Soon limits for both keywords and negative keywords in Yandex.Direct will be increased. The current limit for an ad group is 4096 characters. This limit will no longer be applied to the whole group, but instead to each keyword and its negative keywords. In addition, you will be able to add up to 200 keywords to each group.

Please check that your campaigns comply with the new limits. In API 4 and 4 Live, the new limits are supported by the CreateOrUpdateBanners and CreateOrUpdateBanners (Live) methods, while the add and update methods of the Keywords service are supported in version 5.