Code change:
however, prudent to ensure that this designation is not the extent of a site's defense against CSRF, as same-site navigations and submissions can certainly be executed in conjunction with other <del> attack vectors such as cross-site scripting. </del> <ins> attack vectors such as cross-site scripting or abuse of page redirections. Understanding how and when a request is considered same-site is also important in order to properly design a site for SameSite cookies. For example, if a top-level request is made to a sensitive page that request will be considered cross-site and SameSite cookies won't be sent; that page's sub-resources requests, however, are same-site and would receive SameSite cookies.  Sites can avoid inadvertently allowing access to these sub-resources by returning an error for the initial page request if it doesn't include the appropriate cookies. </ins> Developers are strongly encouraged to deploy the usual server-side defenses (CSRF tokens, ensuring that "safe" HTTP methods are

Related discussion:
text: (I believe this is intended by latest draft, but as NAME pointed this might need some changes to the Storage Model section) NAME Could you help clarify more about "2 min Lax+POST mitigation"? I see it mentioned above but it would be great to discuss how the mitigation should behave exactly.
URL is the spec language around the behavior. As a quick refresher: the goal is to allow unsafe http methods (commonly POST) to attach cookies that do not specify a attribute but are being treat as "lax by default". This behavior is intended for newly created cookies and so has a lifetime limit of up to 2 minutes. Let me know if you have any more specific questions.
We (NAME NAME NAME and I) discussed this at TPAC and came to the following suggestion: We think that browsers have to apply a compatibility measure here, and it could be including cookies on cross-site redirects if they’re younger than, for example, 2 minutes. We’ll collect metrics to get a better understanding of what that number should be. We will update "Lax-Allowing-Unsafe" in the spec to document that behavior, which would make Chromium compliant to that and Firefox could (AFAIU) ship a compliant version as well. We’ll continue to recommend "Lax-Allowing-Unsafe" as the default behavior in the spec. We’ll note that this is a compatibility mechanism that browsers may support or not support at their own discretion. It's not a behavior sites should opt into.
I believe the "same-site redirect chain consideration" change should be removed from RFC6265bis, with the intention of adding it back to RFC6265Tris. RFC6265bis contains a number of improvements over RFC6265 that are being stalled due to UAs being unable to implement "same-site redirect chain consideration" in a web compatible way. My efforts examining metrics collected by Chrome haven't yet offered much insight into how this issue could be solved and I have no idea how much longer it could take. Because no UAs (to my knowledge) have shipped "same-site redirect chain consideration" I don't believe reverting the language will have any practical effect and shouldn't weaken any active protections. But publishing RFC6265bis as a new spec will have a number of benefits, including security/privacy benefits for the web's users.
This seems like a reasonable, pragmatic step to me.