[en] We present 0.95–1.80 μm spectroscopy of the ∼12–27 M_Jup companion orbiting the faint (R ∼ 13.6), young (∼120 Myr) M-dwarf 2MASS J01225093–2439505 (“2M0122–2439 B”) at 1.″ 5 separation (50 AU). Our coronagraphic long-slit spectroscopy was obtained with the new high contrast imaging platform Very Large Telescope Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) during Science Verification. The unique long-slit capability of SPHERE enables spectral resolution an order of magnitude higher than other extreme AO exoplanet imaging instruments. With a low mass, cool temperature, and very red colors, 2M0122–2439 B occupies a particularly important region of the substellar color–magnitude diagram by bridging the warm directly imaged hot planets with late-M/early-L spectral types (e.g., β Pic b and ROXs 42Bb) and the cooler, dusty objects near the L/T transition (HR 8799bcde and 2MASS 1207b). We fit BT-Settl atmospheric models to our R ≈ 350 spectrum and find $T_{\mathrm{e}\mathrm{f}\mathrm{f}}$ = 1600 ± 100 K and $\mathrm{l}\mathrm{o}\mathrm{g}(g)$ = 4.5 ± 0.5 dex. Visual analysis of our 2M0122–2439 B spectrum suggests a spectral type L3–L4, and we resolve shallow J-band alkali lines, confirming its low gravity and youth. Specifically, we use the Allers and Liu spectral indices to quantitatively measure the strength of the FeH, VO, KI, spectral features, as well as the overall H-band shape. Using these indices, along with the visual spectral type analysis, we classify 2M0122–2439 B as an intermediate gravity object with spectral type L3.7 ± 1.0.