Office Space for Lease in Flatiron District

Flatiron is where the AI money is going. Not the only place, but the loudest one. For two years now the fastest-growing software and AI companies in New York have been planting their flags between Union Square and Madison Square Park, and in Q1 2026 it stopped being a trend and became the whole story. Savills came out and called Midtown South the city’s AI hub, and the engine driving that label sits right here in Flatiron and along Park Avenue South (Savills, Q1 2026 Manhattan Office Market Report, April 2026).

Here is the part the headlines skip. Flatiron is really two markets wearing one name. Up on Park Avenue South and around Madison Square Park, AI and fintech tenants are signing from $90 to $120/SF and buildings are hitting 100% leased. Three blocks west, on the Sixth Avenue side and the prewar side streets, there is still real loft space at real prices for a growing company that does not need to make a statement. Where you land in these dozen blocks matters far more than the fact that you landed in Flatiron, the highest-profile submarket in Midtown South.

Flatiron District Office Market Overview

Here is the mistake almost everyone makes with Flatiron: they shop it like one market. It is not. It is a trophy AI corridor and a value loft district sharing a few blocks, and the deal at One Madison Avenue has nothing to do with the deal in a prewar side-street loft off Sixth. Figure out which one you are shopping before you tour anything, or you will burn a month on buildings that were never going to work.

The backdrop is loud. Midtown South posted 3.0 million SF of leasing in Q1 2026, its strongest first quarter since the third quarter of 2019, and availability dropped 90 basis points to 16.9%, the lowest since the fourth quarter of 2020 (Newmark, Manhattan Office Market Report 1Q26, April 15, 2026). The Flatiron and Union Square piece of that ran tighter than the district at 13.9% availability (Newmark, 1Q26). 

Want the proof? Look at who’s signing.

• Ramp, the fintech, expanded to 285,300 SF at 28-40 West 23rd Street, the biggest Midtown South lease of the quarter and the third-largest in all of Manhattan (The Real Deal, April 2026).
• Clay, an AI sales company that just crossed $100 million in revenue, took 163,000 SF at 11 Madison Avenue at $90/SF and filled the building to 100% (Commercial Observer, March 9, 2026).
• Across the street, Harvey AI doubled down at One Madison Avenue and brought that tower to fully leased too (SL Green, March 2026).

When companies growing this fast commit to ten-year leases at the top of the market, you stop arguing with the chart. For the wider pattern, see our breakdown of the largest Manhattan office leases behind the numbers.

Four Forces to Monitor

• AI reset the top of the corridor. AI firms leased more than 600,000 SF across Manhattan in Q1 2026, surpassing the entire 2024 total in a single quarter, and Midtown South is the epicenter (Colliers, via The Real Deal, April 2026). The biggest of those deals, Clay’s 163,000 SF at 11 Madison, landed right here at $90/SF asking (Commercial Observer, March 9, 2026). Every Park Avenue South landlord now points at that number when they sit down to negotiate.
• The good buildings are filling up. 11 Madison Avenue and One Madison Avenue both hit 100% leased in Q1 2026 (SL Green, March 2026). Park Avenue South corridor availability is tight and getting tighter. If you want a renovated full floor on the east side of Flatiron, the window is closing, and the asking rents reflect it.
• The value side still has room. Savills tracks Flatiron and Park Avenue South as separate submarkets, and in late 2025 the Flatiron piece averaged $64.66/SF against $77.50/SF for Park Avenue South (Savills, Q4 2025 Manhattan Office Market Report). Translated: on the Sixth Avenue side and the prewar side streets, there is still loft space that prices well below the AI corridor for the same neighborhood and the same subway. Touring beats averages here.
• Sublet supply keeps shrinking. Manhattan sublet availability fell nearly 30% over the trailing year, the eighth straight quarter of a tightening or stable market (Colliers, Q1 2026). If your plan was a cheap Flatiron sublet, that ship mostly sailed in 2024. A few still trade, but you have to move fast.

