A word to describe a company which other companies measure themselves by

Perhaps you're looking for benchmark.

A standard by which something can be measured or judged

Inflation ... is a great distorter of seemingly fixed economic ideas and benchmarks” (Benjamin M. Friedman).

[American Heritage Dictionary]

Another good choice would be touchstone.

A standard or criterion by which something is judged or recognized.

It is a touchstone against which I measure my own political views.

[Lexico]

An alternative to benchmark is yardstick.

That has the figurative meaning:

A standard to which other measurements or comparisons are judged.

[Wiktionary]

Gold standard is an idiomatic phrase that means essentially what you are looking for here.

Ikea, furniture manufacturer and the "gold standard" in retail, has…

If someone/something is the "gold standard", then they are the leader to which everyone/everything is compared.

It is an obvious reference to the classical monetary system, which uses a fixed quantity of gold as the standard economic unit. All money is ultimately compared against gold, which serves as the standard.

I believe that is probably the closest to the original meaning, even though it is a phrase instead of a single word.

If you absolutely must have a single word, the other answers are acceptable, but I would recommend simply leader.