Google and Bing both announced today that they have raised the file size limits on their sitemaps from 10mb up to 50mb. The 50,000 URL limit hasn’t changed however. Here is an excerpt directly from the Sitemap.org protocol:
You can provide multiple Sitemap files, but each Sitemap file that you provide must have no more than 50,000 URLs and must be no larger than 50MB (52,428,800 bytes). If you would like, you may compress your Sitemap files using gzip to reduce your bandwidth requirement; however the sitemap file once uncompressed must be no larger than 50MB. If you want to list more than 50,000 URLs, you must create multiple Sitemap files.
The change was announced earlier this morning by Google on Twitter:
We've updated the Sitemaps protocol with Bing! Sitemaps & indexes can be considerably larger now. More at https://t.co/uygpuywUEh
— Google Webmasters (@googlewmc) November 30, 2016