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IIRC, AMD Polaris 460 or 450 (?)

From the order page:

Intel Iris Graphics 540 (13" sans Touch Bar)

Intel Iris Graphics 550 (13" with Touch Bar)

Radeon Pro 450 with 2GB memory (15")

Radeon Pro 455 with 2GB memory (15" top-end)

There's also option "Radeon Pro 460 with 4GB memory" [1]