Despite what its naming suggests, the Intel 8008 was developed independently of the [[Intel 4004]]. They were separate projects with distinct architectures and purposes, not a progression or derivative of one another.
See: [https://www.righto.com/2016/12/die-photos-and-analysis-of_24.html Die photos and analysis] [https://www.righto.com/2017/02/reverse-engineering-surprisingly.html The ALU] [https://www.righto.com/2017/03/analyzing-vintage-8008-processor-from.html The counters] [https://www.righto.com/2020/11/reverse-engineering-carry-lookahead.html The carry lookahead circuit] Reverse engineering of the 8008 microprocessor
Fun fact: Before microprocessors were invented, there was already ALU chips, like the 74181 ALU chip, that were used in CPU boards. [https://www.righto.com/2017/01/die-photos-and-reverse-engineering.html Source ]