[15 September 2021 update; next update by 15 November 2021]

The LIGO-Virgo-KAGRA Collaboration is continuing to evaluate and respond to the ongoing impacts of COVID-19 and adverse weather on preparations for the O4 observing run. As a result, we reiterate that O4 will not start before August 2022 and note that it may be further delayed. We will provide a more concrete plan in our next update, by 15 November 2021.

The readiness of both the LIGO-Hanford and the LIGO-Livingston detectors remains uncertain as delays due to COVID-19 and Hurricane Ida hitting Louisiana have affected the construction schedule for the Frequency Dependent Squeezing system. Hurricane Ida has also impacted the LIGO Livingston Observatory staff and their families. The full impacts are still being evaluated and mitigations are being identified.

Virgo has completed the integration of the upgrades for O4 and is now in a commissioning phase. The uncertainty in readiness of the Virgo detector is mainly driven by the progress of the instrument commissioning.

KAGRA is working to join O4 with Virgo and LIGO. A later start than August 2022 is preferable due to COVID-19 and staff limitations.

If you have any questions, please contact the Spokespersons:

● Patrick Brady (Spokesperson, LIGO Scientific Collaboration); lsc-spokesperson_AT_ligo/org
● Giovanni Losurdo (Spokesperson, Virgo Collaboration); virgo-spokesperson_AT_ego-gw/it
● Jun’ichi Yokoyama (Board Chair, KAGRA Scientific Congress); kscboard-chair_AT_icrr/u-tokyo/ac/jp
  (Please replace “_AT_” into “@” and replace “/” into “.” after it.)