ST. LOUIS – Panera Bread Co., a subsidiary of the JAB Holding Co., has entered into a definitive agreement to acquire Au Bon Pain Holding Co. Inc., parent company of Au Bon Pain. Financial terms of the transaction, which is expected to close during the fourth quarter, were not disclosed.

In a separate announcement, Panera said Ron Shaich, founder, chairman and CEO, will step down as CEO effective Jan. 1, 2018. Shaich will remain chairman of the board and continue to work on strategy, communications and acquisitions for Panera, such as the Au Bon Pain acquisition.

Based in Boston, Au Bon Pain is a fast-casual bakery cafe chain that operates 304 units worldwide. The chain operates in six key trade channels, including urban office buildings, hospitals, universities, transportation centers, malls and museums. Au Bon Pain’s signature items include sandwiches, bread, pastries, salads, soups and coffee.

The acquisition will reunite Au Bon Pain and Panera after the two brands parted ways in 1999. Shaich and his late partner Louis Kane created Au Bon Pain Co. Inc. in 1981. The company went public in 1991 and acquired Saint Louis Bread Co. in 1993. Saint Louis Bread was then renamed Panera Bread and, in 1999, Au Bon Pain was sold so all resources could be focused on Panera, the company said.

“With the acquisition we are announcing today, we are bringing Au Bon Pain and Panera together again,” Shaich said. “This acquisition offers the strategic opportunity for us to grow in several new real estate channels, including hospitals, universities, transportation centers and urban locations, among others.”

Panera Bread was acquired by JAB Holding in July for approximately $7.5 billion. Panera’s acquisition of Au Bon Pain will bring the brand into JAB’s growing global roster of bakery cafe chains that also includes Krispy Kreme Doughnuts, Caribou Coffee, Einstein Noah, Bruegger’s Bagels, Espresso House and Peet’s Coffee and Tea.

Shaich said part of his reasoning for stepping down as CEO is so he may better allocate his time between initiatives for JAB and Panera.

“This is the right time for me to step down as CEO while still staying involved in the business as chairman,” Shaich said. “I returned in 2011 because our growth was slowing, and we needed to reposition Panera as a better competitive alternative with expanded growth opportunities. And I’m happy to say we’ve done just that.”

Blaine Hurst, president of Panera, will succeed Shaich as CEO. Hurst joined the company in January 2011 as senior vice president of technology and transformation. He was promoted to executive vice president of technology and transformation in May 2013 and executive vice president and chief transformation and growth officer in October 2014. Hurst was named president in December 2016.

Before joining Panera, Hurst was vice chairman and president at Papa John’s International Inc. Before that, he was president of restaurant technology solutions at eMac Digital LLC, an enterprise backed by McDonald’s Corp., and vice president of information services at Boston Chicken.

“I’m very excited about the future of Panera,” Hurst said. “The past seven years have given me the opportunity to learn from an industry icon. And I have been fortunate to lead and be a part of many of the initiatives that are now driving Panera’s success. We’ve built a great team — in fact, it’s the best team I know of in the restaurant industry. I’m looking forward to continuing working with them and our partners at JAB as we take Panera forward. With exciting new initiatives underway to better serve our customers and improve their dining experience, I believe our opportunity is even brighter. I thank Ron and JAB for their confidence in me.”