Gemini in Google Sheets now shows a source for every cell. A source is not proof, so check it like this

What did Google change in Fill with Gemini?

I will give a little background first. Sheets has an AI function, written =AI("prompt", range), that sends a prompt to Gemini and puts the answer in the cell. Fill with Gemini is the quick way to use this on many rows at once. You fill one cell, drag it down or click Fill, and Gemini does the rest of the column. When your prompt asks about something in the outside world, like a company head office, the function can pull up to date information from Google Search.

The new part is knowing exactly where the answer came from. According to the post by Google, the sources are attributed to each individual cell and they are available in Sheets on the web. The help page for the AI function explains how you can see them. You click into a cell, hover over the content and click Sources.

The rollout is gradual. It started on 20 October 2026 for both Rapid Release and Scheduled Release domains, and Google says it can take up to 15 days to show up. It is on by default for anyone who already has Gemini in Sheets. The plans named in the post are Business Standard and Plus, Enterprise Standard and Plus, Google AI Pro and Ultra, Google AI Pro for Education and the AI Expanded Access add-on.

Google also says processing is faster and more consistent across cells. Their headline number is up to 55 times faster than manual entry on a 500 cell task, and that comes from an internal study by Google with 95 participants using English prompts. I am just repeating it as a claim from Google. I have not timed it, and I have not seen the Sources button on my own account yet, so everything below is built from the pages from Google and how I check any AI output.

Does a source mean the cell is right?

No. Google says plainly that the AI can still make mistakes. The page on how sources work in Google Workspace with Gemini says that even when Gemini shows sources, it can get things wrong. This same page warns that Gemini may cite a document it did not actually use for a claim, and that it can make up a source and present it as fact.

You can think of a source like a receipt handed to you by someone who did your shopping. It tells you which shop they went to, but it does not prove they bought the right thing, or that the price on the receipt matches the shelf. You still have to look in the bag.

For each cell there are really three separate things to check, and the Sources button only answers the first one. You have to see if the link opens a real page. Then you check if the value in the cell is actually written on that page. Finally, you decide if it is the right kind of page, and if it is recent enough to trust for this column.

That third check is the one people skip. A company About page and a five year old directory listing can both be real pages that both mention a city. Only one of them is a good source for where the company is today. For anything that changes, like a price, a job title or an office address, the date on the page matters just as much as the words on it.

How do I check a column that Gemini filled?

You do not need to check every cell by hand, because then the AI saved you nothing. But you also cannot check three random cells and call the entire column good. What I do with any AI column, and what I would do with this one, is split the rows into the ones that matter and the rest.

1. 01
   Add a status column next to the AI column

   Call it Checked and leave it empty. Every row you verify gets OK, WRONG or NO SOURCE, and a short note if you fixed it.
2. 02
   Check every row a decision depends on

   If a value goes into a client report, decides who you contact, or feeds a total, open its source. These rows are not sampled. They are all checked.
3. 03
   Then check a spread of the rest

   Pick rows from the top, the middle and the bottom of the column, not just the first screen. Gemini fills many cells per request, so a problem can sit anywhere in the list.
4. 04
   Ask the three questions for each one

   Does the link open, is the value on the page, and is it the right page and recent enough. A cell that fails any of the three is marked WRONG or NO SOURCE, not OK.
5. 05
   Widen the check when you find a wrong cell

   One wrong cell in your spread tells you the prompt or the sources are weak for this kind of row. Check more rows, or rewrite the prompt and fill again, before you trust the rest.

The status column is the part I would not skip. It turns a vague feeling of having looked at some rows into something you can clearly show. When a client asks where a number came from, you can point at the row, the source and the word OK right next to it.

This is the exact same habit I use for numbers that an AI puts in a sheet, and I explain the formula side of that in how to check the numbers an AI put in your spreadsheet. Web facts are harder than sums, because there is no formula that proves a city name. The source page is the only real check you have, and this is why opening it matters so much.

How many cells can Fill with Gemini do at once?

The post from Google says one request can now fill up to 3,000 cells. But on 29 October 2026, the AI function help page still says that when you select multiple AI cells, only the first 350 selected cells are generated, and you then wait and select more. These two pages may simply be out of step during the rollout, but you should not guess which limit applies to your own account.

The safe habit is to just count them. After a fill, you check how many cells in the column actually have an answer, using something like =COUNTA(C2:C3001) on the AI column, and compare that with the number of rows you selected. If the count stops short, the rest of the column is simply empty and it needs another run.

A few more limits from the help page matter for checking. The AI function returns text only, so a year or a price comes back as text and needs converting before you add it up. You cannot undo or redo the function itself, so regenerating through Refresh and Insert is the only way to change an answer. Also, when the cells a prompt refers to change later, Sheets does not always prompt you to refresh, so an AI column can quietly go out of date. I wrote about that button-not-formula behaviour in what the AI functions in Google Sheets really do.

When should I not use Gemini to fill a column from the web?

Fill with Gemini is good for rough research where a wrong cell just costs you a few minutes. It suits a first pass on which companies in a list have an office in a given city, or a short description of what each company does. You check the rows you will act on, and the rest of the rows just help you sort.

I would never use it as the final source for anything you send out as a fact. Contact details are the clearest case for this. If you are building a lead list, an email address or a phone number must come from a page you opened yourself, and I explain exactly why in how to build a verified lead list for free. An AI that shows a source for an email address has still not proven that the address works, or that it belongs to the right person.

The same goes for prices, laws, dates of events and anything a client will quote back to you. For those things, you use the AI column to find the page, and then you copy the value from the page yourself. That way the source and the value can never disagree. Your own company data is a different case, because the web is the wrong source for it. If that data sits in BigQuery, Gemini can now answer from it inside a connected sheet, and I wrote up the cost and sharing settings to check first in Gemini in Google Sheets with BigQuery.

How do I freeze a checked AI column before sharing it?

Once the rows that matter say OK, you freeze what you checked. Copy the AI column and paste it next to it with Paste special, Values only, and then add the date you checked it in the header, like Head office (checked 29 Oct 2026). That plain column is what goes into your report or straight to the client.

The reason is simple. A pasted value cannot be regenerated by accident, so the value you checked is the value that stays there. Keep the original AI column with its sources in a separate tab, so you can still click back to the source for any row later. I have not tested whether the Sources link survives a Paste values only, so I would not rely on it surviving.

If the sheet will be opened by people who do not know any of this, a one line note at the top is enough. Just say which column was filled by Gemini and how many rows were checked. It is honest, and it saves the next person from trusting a column more than you did.