Since the nightly update to SVT-AV1 4.0.1 on 29-Jan-2026, using Tune=SSIM (tune=2) is changing to MS_SSIM (tune=4) at the encoder. In the docs SSIM and MS_SSIM are different and change different items. MS_SSIM also leads to a much greater bitrate. I believe this is a bug, but would like to ask before reporting. Note in the log that in line 330 Tune is still ssim in the passed structure, but in line 349, Tune is MS-SSIM

activity_log_main.4892 - 5-crf28-ssim-216.txt.zip