Financial Engines is close to a deal to add its online investment advice to Wells Fargo & Co's retirement platform, according to a Wells presentation obtained by Reuters, news that boosted Financial Engine's stock more than 6 percent.

The move would make Financial Engines' service available to the 3.8 million 401(k) participants on Wells' 401(k) record-keeping platform, which is the seventh-largest in the United States, according to the company.

Financial Engines' stock retreated slightly, to $42.50 a share on Nasdaq, still up 4 percent in Thursday afternoon trading.

As of March 31, Sunnyvale, California-based Financial Engines provided online advisory services to 8.9 million 401(k) participants, according to the company. It serves eight of the 10 largest 401(k) record-keepers.

While a deal has not been signed, conversations have been ongoing for several months, according to a source familiar with them who wished to remain anonymous because the discussions were confidential.

Both Wells Fargo and Financial Engines declined to comment.

Financial Engines CEO Larry Raffone told analysts in February that the firm had signed a letter of intent with "a leading provider" of 401(k) plans, but declined to name it. During his firm's first-quarter earnings call in May, Raffone said that letter of intent was still in place.

Financial Engines provides online advice to participants of some of the largest 401(k) plans in the country. It has signed on 146 of the Fortune 500 companies to help their employees, according to the firm.

Wells Fargo, the fourth-largest U.S. bank by assets, also offers online advice through a partnership with Morningstar, the Chicago-based fund research firm, which dates 2003, according to Wells.