Contents
- Zero months, 18 months, or no number at all — the short answer
- What we checked ourselves, and when
- What Mozilla and Mistral announced on September 16
- Firefox Smart Window's retention promise: zero, with no ceiling attached
- Google Gemini's 18-month default hides a 3-year catch
- Microsoft Copilot: one page says 18 months, the other says nothing
- Why you can't stack these three numbers side by side
- FAQ: quick answers
Firefox Smart Window, Google’s Gemini, and Microsoft’s Copilot in Edge all promise to protect what you type into them. None of them measure that promise the same way. Mozilla and Mistral use the phrase “zero data retention” with no number attached to it at all. Google states an 18-month default that can stretch to three years for chats a human reviewer opens. Microsoft states 18 months on one official page and nothing on another. My take: that’s not a rounding error — it’s three different definitions of privacy wearing the same word.
Zero months, 18 months, or no number at all — the short answer
Here’s the short version, checked against each company’s own page on September 18, 2026:
- Firefox Smart Window (powered by Mistral): zero data retention, no numeric window disclosed anywhere
- Google Gemini Apps: 18 months by default, adjustable to 3, 36, or indefinite — but up to 3 years for chats a human reviewer looks at
- Microsoft Copilot (consumer app, older version): 18 months by default
- Microsoft Copilot Chat in Edge (Entra/enterprise): no retention number published on its own Learn page at all
That’s four different disclosures, not one shared standard. The rest of this piece walks through what each company’s own words actually say, and where the comparison between them breaks down.
What we checked ourselves, and when
These aren’t summaries of the policies. Each company’s own policy or announcement page — Mistral’s partnership announcement, Mozilla’s own Smart Window blog post, Google’s Gemini Apps Privacy Hub support page, and Microsoft’s Copilot Privacy FAQ plus its separate Edge-specific Learn page — was checked directly on September 18, 2026, with the exact retention language pulled word for word. It’s the same direct-to-source habit worth applying before trusting whether a Google ad is actually legitimate at face value.
| Product | Official source | Exact stated retention term | Numeric ceiling |
|---|---|---|---|
| Firefox Smart Window (Mistral) | mistral.ai/news/mistral-x-mozilla/ (published Sept. 16, 2026) | “conversations aren’t saved on Mozilla’s servers by default, and partners like Mistral agree to zero data retention” | None disclosed — a qualitative promise, no day or month figure given |
| Google Gemini Apps | support.google.com/gemini/answer/13594961 | Auto-delete default of 18 months, adjustable to 3, 36, or indefinite | 18 months default; human-reviewed chats “retained for up to three years”; even Keep Activity-off chats persist 72 hours |
| Microsoft Copilot (consumer) | support.microsoft.com — Copilot Privacy FAQ | “By default, we store conversation activity for 18 months” | 18 months — but the same page says it applies only to “the older version” of the app, before the Aug. 18, 2026 update |
| Copilot Chat in Edge (Entra/enterprise) | learn.microsoft.com/en-us/copilot/edge | No retention figure stated; page points to “enterprise data protection” and Purview/DLP policies instead | Not disclosed on this page at all |
These are four separate documents from three companies — not one comparison table any of them publishes itself. So “Edge Copilot’s retention period” genuinely depends on which Microsoft page, and which Copilot product, you land on. Firefox and Mistral’s “zero retention” isn’t directly comparable to a month figure, either: it describes what the model provider does with data in transit, not how long anything sits on Mozilla’s own servers.
What Mozilla and Mistral announced on September 16
Mozilla and Mistral announced their partnership on September 16, 2026. Firefox Smart Window — Mozilla’s AI browsing assistant, currently in beta — is now powered by Mistral’s models. The feature is built to:
- Handle complex searches
- Remember pages you’ve already clicked on
- Pull context from tabs you already have open
The rollout starts narrow. It’s live now in:
- France
- The United States
- Canada
Mozilla and Mistral say the UK and Germany are next, sometime later in 2026. Mistral describes its models as fine-tuned for regional languages, dialects, and cultural context.
One detail is softer than the headlines suggest. TestingCatalog’s article headline names “Mistral Small 4” as the model behind Smart Window, but the body of that same article doesn’t actually confirm a specific model or version. Mistral’s own announcement separately lists four current models — Mistral OCR 4, Mistral Medium 3.5, Mistral Small 4, and Voxtral TTS — without saying which one, if any, is the one running inside Firefox. Which model Smart Window actually calls is not confirmed as of this writing.
Firefox Smart Window’s retention promise: zero, with no ceiling attached
Mistral’s own announcement states the policy plainly: “conversations aren’t saved on Mozilla’s servers by default, and partners like Mistral agree to zero data retention.” That’s the entire disclosure. There’s no day count, no month count, no window — just a qualitative promise.
One claim keeps showing up in secondary coverage: that Mozilla’s proxy hides a user’s IP address and device ID from Mistral. It isn’t there. Neither Mistral’s announcement nor Mozilla’s blog post uses that language, so we’re leaving it out rather than repeating it as fact.
One line covers what’s missing: how long anything sits in a cache or a log on Mozilla’s side, even briefly, isn’t addressed anywhere in either post.
Zero retention sounds like the strongest privacy stance of the three, and on paper it is. But a policy with no number attached is also a policy nobody can check against a clock. That’s worth remembering before treating “zero” as automatically stricter than Google’s 18 months. Anyone who’d rather skip that trust question entirely can look at local AI tools that don’t phone home at all.
