By Suzanne Vranica

CANNES, France — American corporations are tiptoeing toward a future powered by artificial intelligence. Madison Avenue is already all in.

From launching and monitoring campaigns to crafting creative messages, advertising agencies and brands are increasingly integrating AI into every part of the ad business.

That shift was on full display during the Cannes Lions ad festival, where rosé-fueled conversations about the technology were filled with a mix of excitement and dread. Pinterest showed off a new tool that automatically selects the ad most likely to perform best, while TikTok played matchmaker for brands and creators and debuted tools to generate ads on the fly. Meanwhile, OpenAI courted brands and agencies to bolster its nascent ad business.

If Mad Men-esque creatives defined the last era of advertising, AI-powered campaigns and digital-native creators, who dominated the action along the Croisette, are now the industry's lifeblood. Many of the ads consumers already see have been shaped in some way by generative AI, a trend likely to accelerate.

At Hershey, AI tools have cut ad production time from over six weeks down to hours or minutes, saving the company several million dollars annually on digital ad production costs, said Vinny Rinaldi, Hershey's vice president of consumer connections. AI tools measure the impact marketing has on sales in one month, a process that previously took 20 weeks.

Mortgage giant Rocket uses AI to prototype scripts and billboard concepts and to generate text-based digital ads. Rocket CMO Jonathan Mildenhall said that by next year, the ad industry will move past the era of "AI slop" and gain the sophistication needed to deploy long-form, AI-generated ads.

The embrace of AI in advertising has been a boon to big tech companies like Alphabet's Google and Meta Platforms. AI is improving ad targeting and recommendation systems, which keep users on the apps longer, while forcing agencies to restructure and invest in new technologies.

Google, Meta and Amazon currently control about 58% of U.S. ad revenue, a figure projected to hit 63% by 2030, according to industry advisory firm Madison and Wall.

Those companies' AI offerings and expertise "means they can produce the outcomes that marketers want more efficiently than other companies can," said Brian Wieser, founder of Madison and Wall.

AI is now so embedded in the industry that Cannes Lions requires award entrants to describe how the technology was used in their ads or buying plans.

"Would you have tried to put your finger in the dam of digital when digital was disrupting everything? The industry has to embrace it," said Philip Thomas, chairman of Cannes Lions.

OpenAI showcased its Codex enterprise product in meetings with ad agencies and creators at this year's event, highlighting how it could assist with creative production. It offered festival attendees AI-generated selfies with a digital replica of CEO Sam Altman.

Company executives hosted dinners, discussions and cocktail parties throughout the week to court top brands as the company tries to supercharge its recently launched ad business. Its ChatGPT ad pilot is now live in seven markets including the U.S., Canada, U.K. and Japan.

AI's growing role in companies' marketing programs is expected to be painful for ad agencies. AI can automate content creation and media planning in seconds, leading brands to pressure agencies to cut prices for work they know can now be generated faster and cheaper. AI tools will also allow some advertisers to bring creative production in-house.

London-based WPP is in the midst of a major restructuring partly to adapt to the operational difficulties brought on by AI. The firm plans to cut hundreds of jobs in the coming months after slashing nearly 10,000 positions last year, according to a person familiar with the matter.

Investors remain cautious about how well the large holding companies can pivot to the AI economy. Despite outperforming rivals in winning new business and organic revenue growth, Publicis stock is down about 2% over the past year.

At a presentation attended by hundreds of advertisers and dozens of investors, Publicis showcased how the firm helped clients like Coca-Cola and candy maker Mars with their marketing AI transformations.

Publishers, meanwhile, are grappling with how to remain visible — and generate ad dollars — as a link-heavy search experience that drove traffic is being replaced by chatbot-driven search featuring AI-generated summaries.

Although still in its infancy, generative search ad revenue is expected to reach $5.1 billion globally this year and surpass $101 billion by 2030, according to projections from ad-buying giant WPP Media.

Brands are currently testing ads on platforms like ChatGPT, partly using experimental budgets, said Kate Scott-Dawkins, WPP Media's global president of business intelligence. She doesn't expect any decline in traditional search ad revenue until 2029.

Write to Suzanne Vranica at Suzanne.Vranica@wsj.com