Seattle-Tacoma International Airport is moving forward with a $2.5 billion modernization of its S Concourse, a major component of the airport’s $5.5 billion Upgrade SEA capital improvement program.

The Port of Seattle Commission authorized $1.1 billion in initial funding for the S Concourse Evolution project, which will renovate a facility originally built in 1973 and primarily used for international operations. Early work is expected to begin in late 2026, with major construction starting in 2027. The multiphase project is scheduled for substantial completion in 2034.

Rather than expanding the concourse outward, the airport plans to add approximately 150,000 square feet by repurposing space previously used for customs processing and constructing a new upper concourse level. The project will also improve dual-level boarding at select gates and expand dining, retail, lounge and passenger amenity areas.

The project will not add gates. Instead, improvements are designed to increase the capacity and efficiency of the existing facility while addressing aging structural, seismic and building systems. SEA officials said building vertically is particularly important because the airport has one of the smallest physical footprints among major U.S. airports relative to its passenger volume.

Construction will take place while the S Concourse remains operational. A temporary S Annex will be built east of the existing facility to support ground boarding during construction, with the airport aiming to have no more than three of the concourse’s 12 gates affected at one time.

Sustainability measures are also a significant part of the project. SEA is targeting LEED Silver certification and anticipates the improvements will reduce annual operational greenhouse gas emissions by 58% and annual energy use by 16% compared with Port standards. Planned features include high-performance glazing, enhanced building management and lighting systems, electric equipment in place of fossil fuel-powered systems, low-flow plumbing fixtures and electric vehicle charging for aircraft service equipment.

The S Concourse project follows several other major investments under Upgrade SEA. The airport completed its International Arrivals Facility in 2022 and C Concourse Expansion and SEA Gateway projects in 2026. Baggage system optimization and underground controls replacement projects are among the improvements still underway.

Funding for the S Concourse Evolution will come from the Airport Development Fund and future revenue bonds. The Port of Seattle said no taxpayer dollars will be used to fund the project.