Based on broadband/narrowband photometry andKeckDEIMOSspectroscopy, we report a redshift of z = 4.64⁺⁰˙⁰⁶₋₀․₀₈ for AzTEC/COSMOS 1, the brightest submillimeter galaxy (SMG) in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 μm), CSO/SHARC II (350μm), and CARMA and PdBI (3 mm). We do not detect CO(5 → 4) line emission in the covered redshift ranges, 4.56–4.76 (PdBI/CARMA) and 4.94–5.02 (CARMA). If the line is within this bandwidth, this sets 3σ upper limits on the gas mass to ≲8 × 10⁹M⊙ and ≲5 × 10¹°M⊙, respectively (assuming similar conditions as observed in z ∼ 2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV–IR spectral energy distribution of AzTEC 1 shows that it is an extremely young (_50 Myr), massive (M∗ ∼ 10¹¹ M⊙), but compact (≲2 kpc) galaxy, forming stars at a rate of ∼1300M⊙ yr⁻¹. Our results imply that AzTEC 1 is forming stars in a “gravitationally bound” regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.