How Much Does Flatiron District Office Space Cost?

Short version: it depends entirely on which side of the neighborhood you are standing on. The Midtown South district average was $88.32/SF in Q1 2026 (Newmark, 1Q26), but that blended number is close to useless for Flatiron on its own, because the spread inside these blocks is enormous. One Madison Avenue asks around $120/SF. Clay just paid $90/SF at 11 Madison. Hex, an AI company out of San Francisco, took a full floor at 250 Park Avenue South at $80/SF (Commercial Observer, January 2026). And on the prewar side streets off Sixth, you can still find office space in the $60s.

So before you tour, answer one question, because it changes everything: do you need to be in the AI corridor, or do you just need to be in Flatiron? A venture-backed AI company recruiting talent against OpenAI money, sure, you pay up for Park Avenue South and Madison Square. A profitable services firm or a growing startup that wants the neighborhood and the commute without the trophy bill, you go west and you go side-street. Same Flatiron. Same trains. Very different rent. Not sure how much space you actually need? Run your headcount through our Office Space Calculator before you tour anything.

A Quick Note on Building Classifications

If you have not shopped Midtown South before, one thing to know up front: the Class A, B, C system does not work here the way it does in Midtown or Downtown. Most of Flatiron’s buildings are converted lofts, former warehouses, and turn-of-the-century cast-iron, not purpose-built office towers. So a 1900s loft on Park Avenue South can technically carry a Class B label and still command rent that beats a Class A tower uptown, because the ceiling height, the light, the floor plate, and the address are what tenants actually pay for. Class describes the building. Rent tier describes what tenants pay. Do not get hung up on the letter. Our explainer on what makes a building Class A, B, or C breaks it down.

Park Avenue South and the AI Corridor

Park Avenue South is the story. For a decade this was a solid but unremarkable loft corridor. Then the AI companies arrived, and it repriced. The marquee deals all landed within a few blocks of Madison Square Park across 2025 and early 2026: Clay’s 163,000 SF at 11 Madison Avenue at $90/SF (Commercial Observer, March 9, 2026), Harvey AI’s expansion to roughly 185,000 SF at One Madison Avenue, where asking rents run around $120/SF, Pinterest and Tempus AI taking space at 11 Madison, and a steady stream of smaller AI tenants like Hex at 250 Park Avenue South and EliseAI nearby at 401 Fifth Avenue (Commercial Observer; The Real Deal, 2025 to 2026). The two anchors, 11 Madison and One Madison, are both owned by SL Green and both fully leased as of Q1 2026.

These are full-block trophy and trophy-adjacent buildings with the amenity packages and the addresses AI flagships want. If you need that kind of space, this is a timing problem, not a budget problem, because they are leasing faster than they are emptying. For what actually separates trophy from regular Class A, see our piece on how trophy buildings set themselves apart in NYC. One caveat on geography: 11 Madison and One Madison sit on the Madison Square edge, which the site’s taxonomy also covers under Park Avenue / Madison Square. Different page, same cluster.

Class A and Renovated Loft Space

Step off the AI corridor and Flatiron is loft country. Renovated prewar and cast-iron buildings with high ceilings, big windows, and floor plates that suit a 5,000 to 40,000 SF tenant. This is where most Flatiron leases that are not AI megadeals get signed, and it is a deep pool. A lot of these landlords spent real money on lobbies and prebuilt spec suites over the last five years, so a 2026 Class A loft here often shows better than a glassy tower built in 2008. The character is the point, and tenants pay for it. The best of this stock spans Fifth Avenue, Broadway, and the blocks around the old Flatiron Building.

One thing to know: the Flatiron Building itself, at 175 Fifth Avenue, is no longer an option. After 120 years as offices it is being converted to 38 luxury condominiums, wrapping in fall 2026 (6sqft, 2026). The ground floor will keep retail, including a new restaurant from the team behind Bar Pisellino, but the office floors are gone. If you want the most famous triangular silhouette in America, you will have to buy a condo.

