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Schneider et al. (2020) presented the discovery of WISEA J041451.67-585456.7and WISEA J181006.18-101000.5, which appear to be the first examples of extremeT-type subdwarfs (esdTs; metallicity <= -1 dex, T_eff <= 1400 K). Here wepresent new discoveries and follow-up of three T-type subdwarf candidates, withan eye toward expanding the sample of such objects with very low metallicityand extraordinarily high kinematics, properties that suggest membership in theGalactic halo. Keck/NIRES near-infrared spectroscopy of WISEAJ155349.96+693355.2, a fast-moving object discovered by the Backyard Worlds:Planet 9 citizen science project, confirms that it is a mid-T subdwarf. WithH_W2 = 22.3 mag, WISEA J155349.96+693355.2 has the largest W2 reduced propermotion among all spectroscopically confirmed L and T subdwarfs, suggesting thatit may be kinematically extreme. Nevertheless, our modeling of the WISEAJ155349.96+693355.2 near-infrared spectrum indicates that its metallicity isonly mildly subsolar. In analyzing the J155349.96+693355.2 spectrum, we presenta new grid of low-temperature, low-metallicity model atmosphere spectra. Wealso present the discoveries of two new esdT candidates, CWISEJ073844.52-664334.6 and CWISE J221706.28-145437.6, based on their large motionsand colors similar to those of the two known esdT objects. Finding more esdTexamples is a critical step toward mapping out the spectral sequence andobservational properties of this newly identified population.

New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project