  We present the Young Supernova Experiment Data Release 1 (YSE DR1), comprised
of processed multi-color Pan-STARRS1 (PS1) griz and Zwicky Transient Facility
(ZTF) gr photometry of 1975 transients with host-galaxy associations,
redshifts, spectroscopic/photometric classifications, and additional data
products from 2019 November 24 to 2021 December 20. YSE DR1 spans discoveries
and observations from young and fast-rising supernovae (SNe) to transients that
persist for over a year, with a redshift distribution reaching z~0.5. We
present relative SN rates from YSE's magnitude- and volume-limited surveys,
which are consistent with previously published values within estimated
uncertainties for untargeted surveys. We combine YSE and ZTF data, and create
multi-survey SN simulations to train the ParSNIP and SuperRAENN photometric
classification algorithms; when validating our ParSNIP classifier on 472
spectroscopically classified YSE DR1 SNe, we achieve 82% accuracy across three
SN classes (SNe Ia, II, Ib/Ic) and 90% accuracy across two SN classes (SNe Ia,
core-collapse SNe). Our classifier performs particularly well on SNe Ia, with
high (>90%) individual completeness and purity, which will help build an anchor
photometric SNe Ia sample for cosmology. We then use our photometric classifier
to characterize our photometric sample of 1483 SNe, labeling 1048 (~71%) SNe
Ia, 339 (~23%) SNe II, and 96 (~6%) SNe Ib/Ic. YSE DR1 provides a training
ground for building discovery, anomaly detection, and classification
algorithms, performing cosmological analyses, understanding the nature of red
and rare transients, exploring tidal disruption events and nuclear variability,
and preparing for the forthcoming Vera C. Rubin Observatory Legacy Survey of
Space and Time.