Google Gemini’s 18-month default hides a 3-year catch
Google’s support page states the default plainly: “Your activity is auto-deleted after 18 months.” Users can change that window to:
- 3 months
- 18 months (the default)
- 36 months
- Indefinite — never auto-delete
That default undersells the real ceiling, though. Chats pulled into human review are retained separately for up to three years, regardless of what a user set their auto-delete window to. Google states that chats reviewed by human reviewers aren’t deleted when a user deletes their activity — instead, per Google’s own wording, they’re “retained for up to three years.” Even chats made with Keep Activity switched off, or temporary chats, still stick around for a minimum of 72 hours for service delivery.
Google doesn’t disclose what share of conversations actually get routed to human review. Without that number, there’s no way to estimate how often the three-year ceiling applies versus the 18-month default shown on the settings screen. That’s a real gap in the disclosure, not a footnote. To be fair to Google, publishing an exact review rate could itself leak information about how its moderation works — but that doesn’t make the gap disappear.
Eighteen months is the number that shows up in the settings screenshot everyone shares. Three years is the number that matters if a reviewer ever opens your chat.
Microsoft Copilot: one page says 18 months, the other says nothing
Microsoft’s consumer-facing Copilot Privacy FAQ gives a number: “By default, we store conversation activity for 18 months.” Read further down the same page, though, and that number comes with carve-outs the headline figure doesn’t mention:
- It doesn’t cover the updated Copilot app version that shipped on August 18, 2026 — the FAQ says its 18-month figure applies only to “the older version of the Microsoft Copilot app”
- It “does not apply to the use of Microsoft 365 Copilot when signed in with Entra ID”
Users can delete individual conversations or their entire history from within the app; the FAQ itself doesn’t use any specific dashboard name for that control.
Then there’s the Edge-specific page. Microsoft’s own Learn documentation for Copilot Chat in Edge, last updated August 18, 2026, gives no retention number anywhere on the page. Instead it points to “enterprise data protection” for users signed in with a Microsoft Entra account, backed by Purview, Intune MAM, and Microsoft Defender for Cloud Apps. That same page notes only “summarized content,” not the full webpage, gets handled under enterprise protection — and if a user agrees to share page context, the URL, page title, query, and prior chat history all get passed into Copilot Chat.
Microsoft hasn’t published a retention number for the app version that replaced the old one on August 18, 2026.
Why you can’t stack these three numbers side by side
Add it up and you get zero, 18 months, three years, and no number at all — but stacking those four in one sentence overstates how comparable they really are.
Microsoft’s two pages aren’t one policy; they’re two different Copilot products, the consumer app and the Entra-signed-in Copilot Chat in Edge, documented on two pages that don’t cross-reference each other. Same company, two different answers. Firefox and Mistral’s “zero retention” describes what happens to data while a model provider is processing it in transit, not a stored-conversation duration on Mozilla’s own servers — which is what Google’s and Microsoft’s month counts actually describe. And Google’s three-year ceiling only kicks in for the subset of chats pulled into human review, a subset Google won’t size.
My honest read: these three companies aren’t competing on the same axis, and lining them up like a spec sheet is closer to comparing apples to a policy document. Anyone picking a browser assistant on privacy grounds alone should treat “zero,” “18 months,” and “no number” as three different kinds of answers to three slightly different questions, not three points on the same scale.
FAQ: quick answers
Does Firefox Smart Window send my data to Mistral’s servers? Yes — Mistral’s models process the conversation, and Mistral has agreed to zero data retention on those requests, according to Mistral’s own announcement. Neither company’s post spells out how long anything might sit in a cache or log on Mozilla’s side before that.
Is Google Gemini’s 18-month default the longest my chats can be kept? No. Eighteen months is only the default auto-delete window. Chats pulled into human review are kept separately for up to three years, per Google’s support page — and Google hasn’t said how often that actually happens.
Does Microsoft’s 18-month figure apply to Copilot Chat in Edge? That’s not clear. The 18-month number comes from Microsoft’s general Copilot Privacy FAQ, which says it applies to “the older version” of the consumer app, not to Entra-signed-in use. The Edge-specific Learn page for Copilot Chat in Edge gives no retention number at all — it defers to enterprise data-loss-prevention policies instead.
None of this makes the choice obvious. Firefox’s promise is the simplest to state and the hardest to verify — there’s no number to hold anyone to. Google’s is the most detailed of the three, and also the one with the widest exception attached. Microsoft’s is the most literally contradictory: two official pages from the same company, answering the same question two different ways. If your own browser’s controls won’t cooperate in the meantime, it helps to know how to fix privacy settings that are greyed out or locked. Worth watching from here: whether Microsoft ever publishes a retention figure for the Copilot app version that replaced the old one in August, and whether Google ever discloses what share of chats actually reach a human reviewer. Until either happens, the honest comparison is the table above — not a single winner.
Image credits
- Photo by Zulfugar Karimov on Unsplash
- Le Chat by <p><b>Oprogramowanie:</b> Mistral AI
</p> <b>Zrzut ekranu:</, licensed under PUBLIC DOMAIN (via Openverse)
- Copilot PC by <a href=”//commons.wikimedia.org/wiki/User:%CE%9A%CE%9A_%CE%, licensed under CC BY-SA 4.0 (via Openverse)