Objective: Evaluate the agreement between the GT3X+ and GT9X link with respect to the vertical axis under laboratory and free-living conditions using the normal filter and low frequency extension (LFE) filter, respectively and to evaluate the agreement between the minutes spent in different activity intensities between the devices under free-living conditions using both the normal and LFE filter, respectively. Methods: Eight participants (mean age = 28.3 ± 3.8) were enrolled. Participants completed four walking trials of two different speeds [2 and 3 miles per hour (mph), 3-minute stages] while wearing two GT3X+ and two GT9X link accelerometers on an elastic belt on the right sides of the hip. They continued wearing them for another 6–10 hours in the free-living setting. Results: There were no significant differences between the mean counts per minute between the devices for the walking trials and free-living assessment when both filters were applied. There were also no significant differences in the different physical activity intensity categories. There was strong evidence of agreement between the GT3X+ and GT9X link. Conclusion: Data collected with the GT3X+ and GT9X link should be comparable across past and future studies.