The ARRL has set a new standard for what counts as low power for ARRL-sponsored HF contests. The new limit is 100 W, which is down from the 150 W limit that has been permitted in some events, including the ARRL November Sweepstakes.
With the exception of the ARRL Field Day, this change goes into effect on 1 January 2022, for all ARRL-sponsored HF contests, as well as the IARU HF World Championship in July 2022.
This change has been implemented to standardize low-power categories within the contesting community. However, on a more practical level, the typical modern HF transceiver has a maximum power output of 100 watts.