Gdtyjr

This Wikipedia page says the following:

Most x86 processors since the Intel 80486 have had these x87
instructions implemented in the main CPU

So the above quote means that some CPUs that were realeased after the Intel 80486 CPU did not have the x87 floating-point unit built in.

But what was the last CPU that did not have the x87 floating-point unit built in?

All Intel x86 CPUs since the 80486 line have included floating point instructions, i.e. everything from the Pentium* onwards. So the last Intel processor to lack an on-board floating-point unit (FPU) was the 80486SX (and the embedded 80486GX).

Other manufacturers, who made 486-compatible processors, continued making non-FPU chips, aiming for the budget market. These include Cyrix's Cx486SLC, and AMD's AM486SX. A 66MHz version of the latter, the Am486SX2-66, was released in 1994, a year after Intel had released its first Pentium processor.

In order to compete with the Pentium range, third-party manufacturers effectively had to include an on-board FPU, so there were no "586" chips without floating-point instructions.

I expect that the last manufactured x86 CPU that lacked floating-point instructions will have been an embedded chip such as the 80486GX.

* for further reading, see the Pentium FDIV bug

As far as I’m aware, the last FPU-less x86-compatible CPU is the Vortex86SX, released in 2007 and still available now. This is a Pentium-class CPU, capable of running any Pentium code which doesn’t require an FPU.