Cisco agreed on Thursday to buy Splunk, a data-analysis software company, for $28 billion in cash, as technology giants continue to look to acquisitions as a way to grow — particularly in hot sectors like artificial intelligence.

The deal is the largest ever announced by Cisco, a longtime buyer of smaller tech companies, and suggests the company is willing to test antitrust officials’ growing opposition to big-ticket mergers and acquisitions.

Founded in 2003, Splunk — whose name refers to spelunking, or cave exploration — focuses on mining its customers’ data for insights, particularly on security vulnerabilities and other trends in their business. This summer, Splunk announced a flurry of A.I.-infused services meant to help companies detect and respond to potential issues more quickly.

Cisco said it planned to combine Splunk’s capabilities with its own security offerings, including the monitoring of customers’ network data, web traffic and emails.

“I consistently heard from our customers the strategic importance of what Splunk does,” Chuck Robbins, the Cisco chief executive, said in an interview. Combining Splunk’s systems with the information collected from Cisco’s, he said, presented an “opportunity to bring a level of insight that’s unmatched.”

Gary Steele, the Splunk chief executive, added that Cisco’s bigger sales footprint would help his company sell its products more widely, especially internationally. Mr. Steele is set to stay on as a member of Cisco’s leadership team when the transaction closes, which is expected by the fall of next year.

The deal moves Cisco further away from its roots in network hardware and into higher-margin, more predictable software subscriptions.

Much of Cisco’s push into software is being driven by acquisitions: The company has announced eight takeovers this year, according to S&P Capital IQ.

By some measures, Cisco is paying a high price. The transaction valued Splunk at $157 a share, a 31 percent premium to where its stock closed on Wednesday and 25 percent above the company’s 52-week high. (Cisco had held discussions to buy Splunk early last year.)

Shares in Cisco fell 4 percent after the deal was announced. Shares in Splunk rose on the news, but still traded below the acquisition offer price, suggesting investors were somewhat skeptical that the deal would be completed. Among the potential concerns is whether antitrust regulators will approve the transaction, given increased scrutiny of big mergers by the Biden administration.

Privately, corporate executives have said recent setbacks for regulators, including defeats for the Federal Trade Commission’s effort to block Microsoft’s $70 billion takeover of Activision Blizzard, could make it easier to do deals.

Mr. Robbins expressed confidence in the Cisco-Splunk deal’s clearing antitrust hurdles, because there is little overlap in the companies’ products.