This answer to the question "What was the rationale behind 36 bit computer architectures?" makes the point that early computers were assembled by hand, rather than having central processing units on one chip. The number of CPU bits were chosen carefully to fulfill the needs of the architecture, rather than necessarily choosing a power of 2. To that end, what was the last central processing unit made commercially available that was not on one chip?
Clarification: To avoid this degenerating into an "anything goes" question, the following functions do not count, even if they occur outside the CPU:
Power regulation, reset conditioning, and clock generation do not count, because it could apply to nearly every computer (except some microcontrollers).
"CPU" implies arithmetic, logic, and control. It specifically does not include memory, nor the interface to memory. Therefore ROM, RAM, bus demultiplexers, bus buffers/transceivers, address decoding, caches, memory management units, northbridges, and mass storage do not count because they are part of the memory system.
Similarly, "CPU" does not include input or output. Thus peripherals and southbridges do not count because they are part of I/O.
Floating-point units and other co-processors do not count, as the CPU could still execute basic programs without them. Notably, co-processors were available and often used with early x86 and 68k processors, yet the CPU was still functional without them.
Using multiple chips to include multiple processors is not the scope of the question.
Any CPU that markets itself as a microprocessor or microcontroller is probably against the spirit of this question, as the intention of a microprocessor is to put the entire CPU on one chip.
As there is already one good answer, the question is certainly answerable.
Because the question is asking for the "last" instance, please include the year that the CPU came to market in your answer.
Related: Was there ever a genuine "mainframe-on-a-chip" microprocessor?