Hotel Costes was the French capitals coolest address, and now the property has an equally-chic sibling, Castiglione.

Styled by Ewa Kluczenko.

Model: Nelly Herin at Girl MGMT.

Fashion shoot at the Hotel Costes, in Paris, France

Dolce & Gabbana strapless dress, $2,370; dolcegabbana.com. Nina Ricci pumps in semi-patent leather, $700; nina ricci.com.Cerruti & Draime

Hair by Olivier Noraz.

Makeup by Ania Grzeszczuk at Calliste.

Manicure by Julie Villanova at Artlist.

Fashion shoot at the Hotel Costes, in Paris, France

Left: Y/Project Contraband coat, $1,755; yproject.fr. Brunello Cucinelli blouse, $1,875, and leather trousers, $5,095; 136 Greene St., N.Y.C.; 212-334-1010. Salvatore Ferragamo F Heel slingbacks, $850; ferragamo.com. Vanessa Schindler chain earrings, $213; vanessa-schindler.com. Right: Chanel cashmere cardigan, $4,250. Dolce & Gabbana strapless dress, $2,370; dolcegabbana.com.Cerruti & Draime

Especially given the competition in Paris, wherepalatial hotelsproliferate like rabbits.

And especially amongfashion people, Costes’s core clientele.

Their attention spans are not long and their tastes are, by definition, fickle.

Fashion shoot at the Hotel Costes, in Paris, France

Left: Louis Vuitton knit tank, $950; louis vuitton.com. Chanel cotton-drill jacket, $6,550, and shorts, $1,650; 800-550-0005. Right: Lemaire trench coat, $1,088, Ramirez shirt, $839, and asymmetrical Bermuda shorts, $632; us.lemaire.fr. Salvatore Ferragamo F Heel slingbacks, $850; ferragamo.com. Vanessa Schindler chain earrings, $213; vanessa-schindler.com.Cerruti & Draime

But many of themthe entire press and design team at Valentino, for examplewon’t go anywhere else.

(Those are his portraits of the Costes staff in the hallway on the second floor.)

Downton describes his stays for the haute couture shows in January and July as “habit-forming.”

Fashion shoot at the Hotel Costes, in Paris, France

The portico at Castiglione.Cerruti & Draime

“you could smoke on the restaurant patio, and you’ll always see someone there.

It’s a parade.”

“you’re free to smoke on the restaurant patio, and you’ll always see someone there.

Fashion shoot at the Hotel Costes, in Paris, France

Left: The hotel’s interior staircase. Right: Vejas side-split dress, $795; shop.vejas-k.com. Burberry leather hoop earrings, $490; us.burberry.com.Cerruti & Draime

You know when the Chanel show is happening because people pile in wearing Chanel.”

But after all this magnificent intransigence, there is now a place for minimalism and daylight at the Costes.

Yes, the hotel is changing.

Fashion shoot at the Hotel Costes, in Paris, France

Left: Fifi Chachnil cardigan, $435; fifichachnil.paris. Lou de Bètoly bra, price upon request; loudebetoly.com. Chanel cotton-jacquard pants, $1,950, and goatskin-suede shoes, $1,200; 800-550-0005. Right: Velvet complements the hotel’s spare interiors.Cerruti & Draime

In contrast to the Costes, even the smallest rooms are nearly 500 square feet.

More deluxe suites have rowing machines in the bathrooms.

Castiglione has a general managersomething Costes never had.

If the new property doesn’t convert St.-Honore partisans, well, it doesn’t have to.

How radically flexible.Vive la difference.

Doubles at Castiglionefrom $1,450.