Will an Assembler program run on processors from the same company?

Question

assembler

Now I'm looking at different Assemblers and the question arose:
Will a program written for 80286 work on Pentium (1,2,3,4)? And will a program written for Pentium work on Core i3/i5/i7/i9/x ? Or even for different "cows" the code is different?
If not, how much will the code need to be rewritten?
Or is there still a difference in the code, only if you use different architectures (x86 / x64)?

Answer 1

If there are no specific MMX / SSE in the code (and they are far from always needed), then it will work.
32/64 - will work because all 64 bit x86 families support 32 bits
It's not called
x86, but AMD64