AT&T has powered down its final No. 4 Electronic Switching System (4ESS) in Anchorage, Alaska, marking a major milestone in the ongoing evolution of our network. The retirement closes the chapter on a technology that helped power long-distance calling for more than half a century while demonstrating how our network continues to move toward modern, software-driven platforms built for today's communications needs.
An Ever-Evolving Network
Rows of 4ESS equipment are shown in an AT&T switching office in Chicago in the late 1970s.
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Introduced in the 1970s, 4ESS switching technology carried long-distance calls that helped connect people and businesses across the country. By today’s standards, these switches were enormous — occupying as much as 5,000 square feet, larger than a professional basketball court.
For decades, the 4ESS switch played an important role in routing long-distance voice traffic across the U.S. But the way people connect has changed dramatically. Today, customers rely on AT&T for mobile, fiber, cloud-based applications, streaming, digital communications and more.
To support those evolving needs, AT&T is modernizing the network by moving functions previously handled by the 4ESS switch to a next-generation platform designed to enhance efficiency, flexibility, and long-term service reliability. The difference in physical footprint is significant: what once required more than 100 equipment bays and up to 5,000 square feet can now be supported in about 4 bays, occupying roughly 28 square feet — about the size of a pool table. This transition helps AT&T continue supporting long-distance voice services while reducing reliance on aging equipment and preparing the network for the future. This work is part of AT&T’s broader transformation toward a fully IP-enabled fiber network by 2029.
From up to 5,000 square feet to about the size of a pool table.
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Unique Challenges in Alaska
While the broader transition away from legacy voice infrastructure has been underway for years, retiring the final 4ESS presented unique challenges. The last remaining switch was located in Anchorage, Alaska, a fitting final frontier. Given Alaska’s vast geography and the importance of maintaining dependable connectivity across the state, the effort required careful planning and close coordination across engineering teams and network partners to migrate traffic and complete the transition seamlessly for customers.
This milestone reflects our continued work to modernize and strengthen the network. In Alaska, we invested more than $200 million in our network from 2021-2025 to build more infrastructure and power more opportunities. Communities throughout Alaska are seeing the impacts of this investment, including nearly $90 million in Anchorage.
Power switch for a 4ESS system is shown the night it was powered down in Anchorage, Alaska.
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Built on a Strong Foundation
When 4ESS switching technology was introduced, long-distance calling was one of the primary ways people stayed connected. Today, our customers rely on us for far more, from mobile connectivity and streaming to cloud-based applications and digital communications. As those needs have evolved, so has the network supporting them. The 4ESS helped build the foundation for long-distance communication as we knew it. Its retirement marks the end of an important chapter in history and reflects how our network continues to evolve.
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