Class B and Value Loft Space

Here is where the value lives, and most tenants do not realize it is there. On the Sixth Avenue side, in the converted Ladies’ Mile department stores, and on the prewar side streets between Fifth and Sixth, Flatiron still has loft space that prices well below the Park Avenue South corridor. Savills’ Flatiron submarket averaged $64.66/SF in late 2025 against $77.50/SF for Park Avenue South, and that gap is the whole opportunity (Savills, Q4 2025). Same neighborhood, same trains, materially lower rent. This tier works for startups, small and midsize firms, medical and dental practices, nonprofits, and anyone who wants the Flatiron energy without the AI-corridor invoice.

Side-street buildings off Sixth in the West 18th to 22nd Street range carry strong 1,500 to 15,000 SF inventory, and a fair amount of it comes as spec suites you can move into fast. A chunk also trades as sublease, which can be the quickest, cheapest way in if the term fits. Two practical notes before you sign down here. First, the approved brokerages do not publish a standalone Class C average for Flatiron, so if anyone quotes you a single Class C number, they are guessing; the value-tier read here is Metro Manhattan internal research (May 2026). Second, almost every NYC landlord will want a security deposit, and for smaller or newer companies, a Good Guy Guarantee, so understand both before you negotiate. If you are coming out of a coworking space, our guide to scaling from coworking to your own office is the playbook.

Lease Concessions and Effective Rent

Here is where most tenants leave the most money on the table. They negotiate the asking rent, win a few dollars, and sign, and they never push hard on free rent or the build-out allowance, which is where the real value lives in a Flatiron loft deal. Who pays for the build-out is negotiable, and outside the white-hot AI corridor you have more room than you think. The ranges below are typical-market figures from our recent deals (Metro Manhattan internal research, May 2026), assuming a 5 or 10-year term. Shorter terms get smaller packages; 10 to 15-year terms pull richer ones.

One more thing: net effective rent typically lands well below the face rent your broker first quotes. The math takes ten minutes to learn and it is the difference between a fine deal and a great one. Our breakdown of 3-year, 5-year, or 10-year lease terms covers how term length moves the package, and our concessions explainer walks through the effective-rent math.

Which Business Fits the Flatiron District?

Flatiron tenants cluster tight by industry, and not by accident. AI and fintech want Park Avenue South and Madison Square. Media, creative, and showroom tenants want the lofts off Fifth and Sixth. Smaller firms want the prewar side streets. There is a logic to it: your clients, your talent, and the company down the block you want to poach from are already there. Match your industry to the right corridor and most of the search narrows itself. The table is the cheat sheet.

Running a lean team? Flatiron is not the cheapest corner of Manhattan, the deepest value is elsewhere, but the side streets off Sixth are competitive once you factor in the talent you can recruit by being in the AI neighborhood. Our guide to the top neighborhoods for small businesses lays out the trade-offs. And if you are chasing the AI cluster but priced out of Park Avenue South, the same energy is spilling into SoHo, Chelsea (where Clay leased before its move to 11 Madison), and even down to the Financial District, where Scale AI recently relocated to fit a workforce that doubled to 500 (The Real Deal, 2026).

Top Office Buildings and Amenities in the Flatiron District

If your last Flatiron tour was pre-2020, the picture in your head is wrong. The AI money pulled the amenity game up to Midtown trophy standards, and the best buildings here now compete on lounges and terraces, not just exposed brick. Three tiers to expect:

Trophy and Class A core (11 Madison, One Madison, Nomad Tower): Tenant-only amenity floors, conferencing, lounges, fitness, rooftop event space, and Madison Square Park views. Marquee on-site dining, with three-Michelin-star Eleven Madison Park at 11 Madison and La Tete d’Or by Daniel Boulud at One Madison. Smart-building systems. The top of Midtown South, full stop.

Renovated loft (28-40 West 23rd, 225 Park Avenue South, 122 Fifth Avenue, 200 Fifth Avenue): Restored lobbies, new mechanical systems, on-site fitness and conferencing in the bigger buildings, ground-floor retail, and the high ceilings and natural light that draw tenants to lofts in the first place.

