Am Thu, 1 Oct 2020 22:47:31 -0500 schrieb Don Hosek:

> While looking into this question https://tex.stackexchange.com/questions/565031/slightly-bigger-integral-in-exponent <https://tex.stackexchange.com/questions/565031/slightly-bigger-integral-in-exponent> I found that the formatting of \int differs slightly when using the amsmath package vs the base LaTeX with the former using a scriptstyle integral while the base uses a textstyle integral.

> So the questions are: (1) what¢s happening differently in amsmath
> to change the appearance of the integral

amsmath use a different cmex font:

cmextra/cmex7.pfb instead of cmex10.pfb because of this code part

\ifnum\cmex@opt=7 \relax
\DeclareFontShape{OMX}{cmex}{m}{n}{%
<-8>cmex7<8>cmex8<9>cmex9%
<10><10.95><12><14.4><17.28><20.74><24.88>cmex10%
}{}%
\expandafter\let\csname OMX/cmex/m/n/10\endcsname\relax
\else

you can get the "classical" appearance with

\usepackage[cmex10]{amsmath}

> and (b) which is the correct behavior?

Well like always, it is a matter of taste, but I would say they made
the change because they think it looks better like this and I agree.

--
Ulrike Fischer
http://www.troubleshooting-tex.de/