CEOs from Apple, Amazon, Google, and Facebook had to defend their companies against what lawmakers called 'a pattern of' monopolistic behavior. Here's how each was grilled during Wednesday's landmark hearing.

• Wednesday's tech antitrust hearing was a grueling six-hour event in which House committee members grilled Jeff Bezos, Tim Cook, Mark Zuckerberg, and Sundar Pichai about their companies' market power.
• Cook, Apple's CEO, received what seemed like the fewest questions, but he was asked about the App Store and how Apple treats app developers.
• Zuckerberg was probed on Facebook's acquisition strategy and whether it bought companies like Instagram to "neutralize" a competitor.
• Pichai, who is CEO of Google-parent Alphabet, received what seemed like the most questions from the committee on matters ranging from perceived conservative censorship to Google's search dominance.
• Bezos had perhaps the most surprising admission of the day when he admitted Amazon may have violated its own policies when it comes to third-party seller data and its private-label business.

Four of tech's most high-profile leaders spend nearly six hours on Wednesday being grilled before the House Judiciary Committee's antitrust subcommittee.

The hearing allowed subcommittee chair Rep. David Cicilline to compel Amazon CEO Jeff Bezos, Apple CEO Tim Cook, Facebook CEO Mark Zuckerberg, and Sundar Pichai, CEO of Google and Alphabet, to answer questions on their companies' acquisition strategies, data collection tactics, advertising methods, and behavior toward consumers and third-party vendors that use their platforms.

The hearing also opened up the floor to questions unrelated to antitrust. Several members of the committee grilled executives like Zuckerberg and Pichai over what they see as conservative censorship on their platforms, and Cook and Bezos were questioned on topics like cancel culture and charitable donations through their platforms.

Wednesday's hearing was the first time Bezos testified before Congress and the first time all four major tech CEOs testified alongside each other. The subcommittee said it would use the testimonies it gathered Wednesday to complete its year-long investigation into whether Apple, Amazon, Facebook, and Google engaged in anticompetitive practices.

But if you didn't sit through all six hours of testimony, here's what you need to know about how each CEO was questioned Wednesday's hearing.

Tim Cook was scrutinized over Apple's treatment of app developers

Cook was largely left alone for a significant portion of the hearing. When he was questioned, Cook was mostly asked about the App Store, and whether Apple applies rules differently to different developers.

Rep. Hank Johnson, a Democrat from Georgia, told Cook the committee's investigation had found that "the rules are made up as you go, they are arbitrarily interpreted and enforced, and are subject to change whenever Apple sees fit to change."

Cook denied that's the case, saying the company treats every developer the same.

"We have open and transparent rules, it's a rigorous process," Cook said. "Because we care so deeply about privacy and security and quality we do look at every app before it goes on. But those rules apply evenly to everyone."

When Johnson asked whether Apple would ever raise App Store commission fees, Cook replied that doing so would push developers to other app stores.

"It's so competitive I would describe it as a street fight for market share," Cook said.

Cook also denied assertions that the company would retaliate against developers who complained about Apple's policies, saying that "it's strongly against our company culture" to bully or retaliate against people.

Mark Zuckerberg was pushed on Facebook's acquisition tactics and its treatment of rivals

Zuckerberg, along with Pichai, seemed to face the brunt of the committee's questioning.

Lawmakers devoted a significant amount of time to how Facebook treats rivals in the social media space. Rep. Pramila Jayapal questioned Zuckerberg on whether the company's competitive strategy includes outright copying features from rivals, and Zuckerberg admitted that Facebook has "certainly adapted features" from other companies.

Lawmakers also grilled Zuckerberg on whether Facebook had ever threatened to clone a rival's product in an attempt to acquire it, like in the case of Snapchat and Instagram, and whether he saw the acquisition as a means to "neutralize" a competitor, which Zuckerberg denied.

"It was clear that this was a space that we were going to compete in one way or another," Zuckerberg said about Instagram. "I don't view those conversations as a threat in any way."

Elsewhere in the hearing, Zuckerberg addressed what some lawmakers viewed as conservative censorship on the platform. Zuckerberg defended Facebook's content moderation policies and said he would investigate complaints of bias among moderators.

"We want to make sure that anything we do reflects the values of the company that we'll give everyone a voice," Zuckerberg said.

Sundar Pichai faced accusations that Google abuses its search prowess to identify competition and crush it

Like Facebook, Pichai had to defend Google over assertions from GOP lawmakers that its platform is inherently biased against conservatives, that it actively attempted to help Hillary Clinton get elected in 2016, and that it's censoring information about an unproven treatment for the coronavirus a malaria drug called hydroxychloroquine. Rep. Mary Gay Scanlon, Democrat of Pennsylvania, described several of these notions as "fringe conspiracy theories."

But Pichai faced a tougher line of questioning when it came to Google's power over its competitors — Cicilline pointed to Yelp, specifically, as a competitor that Google has wielded unfair power over by threatening to delist Yelp in search results.

Cicilline questioned Pichai over what the committee sees as a conflict of interest: that Google search results will frequently point users to other Google products, like YouTube, over competitors. Pichai denied that search results favor Google products.

"We have always focused on providing users with the most relevant information," Pichai said.

Pichai was also questioned over Google's relationship with China — he initially told the committee he didn't have "first-hand knowledge" of China stealing information from Google, though it was one of the main reasons Google pulled out of China. (Pichai later corrected this statement.)

Jeff Bezos was grilled on Amazon's relationship with third-party sellers

Bezos wasn't questioned for a significant portion of the hearing after what was likely a technical issue.

But lawmakers quickly piled on the questions for Bezos on multiple aspects of the company's business, particularly its relationship with third-party sellers. In perhaps the most revelatory moment of the hearing, Bezos told the committee that he couldn't guarantee Amazon had never violated its own policies when it comes using trend data about third-party sellers to dictate Amazon's private-label products.

Amazon was accused of using its size to bully and harass third-party vendors, and that sellers have no other choice but to work with Amazon because "it's the only game in town," according to Cicilline.

Bezos didn't deny that that type of behavior had taken place, but stopped short of admitting any wrongdoing on Amazon's part.

"It does not seem like the correct way to treat her," Bezos said about comments from a third-party seller who said she'd been crushed by Amazon. "I don't understand what's going on in that anecdote. I do not think that's systematically what's going on."