Class B and value loft (71 West 23rd, 113-133 West 18th, side-street prewar stock): Prewar character, big windows, attended lobbies, tenant-controlled HVAC, and a growing number of fully built-out spec suites with furniture and cabling already in place so you can move in fast.

Featured Buildings

• 11 Madison Avenue: SL Green and PGIM’s 2.3M SF, 30-story full-block tower fronting Madison Square Park, the former Metropolitan Life North Building. Brought to 100% leased in Q1 2026 by Clay’s 163,000 SF AI lease at $90/SF (Commercial Observer, March 9, 2026). Tenants include UBS, Sony, William Morris Endeavor, Pinterest, and Tempus AI, and Eleven Madison Park sits on the ground floor.
• One Madison Avenue: SL Green’s redeveloped 1.4M SF Class A tower overlooking Madison Square Park, a restored nine-story podium under a new tower. Harvey AI expanded to roughly 185,000 SF here in Q1 2026, filling the building (SL Green, March 2026). Asking rents around $120/SF. Amenities include a rooftop event space, La Tete d’Or by Daniel Boulud, and Chelsea Piers Fitness.
• 28-40 West 23rd Street: Williams Equities’ two-building, 561,000 SF complex between Fifth and Sixth, the old Home Depot building. Fintech Ramp anchors it after expanding to 285,300 SF in Q1 2026, the largest Midtown South lease of the quarter (The Real Deal, April 2026). Renovated lobbies, new cooling towers, and a planned roof deck.
• 225 Park Avenue South (American Woolen Building): A 19-story prewar loft at Park Avenue South and 18th Street, two blocks above Union Square. A textbook Flatiron recovery story: it lost Meta and sat heavily vacant in 2024, and it has been filling back in as tech demand returned.
• The Flatiron Building (175 Fifth Avenue): The 1902 Beaux-Arts icon by Daniel Burnham, one of the world’s first skyscrapers. After 120 years as offices, the Brodsky Organization, GFP Real Estate, and Sorgente Group are converting it to 38 luxury condominiums, wrapping in fall 2026 (6sqft, 2026). No longer leasable office space, but the silhouette still defines the neighborhood.
• Nomad Tower (1250 Broadway): An amenity-rich Class A trophy at Broadway and 32nd on the NoMad edge, popular with finance, fintech, and professional-services tenants.
• 122 Fifth Avenue: Bromley Companies’ modern Flatiron development, where Microsoft leases roughly half the building. A rare new-construction option in a neighborhood built on conversions.

Ground-floor and flagship retail space along Fifth Avenue, Broadway, and the Ladies’ Mile stretch of Sixth is some of the highest-traffic retail in the neighborhood. If you are after a storefront rather than a floor upstairs, that is a different and very good search here.

Major Office Landlords in the Flatiron District

Who owns your building matters as much as which building you pick, because every major Flatiron landlord negotiates differently. SL Green, the city’s largest office landlord, owns both Madison Square anchors and just posted its best first quarter in 28 years, so it is dealing from strength and pushing hard (SL Green, March 2026). Williams Equities holds the Ramp building and runs a tight, well-capitalized shop. Smaller owners like Olmstead, Feil, and Bromley are aggressive on the Park Avenue South side and will move quickly for the right tenant. A good broker knows what you are walking into. For background, see our overview of the biggest commercial real estate landlords in NYC. Several of these owners also hold much larger portfolios in Downtown Manhattan, where the same dollar buys more space.

Transportation and Commuting to the Flatiron District

Flatiron sits in the dead center of Manhattan, which makes it a faster commute from almost everywhere than your team probably realizes. Union Square anchors the south end with eight subway lines, the 23rd Street stations cover the core, PATH runs to New Jersey, and Penn Station and Grand Central are both a short hop away. If anyone on your team is resisting the commute, send them our Commute Calculator with their home address. The numbers usually do the convincing.