AI Firm Sierra Signs 94K-SF Deal at Rockrose’s 11 East 26th Street

By Mark Hallum May 1, 2026 3:52 pm

Henry (left) and Justin Elghanayan of Rockrose Development and 11 E 26th Street. PHOTOS: Courtesy Rockrose Development; Propertyshark

An artificial intelligence firm that provides businesses with customer support is opening offices in Midtown South.

After announcing in May 2025 that it would establish a New York City presence, Sierra has signed a 94,145-square-foot lease at Rockrose Development’s 11 East 26th Street, according to a monthly Manhattan office report from Colliers.

The deal represents Sierra’s second office location in New York City, following its first lease for a 14,563-square-foot office space at 375 West Broadway in SoHo in October.

Spokespeople for Rockrose and Colliers did not immediately respond to requests for details about the length of the lease and the asking rent, but asking rent in the building was $145 per square foot in February, Commercial Observer previously reported.

The San Francisco-based AI firm, which has offices in Atlanta, London, Singapore, Tokyo, Paris, Madrid and Toronto, was founded in 2023 by Bret Taylor and Clay Bavor, according to the company website.

It’s unclear who brokered the deal, but CBRE represented Sierra in its SoHo deal in October.

Rockrose is owned by Henry and Justin Elghanayan, a branch of the same family that owns and operates development firm TF Cornerstone, which notably split away from a multi-generational development firm in 2009 with the help of a good old fashioned coin toss.

Other tenants at the 22-story office building between Madison and Fifth avenues include Activate Consulting, which expanded to 24,144 square feet in February, and lighting manufacturing company Lutron Electronics, which took 12,074 square feet on the entire 21st floor in October 2025.

Sierra’s deal at 11 East 26th Street was one of the largest office leases signed in Manhattan in April, following law firm Cleary Gottlieb Steen & Hamilton’s 475,000-square-foot deal at One Liberty Plaza, health care platform Tennr’s 124,733-square-foot lease at 345 Hudson Street, and trading firm Jump Trading’s 99,305-square-foot deal at 50 Hudson Yards, according to the Colliers report.