Koyn

Koyn in London opened in September 2022 and immediately presented a clear identity: Modern Japanese cuisine with a rising Thai fire element, set in a two-storey Mayfair address at 38 Grosvenor Street. From the moment you approached the former US embassy façade, the idea was obvious — an upstairs Midori space that served precise sushi and lighter plates and a subterranean Magma room built around a charcoal robata for grilled intensity. Koyn placed modern Japanese techniques at its core while inviting bold spices and tropical ingredients to punctuate dishes, giving London diners a distinct, appetite-driven experience. The restaurant name appears on reservations for business lunches, dates and special evenings in central London.

To reserve, guests used the listed phone or online channels when available, reflecting a practical approach to bookings in Mayfair. Koyn welcomed guests with table service and an intimate sushi counter for close viewing of technique. The restaurant always emphasized ingredient clarity, texture contrast and focused seasoning, making each course feel purposeful. The culinary vision came to life under executive chef Rhys Cattermoul, who joined Koyn with a pedigree that included time at Nobu.

His approach combined precise sushi craft, robata grilling and an openness to Thai flavors introduced in 2024 via a downstairs Koyn Thai identity. Cattermoul prioritized authentic ingredients and clear technique; examples include steamed clams ‘nabe’ finished with cordyceps mushroom and yuzu sake soy, or a wagyu tenderloin showing restrained seasoning to highlight fat and beef quality. There were no major industry awards listed in source material, but guest feedback and London reviews praised the team for excellent service and standout Thai flavours. Koyn’s philosophy aimed to tell a culinary story in two acts: delicate, marble-bar sushi upstairs and fire-forward grilled dishes below.

This duality informed menu design, staff training and the pacing of a meal, giving diners choice between refined tasting elements and louder, grill-driven plates. Signature dishes demonstrated that intent. Salmon tataki arrived with a mustard-forward sauce to cut through oil and provide a bright counterpoint. The wagyu Japanese beef tenderloin was served simply to showcase marbling and texture, often paired with grilled seasonal vegetables pulled from the robata.

Steamed clams ‘nabe’ married sea saltiness with umami-rich cordyceps and the citrus lift of yuzu, offering a comforting bowl that still felt refined. The sushi offering relied on a marble sushi counter where fish was sliced to order and served with measured soy and wasabi to preserve texture. Desserts received notable praise, an uncommon compliment for a sushi-led spot, rounding the menus with approachable, well-balanced sweets. Seasonal rotations were suggested by the kitchen’s emphasis on fresh produce and grill-driven changes, but standard heroes like wagyu and tataki remained consistent.

The interior split into two carefully designed atmospheres. Midori featured light green leather banquettes, iridescent oyster-shell wall treatments and a marble sushi bar that invited observation. Magma’s lower level used black oak ceilings, burnt orange seating and an exposed charcoal robata to create a room where flames and smoke shaped flavor. Service was friendly and professional, with staff guiding pairings from a very good wine cellar and offering vegetarian and vegan options.

The layout supported intimate counter seating, small tables for business lunches and a livelier bar scene for evening dates. For practical planning, Koyn operated primarily Thursday to Saturday with lunch and evening services as of April 2025. Reservations were recommended, especially for the sushi counter or weekend evenings; call +44 20 3535 2000 for the most direct booking route. Koyn closed on 27 September 2025 after a three-year run; its kitchen and concept left a clear impression on Mayfair’s dining scene and the Koyn name continues as a reference point for Modern Japanese-Thai fusion in London.

For diners seeking the combination of precise sushi technique and a robust robata grill experience, Koyn remains a memorable chapter in Mayfair gastronomy and a model for high-end, flavor-forward Japanese dining in central London.