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Y dwarfs, the coolest known spectral class of brown dwarfs, overlap in massand temperature with giant exoplanets, providing unique laboratories forstudying low-temperature atmospheres. However, only a fraction of Y dwarfcandidates have been spectroscopically confirmed. We present Keck/NIRESnear-infrared spectroscopy of the nearby ($d \approx 6-8$ pc) brown dwarf CWISEJ105512.11+544328.3. Although its near-infrared spectrum aligns best with theY0 standard in the $J$-band, no standard matches well across the full $YJHK$wavelength range. The CWISE J105512.11+544328.3 NH$_3$-$H$ = 0.427 $\pm$ 0.0012and CH$_4$-$J$ = 0.0385 $\pm$ 0.0007 absorption indices and absolute Spitzer[4.5] magnitude of 15.18 $\pm$ 0.22 are also indicative of an early Y dwarfrather than a late T dwarf. CWISE J105512.11+544328.3 additionally exhibits thebluest Spitzer [3.6]$-$[4.5] color among all spectroscopically confirmed Ydwarfs. Despite this anomalously blue Spitzer color given its low luminosity,CWISE J105512.11+544328.3 does not show other clear kinematic or spectralindications of low metallicity. Atmospheric model comparisons yield a log(g)$\le$ 4.5 and $T_{\rm eff} \approx 500 \pm 150$ K for this source. We classifyCWISE J105512.11+544328.3 as a Y0 (pec) dwarf, adding to the remarkablediversity of the Y-type population. JWST spectroscopy would be crucial tounderstanding the origin of this Y dwarf's unusual preference for low-gravitymodels and blue 3-5 $\mu$m color.

CWISE J105512.11+544328.3: A Nearby Y Dwarf Spectroscopically Confirmed with Keck/NIRES