What Changed
Google first described the Privacy Sandbox in August 2019 as a set of proposals for advertising without cross-site tracking. It argued that simply blocking cookies, as other browsers had started to do, pushed trackers toward fingerprinting, which people can't clear, and cut publishers' main source of funding.1
In a January 2020 post on the Chromium Blog, it attached a deadline: Chrome would make third-party cookies obsolete "within two years", once the replacements could support interest targeting and conversion measurement.2,3
Chrome tightened its cookie rules in the meantime. From Chrome 80 in February 2020, cookies that didn't say otherwise were treated as first-party only, and cookies meant for cross-site use had to be explicitly marked SameSite=None; Secure.4 That broke some ad tags that hadn't been updated, but it didn't stop cross-site tracking.
Chrome also set out to reduce the other details browsers give away. Between 2022 and 2023 it froze most of the User-Agent string, the description of the browser and device sent with every request: the browser's minor version became 0.0.0, desktop operating system versions became fixed values, and on Android the device model was replaced with "K".5 Sites that need those details now have to ask for them through User-Agent Client Hints, which Google said would minimize covert tracking.6 One side effect for analytics: reports of device models and exact browser versions became less precise for Chrome traffic.
Chrome was, and is, the world's most-used browser, with about two-thirds of browsing worldwide.7 Safari and Firefox already restricted third-party cookies, so Chrome's announcement suggested that cross-site cookies would soon disappear almost everywhere.
Why It Mattered
The announcement set the agenda for the ad industry for the next five years. Ad tech companies built alternative identifiers, publishers invested in logins and first-party data, and advertisers were told to prepare for a "cookieless" future.
It also drew regulators in. Rivals argued the plan would favour Google's own ad business, and the UK's competition regulator investigated.8
The plan never happened. After three delays, Google dropped it in July 2024.
Notes
- Justin Schuh, “Building a More Private Web,” The Keyword, Google, August 22, 2019, https://blog.google/products-and-platforms/products/chrome/building-a-more-private-web/. ↩
- Justin Schuh, “Building a More Private Web: A Path towards Making Third Party Cookies Obsolete,” Chromium Blog, January 14, 2020, https://blog.chromium.org/2020/01/building-more-private-web-path-towards.html. ↩
- Frederic Lardinois, “Google Wants to Phase Out Support for Third-Party Cookies in Chrome within Two Years,” TechCrunch, January 14, 2020, https://techcrunch.com/2020/01/14/google-wants-to-phase-out-support-for-third-party-cookies-in-chrome-within-two-years/. ↩
- “Developers: Get Ready for New SameSite=None; Secure Cookie Settings,” Chromium Blog, October 23, 2019, https://blog.chromium.org/2019/10/developers-get-ready-for-new.html. ↩
- “User-Agent Reduction,” The Chromium Projects, accessed October 17, 2026, https://www.chromium.org/updates/ua-reduction/. ↩
- “Improving User Privacy and Developer Experience with User-Agent Client Hints,” Chrome for Developers, accessed October 17, 2026, https://developer.chrome.com/docs/privacy-security/user-agent-client-hints. ↩
- “Browser Market Share Worldwide,” Statcounter Global Stats, accessed October 19, 2026, https://gs.statcounter.com/browser-market-share. ↩
- Competition and Markets Authority, “CMA to Keep ‘Close Eye’ on Google as It Secures Final Privacy Sandbox Commitments,” GOV.UK, February 11, 2022, https://www.gov.uk/government/news/cma-to-keep-close-eye-on-google-as-it-secures-final-privacy-sandbox-commitments. ↩