How long will Google take to stop crawling an old URL once it has been 301 redirected

[Ant-808]

I need to do a clean-up old urls that have been redirected in sitemap and was wondering about this.

[RyanKent]

Google's crawler will always attempt to crawl any links it finds. If somewhere on the internet there is a link to an old URL and Google sees that link, it will never stop trying to explore that link. Each time it attempts to crawl the link, it will see the 301 and follow the redirect, but if you ever remove that redirect then the original URL will be seen.

[gmk1567]

I agree with Ryan. As long as the old URLs are out there in the web, Google will follow them.

At the same time, redirected URL list will be very lengthy if you are maintaining a big site and maintaining them will consume your resources.

Check link value of the old URLs as a first step. If they have no value then you will be fine to retire such old URLs.