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Evidence from different probes of the stellar initial mass function (IMF) ofmassive early-type galaxies (ETGs) has repeatedly converged on IMFs morebottom-heavy than in the Milky Way (MW). This consensus has come under scrutinydue to often contradictory results from different methods on the level ofindividual galaxies. In particular, a number of strong lensing probes areostensibly incompatible with a non-MW IMF. Radial gradients of the IMF --related to gradients of the stellar mass-to-light ratio $\Upsilon$ -- canpotentially resolve this issue. We construct Schwarzschild models allowing for$\Upsilon$-gradients in seven massive ETGs with MUSE and SINFONI observations.We find dynamical evidence that $\Upsilon$ increases towards the center for allETGs. The gradients are confined to sub-kpc scales. Our results suggest thatconstant-$\Upsilon$ models may overestimate the stellar mass of galaxies by upto a factor 1.5. For all except one galaxy, we find a radius where the totaldynamical mass has a minimum. This minimum places the strongest constraints onthe IMF outside the center and appears at roughly 1 kpc. We consider the IMF atthis radius characteristic for the main body of each ETG. In terms of the IMFmass-normalization $\alpha$ relative to a Kroupa IMF, we find on average aMW-like IMF $<\alpha_{main}> = 1.03 \pm 0.19$. In the centers, we findconcentrated regions with increased mass normalizations that are less extremethan previous studies suggested, but still point to a Salpeter-like IMF,$<\alpha_{cen}> = 1.54 \pm 0.15$

Dynamical stellar mass-to-light ratio gradients: Evidence for very centrally concentrated IMF variations in ETGs?