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

> While looking into this question <> 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
  \expandafter\let\csname OMX/cmex/m/n/10\endcsname\relax

you can get the "classical" appearance with 


> 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