Mosseri also agreed that Facebook is now more of a competitor, saying it's not the main way people find things anymore. He suggested that YouTube might be the most popular way to discover things now, but he thought TikTok would become more popular than YouTube later, based on the information Meta had.

Mosseri suggested that Facebook's most effective competitive approach would be to serve as the primary platform for content discovery, yet he found it noteworthy that TikTok, being solely video-based, was significantly outperforming them. He speculated that TikTok was expanding the mobile social media market while simultaneously encroaching upon traditional television, longer-form video content, and services like Netflix.

Mosseri was proven right. One study found that in 2021, people in the U.S. spent more time watching TikTok than YouTube on average. Another study in 2023 showed that kids aged four to eighteen spent 60% more time on TikTok than YouTube. Last year, TikTok started allowing videos up to 60 minutes long, likely to compete with YouTube.

Earlier this week, Netflix unveiled its own TikTok-style feature within its mobile application, presenting a novel vertical video feed of suggested content, tailored to each individual user's preferences.

However, during the trial, the U.S. government is striving to demonstrate that Meta breached antitrust regulations by acquiring companies such as Instagram and WhatsApp with the intent of establishing a social networking monopoly. A document of this nature could undermine their case, particularly considering that, internally, Meta executives were conversing about the significant challenges Facebook was facing from TikTok.

For example, Zuckerberg pointed out that even if Facebook continued to be the most prominent application regarding daily or weekly user engagement, it had been surpassed in terms of time spent.

He further noted that TikTok facilitates a sense of shared context among its users, implying that individuals with similar interests are likely to encounter comparable content in their feeds.

"This makes it naturally social because instead of sending content to a friend, you can just think they've already seen it," the CEO said. "If we could reach this level with topics and separate content on FB, that would be very good."

Several other executives also interjected their perspectives.

Will Cathcart, Head of WhatsApp, indicated that TikTok users commenting on videos within a specific niche would prompt the algorithm to consistently show those users and other commenters the same videos over time.

Stan Chudnovsky, then a Vice President and General Manager at Meta, indicated that Meta had now entered a competitive landscape that had become highly fragmented, with numerous companies impacting their growth.

He added that just adding a new format, like they did with Stories, is not enough now because there are many other places people can go, mentioning popular social apps in the U.S. such as TikTok, Twitter, iMessage, Snap, YouTube, Reddit, and Discord.

John Hegeman, who was the VP of ads and is now the chief revenue officer, agreed that TikTok was clearly ahead in areas like short videos, how things are ranked, and tools for creating content. However, he said he thought Meta could catch up if creators also posted on Reels.

Nonetheless, he expressed reservations about the extent of Meta's lag in machine learning, technical capabilities, and content creation instruments. The document portrays Facebook, from Meta's perspective, as an underdog within the social media landscape.

This document isn't the only one that has appeared during the trial to show that Meta is worried about competition. Zuckerberg himself said last month that TikTok doing well was a danger to Meta's business and had made it grow more slowly.