I care. I care that I even if I log off, even if I use a vpn, even if I go into incognito mode, they still can associate my requests with the account I initially logged in.

The problem is any website can do that. Incognito-bypassing fingerprinting is difficult to prevent, unless you use something like uMatrix to disallow JavaScript from everything but a few select domains.

This is a collection of random-ish unique-ish attributes. Any collection of such things can be used to track you, like installed fonts, installed extensions, etc. If this were just a set of meaningless encoded random numbers, then it's essentially a kind of cookie, but that's not what it is. This is (claimed to be) a collection of information that's useful and possibly needed by some backends when testing new Chrome features. It tells servers what your Chrome browser supports. The information is probably similar to "optimizeytvids=1,betajsparser=1".

So, the only question is if Google is actually using this to help fingerprint users in addition to the pragmatic use case. It certainly could be used that way, and it's possible they are, but they have so many other ways of doing that with much higher fidelity / entropy if they want to. If this were intended as a sneaky undisclosed fingerprinting technique, I think they would've ensured it was actually 100% unique per installation, with a state space in the trillions, rather than 8000.

Yes, this could be so sneaky that they took this into consideration and made it low-entropy to create plausible deniability while still being able to increase entropy when doing composite fingerprinting, but I think it's pretty unlikely. Also, 99% of the time they could probably just use use Google Analytics and Google login cookies to do this anyway.

Maybe one actually useful non-advertising usage could be reCAPTCHA ? If you read carefully, it says nowhere than there is the limit to 8000. There is this limit of 8000 only if you disable usage statistics / crash reports.

Sorry about that, too late to edit it now. That is an important detail. If there are 32 or more different feature flags, then that's 4 billion unique states, which would be an effective fingerprint.

I still think it's pretty unlikely they're using it in that way or would in the future, and I think Google fuzzing this for those who opt out of telemetry is probably a signal of good faith in this instance. They realize the privacy implications and provide a way to disengage, even if they don't intend to abuse the information.

But of course the potential for abuse always remains. And the potential for (arguably) non-abusive tracking, like the possibility of it being used for bot detection by reCAPTCHA, as you say.

reCAPTCHA is the most abusive type of tracking. Google simply denys you usage of captcha if you do not give them enough personal information. It doesn't matter if you enter the captcha correctly 20 times. It won't let you in.

This is part of the bot detection, though. It's probably not "not enough personal information", it's "this truly seems like it is unlikely to be a legitimate device/person", due to the huge datasets they're working with. Same with Cloudflare and Tor. Once you operate a security service anywhere near that scale, you start to understand there are inherent challenges and tradeoffs like these,

reCAPTCHA increasingly doesn't even give me a captcha. Instead, they simply deny me from even trying; They send this instead of the challenge:

  <div>
    <noscript>
      Please enable JavaScript to
      get a reCAPTCHA challenge.<br>
    </noscript>
    <div class="if-js-enabled">
      Please upgrade to a
      <a href="[1]">supported browser</a>
      to get a reCAPTCHA challenge.
    </div>
    <br><br>
    <a href="[2]" target="_blank">
    Why is this happening to me?</a>
  </div>

They probably don't like my non-standard user agent string and they definitely don't like that I block a lot of their spyware, but reCAPTCHA used to work properly for many years with the same/similar browser configuration.

[1] https://support.google.com/recaptcha/?hl=en#6223828

[2] https://support.google.com/recaptcha#6262736

I mean, if you don't want Google to track you, then you probably shouldn't use their browser...

I believe someone else in the thread stated it's cleared for incognito, don't remember if they meant it's not sent or that it's a new value.

Normally you would only expect to be identified and tracked when using Google services when logged in. The significance of this post is that they would be able to identify and track you across all your usage of that browser installation regardless of if you've logged out, or say in an incognito window.

Ah. So I was missing something. Thanks for clarifying. That is alarming.

Yes you are missing something important. Once they've tied the browser ID to your personal account they can track you across all google properties, even the ones that you didn't log into.

Unless you're running some extension that emulates FF's container tabs or something, it logs you into all G services. It would matter, though, if this header is still sent in incognito sessions.

I still don't understand. When I log into gmail, it logs me into all Google services. If I am worried about being tracked, surely my first mistake is logging in in the first place? Or visiting in the first place? After all, even if I click "log out," I'm only trusting Google that they unlinked the browser state from the account. If I trust them to do that, I don't see why I shouldn't trust them to ignore this experiment flag from Chrome, or at least not use it for tracking. If I don't trust them to avoid using the experiment state, I don't really see how you can trust them for anything.

Anyway, if you're not building Chrome from source, then you have to trust that they aren't putting anything bad in it. And if you are building chrome from source, you can observe that they only send this experiment ID to certain domains, and they already know who you are on those domains anyway.

>If I am worried about being tracked, surely my first mistake is logging in in the first place?

Good luck completing a google captcha without a Google account or using Chrome.

If you browse the internet, they could know what websites are visited by the same person, but not who they are exactly.

If you visit a load of websites, then also log into google, they connect the two and they know what websites were visited by you specifically.

he means they can continue to identify you after you log off

I think the argument is they have other methods like cookies they could also use. The fact you trust them not to use those methods extends to this form of tracking.