KT Puts an 800-Gig AI Line on 840,000 Kilometres of Its Own Fibre

South Korean operator KT has launched an “AI-only” dedicated line service that sells 400 Gbit/s and 800 Gbit/s of bandwidth between data centres, and it is doing the job on fibre it already owns, with no new routes built for it. The previous ceiling on these circuits was 100 Gbit/s, which the operator says covers replication, video backhaul and ordinary cloud traffic and nothing more.

The gap the service targets is the one that shows up when a training job has to be synchronized across several AI data centres. Upgrading the port does not make the first byte of a transfer arrive sooner; it changes how many bytes can be in flight at once. KT describes the difference as a one-lane road widened into eight lanes, which is roughly what the eight-times capacity increase buys.

The operator says it built the lines on all-photonic network technology, which keeps traffic in the optical domain instead of converting it back to electrical signals along the path. KT did not disclose pricing for either tier. It also said it plans to extend the service to data centre operators and enterprises building their own AI infrastructure, and not only to other carriers, and it is pitching the service at large-volume transfers between distributed AI sites where a single-site cluster would not need it.

The fibre claim behind the pitch is the part competitors cannot copy quickly. KT says it holds 840,000 kilometres of nationwide optical cable and enough route diversity to design shortest and dual paths between multiple sites, a statement it made to the Seoul Economic Daily. Local operators told Korean media that networks capable of connecting AI data centres reliably are now treated as infrastructure of national importance as those centres spread across the country.

The market around the service is already priced in. Dell’Oro Group put worldwide optical transport equipment revenue up 15 percent year over year in the second quarter of 2026, with data centre interconnect revenue from IPoDWDM ZR/ZR+ and WDM systems growing 45 percent in the same period. The same research house estimates that more than 40 percent of optical transport equipment revenue in the quarter came from North America, where most of the largest AI data centres sit, and it notes that optical suppliers are reporting growing order backlogs as lead times stretch.

KT’s launch lands in that supply picture. An operator that owns the fibre can provision the path and skip the availability queue that constrains competitors buying capacity on leased routes.

Supplier’s note: Dedicated 400G and 800G circuits on leased fibre are what most of our carrier and integrator customers ask for, and the constraint is rarely the router end. We hold QSFP28 and 400G ZR+ optical modules in stock in Shenzhen, with ready-to-ship units leaving inside two working days and bulk orders of 50 units or more taking one to two weeks where a specific reach class is on allocation. Where an OEM ZR+ module sits on allocation we quote cross-reference equivalents matched to the same reach and reach class, and record the transmit power and bit-error-rate figures for every module on the test bench before dispatch. Field engineers report that the recurring failures are dirty fibre connectors on the patch panel and mismatched attenuators, so every data centre interconnect order ships with cleaning cassettes and a spare set of patch cords. Data centre operators, wholesale carriers and network integration firms building DCI between two or three sites are the usual buyers, and orders arrive as mixed pallets for single-link projects, priced per port once freight and duty are quoted.