There would be an increase in the site map file size limit from 10 MB to 50 MB.
Until the update on 30 November, sitemap files have been limited up to 50,000 URLs with an uncompressed file size of 10MB or below. But now, The files should contain a maximum of 50,000 URLs and the site map file has increased tremendously from 10 MB to 50 MB.
This announcement by Bing had been published in a blog update in which Bing’s Principal Program Manager, Fabrice Canel mentioned that it is very rare that a size exceeding 10MB shows up but it does happen on occasion and that is why the site map file limit has been increased.
Most of the sitemaps are under 10MB file limit, But these days our systems randomly encounter sitemaps exceeding 10MB. Very often this can happen when sitemap files list very long URLs or if they have alternate language URLs, Image URLs which inflates/increases the size.