Investment advisory services firm Cambridge Assoc. is close to inking a deal to relocate into more than 100,000 square feet of office space at 125 High St. in Boston, according to industry sources familiar with the move.

The firm will move its headquarters out of 100 Summer St., owned by Equity Office Properties (EOP).

Currently, 100 Summer St. is averaging rents in the mid-$40s per-square-foot range, according to industry executives. Proposals at 125 High St., owned by Tishman Speyer, are starting in the mid-$40s and reaching the mid-$50s range, sources told Banker & Tradesman.  Neither EOP nor Tishman returned calls seeking comment.

The property at 125 High St. totals approximately 1.5 million square feet and encompasses a full city block bounded by High, Oliver, Purchase and Pearl streets. The building was designed by Jung Brannen Assoc. and completed in 1991. With a footprint of 2.5 acres, the complex is composed of two office towers and a renovated 19th century building, all connected by an 11-story glass atrium.