Higgs Decay to Order αₛ⁴

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We present in analytic form the three-loop O(αₛ²) correction to the H -> gg partial width of the standard-model Higgs boson with intermediate mass Mₕ << 2 Mₜ. Its knowledge is required because the O(αₛ) correction is so sizeable that the theoretical prediction to this order is unlikely to be reliable. For Mₕ=100 GeV, the resulting QCD correction factor reads 1+(215/12)αₛ⁽⁵⁾(Mₕ)/π+150.419 (αₛ⁽⁵⁾(Mₕ)/π)² ≈ 1+0.66+0.21. The new three-loop correction increases the Higgs-boson hadronic width by an amount of order 1%.