Cite a source please.

You can literally just Google this, there are many sources. Literally the top of the Google results:

[1] https://www.politico.com/news/2025/03/21/trump-boeing-stealt...

[2] https://www.usnews.com/news/national-news/articles/2025-03-2...

The exact transcript is here:

[3] https://rollcall.com/factbase/trump/transcript/donald-trump-...

All of these are in the top-10 first results when you search for this.

All of those links appear to be discussing the F-47 and this thread is discussing the F-35.

To be fair, the exact sentence is "we like to tone them down about 10%", which suggests a more common practice rather than only a plan specifically for the F-47.

Of course it's also a quote from Trump, so who knows how much of it is from his random sentence generator. Although I'd guess he's quoting another official or someone from the defence industry.

10% of what? Are they 10% smaller?

This is very common for export variants of a high end military products.