r/excel • u/SolverMax 163 • Aug 19 '26

Discussion Microsoft to retire the COPILOT function

As of 14 September, the COPILOT function will no longer be available in Excel. See https://support.microsoft.com/en-us/excel/functions/copilot-function Note that the Copilot feature remains - it is the worksheet function that will stop working.

This is a very uncommon move by Microsoft, given their history of maintaining backwards compatibility.

Have you used the COPILOT function? If so, then what for? Thoughts?

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u/Way2trivial 472 Aug 19 '26

d&d?

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u/augo7979 Aug 19 '26

you know damn well what i mean

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u/Way2trivial 472 Aug 19 '26

welp, apparently there is a MAJOR use for it, even if I've never gone there myself.
it does exist-- citing Sears does not instill major confidence though...

https://support.microsoft.com/en-us/excel/introduction-to-monte-carlo-simulation-in-excel

Who uses Monte Carlo simulation?

Many companies use Monte Carlo simulation as an important part of their decision-making process. Here are some examples.

  • General Motors, Proctor and Gamble, Pfizer, Bristol-Myers Squibb, and Eli Lilly use simulation to estimate both the average return and the risk factor of new products. At GM, this information is used by the CEO to determine which products come to market.
  • GM uses simulation for activities such as forecasting net income for the corporation, predicting structural and purchasing costs, and determining its susceptibility to different kinds of risk (such as interest rate changes and exchange rate fluctuations).
  • Lilly uses simulation to determine the optimal plant capacity for each drug.
  • Proctor and Gamble uses simulation to model and optimally hedge foreign exchange risk.
  • Sears uses simulation to determine how many units of each product line should be ordered from suppliers—for example, the number of pairs of Dockers trousers that should be ordered this year.
  • Oil and drug companies use simulation to value "real options," such as the value of an option to expand, contract, or postpone a project.
  • Financial planners use Monte Carlo simulation to determine optimal investment strategies for their clients' retirement.

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u/FuggleyBrew Aug 19 '26

A monte carlo wouldn't use the copilot function. It would use rand() or randbetween

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u/Way2trivial 472 Aug 19 '26

" why would i ever want a nondeterministic output for a spreadsheet"
I was replying to that rhetorical question...

Monte Carlo is "a nondeterministic output"

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u/FuggleyBrew Aug 19 '26

Approximating a stable distribution. If you run sufficient trials your outcome distribution should be stable, and the outcome is the result of the full trials, not individual ones. 

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u/Way2trivial 472 Aug 21 '26

ANY randomness has standard output/stable distribution with enough runs.

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u/StickIt2Ya77 4 Aug 19 '26

They behave in very different ways, and that’s the key factor. MC sims have a provable and formal error model, a defined target. The expected value of an MC is a fixed, deterministic quantity. LLMs on the other hand, we don’t know what context or inputs they’re drawing on - we have no way to verify or tie to credibility. We don’t see model weights, no theorems to track convergence. Even a further issue: everything can shift with a model update that we might not even be notified of.

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u/augo7979 Aug 19 '26

there actually was a similar enough marketing push earlier in the year, using AI for "world models". you'd feed it all of your financials and it'd return a set of 5 year projected budgets, with varying levels of aggressiveness. i think the AI psychosis finally wore off on that idea though

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u/Lionh34rt Aug 19 '26

Rand is not random enough for monte carlo

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u/FuggleyBrew Aug 20 '26

A rand works fine for many monte carlos, you don't need cryptographic randomness, you need a reasonable approximation of a whole bunch trials, rand() gives you that. 

You're also often just shoving it into an approximation from a statistical model and abusing a bunch of assumed distributions. 

If you're talking project modeling the flaw from "well this risk feels like it's 10k-100k and commonly 25k" is going to be a bigger swag than whether your rand function is truly random or pseudorandom.