Code change:
The user agent includes stored cookies in the Cookie HTTP request header field. <del> When the user agent generates an HTTP request, the user agent MUST NOT attach more than one Cookie header field. </del> A user agent MAY omit the Cookie header field in its entirety.  For example, the user agent might wish to block sending cookies during "third-party" requests from setting cookies (see third-party- cookies). If the user agent does attach a Cookie header field to an HTTP <del> request, the user agent MUST compute the cookie-string following the algorithm defined in retrieval-algorithm, where the retrieval's URI is the request-uri, the retrieval's same-site status is computed for the HTTP request as defined in same-site-requests, and the retrieval's type is "HTTP". </del> <ins> request, the user agent MUST generate a single cookie-string and the user agent MUST compute the cookie-string following the algorithm defined in retrieval-algorithm, where the retrieval's URI is the request-uri, the retrieval's same-site status is computed for the HTTP request as defined in same-site-requests, and the retrieval's type is "HTTP". </ins> 5.7.2.

Related discussion:
text: This PR removes the requirement of checking the request's redirect chain during the computation of same-site-ness. This is being done because RFC6265bis is blocked by this work but we have yet to find a way to implement it in a web compatible way. In the interest of moving RFC6265bis forward the requirement is being removed.
The work to re-add the requirement back into RFC6265tris is being track by issue
Yeah, we did implement this - but we had to back it out (and re-spin stable, IIRC?) because it broke too many sites. :(
Correct, Chrome had to disable the change. Firefox had a similar experience.
We noticed a difference between Firefox & Chrome’s behavior for same-site cookies. Specifically, if a web page is requesting a resource whose final redirect target is same-site with the web page, . Firefox follows what was originally decided in URL and specified in recent i.e., Firefox looks at the whole redirect chain. For context: Firefox shipped SameSite=Lax by default this January and had to backpedal due to this (and some other webcompat issues). Firefox does not ship SameSite=Lax as the default setting for new cookies as of now. While we’re still working on our own metrics, we’ve noticed that Chrome is seeing about 1% of page loads potentially affected, which seems prohibitively high. At the same time, we would prefer not to weaken our implementation of explicit SameSite cookies, given that the redirect check was specifically added to prevent CSRF abuse scenarios. With these things in mind, we’ve been exploring the idea that we might treat cookies differently depending on whether the cookie was set to lax by default or is an explicit samesite cookie. NAME NAME it would be nice to hear some thoughts about this idea and also NAME how other browsers may have implemented . CC: NAME NAME NAME NAME NAME NAME
Yeah, I agree this is unfortunate. We did , but it broke a few sites and was backed out (or rather, put behind an off-by-default feature flag). NAME has been collecting better metrics so we can hopefully make progress on this. Can you give some more detail what you're thinking here? (also cc NAME


With these things in mind, we’ve been exploring the idea that we might treat cookies differently depending on whether the cookie was set to lax by default or is an explicit samesite cookie.