  Multi-messenger searches for BNS and NSBH mergers are currently one of the
most exciting areas of astronomy. The search for joint electromagnetic and
neutrino counterparts to GWs has resumed with O4. To support this effort,
public semi-automated data products are sent in near real-time and include
localization and source properties to guide complementary observations. In
preparation for O4, we have conducted a study using a simulated population of
compact binaries and a MDC in the form of a real-time replay to optimize and
profile the software infrastructure and scientific deliverables. End-to-end
performance was tested, including data ingestion, running online search
pipelines, performing annotations, and issuing alerts to the astrophysics
community. We present an overview of the low-latency infrastructure and the
performance of the data products that are now being released during O4 based on
the MDC. We report the expected median latency for the preliminary alert of
full bandwidth searches (29.5s) and show consistency and accuracy of released
data products using the MDC. For the first time, we report the expected median
latency for triggers from early warning searches (-3.1s), which are new in O4
and target neutron star mergers during inspiral phase. This paper provides a
performance overview for LVK low-latency alert infrastructure and data products
using the MDC and serves as a useful reference for the interpretation of O4
detections.
