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Several efforts are underway to better understand the current degradation phenomenon in ITER Nb3Sn cable-in-conduit (CIC) conductors, using an electric circuit model of the strand interior. To support these efforts, this paper explores crack formation and filament coupling through microstructural observation of ITER-type Nb3Sn strands under bending strain. Cracks began to appear at bending strains well below 1%, even in bronze-route Nb3Sn strands, and typically appeared around 0.3%. In internal-tin Nb3Sn strands, the strain causing crack formation decreased further, to about 0.25%. Magnetization measurements detected filament coupling, even in bronze-route Nb3Sn strands. However, the effective filament diameter was so small that its influence on Ic-bending strain characteristics should be limited.