Howard Milstein is no longer thinking about tearing down 335 Madison Ave. but will pour $100 million into a renovation by SHoP Architects.

Son Michael Milstein’s tech hub, Grand Central Tech, is doing so well it is also expanding from 100,000 square feet to 250,0000 square feet. The hub nurtures certain startups with free incubator space while its Urban Tech Hub tenants get below market rents.

The 1.1 million square-foot office tower backs onto Vanderbilt Ave. and is connected to Grand Central Terminal. The generally 40,000 square foot floors surround a dramatic glass atrium.

Renovations include enlarging and creating a new entrance lobby and modernizing the lower façade. They will also add an astounding 150,000 square feet of retail and amenities geared toward the tenants.

“We are incredibly excited about this project, as it as an opportunity to totally reimagine what an office building should be in the 21st century,” said Howard Milstein.

Through Circle Ventures, Milstein Properties has invested in tech firms including Honest Buildings and Common.