply and demand in the digital advertising ecosystem, focusing on high-growth segments like connected TV.

The company provides an independent sell-side advertising platform for publishers of digital media, including connected TV (CTV) channels, apps, and websites. It generates revenue primarily by facilitating and optimizing digital advertising transactions between media sellers and buyers through its technology platform.

Magnite serves publishers, advertisers, agencies, agency trading desks, and demand side platforms across the U.S. and international markets.

Foolish Take

Maestria Partners' recent sale of $6.9 million worth of Magnite stock is a move with mixed messages behind it. Here's why.

First, shares of Magnite, a leading provider of sell-side advertising technology, have performed well over the past few years. Indeed, over the last three years, Magnite shares are up 141%, equating to a compound annual growth rate (CAGR) of 34.2%. The S&P 500, on the other hand, has generated a total return of 85% over this same period, with a CAGR of 22.9%. What's more, during the third quarter of 2025, Magnite shares hit a new 52-week high of $26.52.

This performance history suggests that Maestria's sale might be profit taking, but there is another angle to consider.

Google is one of Magnite's biggest competitors, and since the recent antitrust ruling in favor of Google-parent Alphabet, shares of Magnite have plummeted. Magnite stock is down roughly 33% since the start of September, when the ruling in the Alphabet antitrust case was announced.

Therefore, it's possible that Maestria's sale came after the ruling, which could indicate a shift in sentiment.

At any rate, average investors should exercise caution with Magnite stock, given its heightened volatility in the wake of the Alphabet antitrust ruling.

Glossary

13F reportable assets: Securities that institutional investment managers must disclose in quarterly SEC filings if they exceed $100 million in assets.
AUM (Assets Under Management): The total market value of investments managed by a fund or investment firm on behalf of clients.
Partial reduction: Selling only a portion of a fund’s holding in a particular security, rather than the entire position.
Alpha: A measure of an investment’s performance compared to a benchmark, showing value added or subtracted by active management.
Sell-side advertising platform: Technology that helps publishers manage, sell, and optimize their digital advertising inventory to buyers.
Digital inventory: The available ad space on digital media, such as websites, apps, or connected TV channels, that can be sold to advertisers.
Connected TV (CTV): Televisions connected to the internet, allowing streaming of digital content and targeted advertising.
Agency trading desk: Specialized teams within advertising agencies that use technology to buy and manage digital advertising campaigns for clients.
Demand side platform (DSP): Software that enables advertisers and agencies to automate the purchase of digital advertising across multiple sources.
Supply and demand in the digital advertising ecosystem: The interaction between publishers offering ad space (supply) and advertisers seeking to buy it (demand) via technology platforms.
Top holdings: The largest investments or positions held by a fund, typically ranked by market value or portfolio percentage.
TTM: The 12-month period ending with the most recent quarterly report.

Jake Lerch has positions in Alphabet and Amazon. The Motley Fool has positions in and recommends Alphabet, Amazon, Brookfield, Brookfield Corporation, and Shift4 Payments. The Motley Fool recommends Magnite. The Motley Fool has a disclosure policy.