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Google has just announced fresh documentation covering three common scenarios involved with moving a website, which includes a responsive web design and dynamic serving recommendation for each of the following:

1) Moving from separate URLs to the same URLs
2) Moving from the same URLs to separate URLs
3) Switching from responsive web design to dynamic serving or visa versa

What I'm a little confused by is the use of 302 redirects in the documentation, that seems like the wrong approach to me and I'm hoping it is just a typo.

For instance if you were going from separate URLs for mobile and moving to a single set of URLs for desktop/tablet/mobile and using responsive web design or dynamic serving -- you'd want to issue a HTTP 301 permanent redirect from the now defunct mobile specific URLs into their corresponding desktop URLs.

I'm hoping that +John Mueller, +Pierre Far or +Zineb Ait Bahajji can clarify if this a deliberate change or not? If it is deliberate, why has the recommendation for this changed from using a 301 redirect to using a 302 redirect?
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Alistair Lattimore's profile photoKen Hirooka's profile photoPascal Landau's profile photoCharu Rastogi's profile photo
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Asked Google at SMX Advanced... +Maile Ohye said it is not a typo, it is on purpose and +Matt Cutts said it was so they can change it, if they want in the future, so it is not permanent. 
 
They used to say "it doesn't matter" if 301 or 302, see archived version on https://web.archive.org/web/20140102122923/https://developers.google.com/webmasters/smartphone-sites/redirects

Using HTTP redirection
HTTP redirection is a commonly used to redirect clients to device-specific URLs. Usually, the redirection is done based on the user-agent in the HTTP request headers. It is important to keep the redirection consistent with the alternate URL specified in the page's link rel="alternate" tag or in the Sitemap.
For this purpose, it does not matter if the server redirects with an HTTP 301 or a 302 status code.

However, that has changed since february an currently says on
 https://developers.google.com/webmasters/smartphone-sites/redirects?hl=en :

Using HTTP redirection
HTTP redirection is a commonly used to redirect clients to device-specific URLs. Usually, the redirection is done based on the user-agent in the HTTP request headers. It is important to keep the redirection consistent with the alternate URL specified in the page's link rel="alternate" tag or in the Sitemap.
For this purpose, it does not matter if the server redirects with an HTTP 301 or a 302 status code, but use of 302 is recommended whenever possible.


Btw. the downside of the 302-solution is that it's not cached so that your smartphone will have to make an additional request when you're accessing the desktop version a second time.
 
+Pascal Landau thanks for adding that detail for everyone reading.

I'm aware that the documentation has said 301/302 in the past but that is inconsistent with the recommendations for moving a website for example - which uses a 301.

What I don't understand is why they'd say it is okay to use either in this context - if you're decommissioning separate URLs and moving toward responsive/dynamic serving - why would you want to keep the old URLs around by issuing a 302 redirect?

Granted it means you could change your mind in the future and revert to using those URLs again but I wouldn't think that'd be a common scenario where a business - surely?

In the past Google have said that if you use a 302 redirect (for whatever purpose) and it is stable and in place long enough, that they will treat it like a 301. If that's the case, why not just use a 301 in the first place?

Just seems odd to me, some consistency on these things would help everyone (internet marketing folk and an average person alike) understand these things a lot easier.
 
https://productforums.google.com/forum/#!mydiscussions/webmasters/urvOsklTB4Y

On that forum thread, I guessed that  302 recommendation is to prevent distribution of contents from cache, which can cause distribution of improper contents to user agents.
In Japanese/Chinese version of the documentation, Google recommends using server-side 302 HTTP redirects "and Cache-Control: private header". 
It is weird that English version doesn't have such suggestion, but I guess "Cache-Control: private header" may be for the same purpose.
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