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We have performed a search over 3440 deg$^2$ of Epoch 1 (2017-2019) of theVery Large Array Sky Survey to identify unobscured quasars in the optical ($0.2< z < 3.2$) and obscured active galactic nuclei (AGN) in the infrared that havebrightened dramatically in the radio over the past one to two decades. Thesesources would have been previously classified as "radio-quiet" quasars based onupper limits from the Faint Images of the Radio Sky at Twenty Centimeterssurvey (1993-2011), but they are now consistent with "radio-loud" quasars($L_{\rm 3\,GHz} = 10^{40 - 42} \,\, {\rm erg} \,{\rm s}^{-1}$). Aquasi-simultaneous, multiband ($\sim1-18$ GHz) follow-up study of 14 sourceswith the VLA has revealed compact sources ($<0.1^{\prime \prime}$ or $<1$ kpc)with peaked radio spectral shapes. The high-amplitude variability over decadaltimescales at 1.5 GHz (100% to $>$2500%), but roughly steady fluxes over a fewmonths at 3 GHz, are inconsistent with extrinsic variability due to propagationeffects, thus favoring an intrinsic origin. We conclude that our sources arepowerful quasars hosting compact/young jets. This challenges the generallyaccepted idea that "radio-loudness" is a property of the quasar/AGN populationthat remains fixed on human timescales. Our study suggests that frequentepisodes of short-lived AGN jets that do not necessarily grow to large scalesmay be common at high redshift. We speculate that intermittent but powerfuljets on subgalactic scales could interact with the interstellar medium,possibly driving feedback capable of influencing galaxy evolution.

Quasars That Have Transitioned from Radio-quiet to Radio-loud on Decadal Timescales Revealed by VLASS and FIRST