Which Intel "generation" is my Mac's CPU?

You can get the processor generation by running the following command in Terminal:

sysctl machdep.cpu.brand_string

If the output contains a dash and a number after your "iX"-Core model, the first digit after the slash is the processor generation. See: Intel® Processor Numbers: Laptop, Desktop, and Mobile Device

Examples:

• 2nd Generation : Intel(R) Core(TM) i5-2760QM
• 5th Generation : Intel(R) Core(TM) i7-5257U CPU @ 2.70GHz
• 6th Generation : Intel(R) Core(TM) m3-6Y30
• 8th Generation : Intel(R) Core(TM) i5-8350U

If the dash is missing, it's first generation (or a different CPU altogether), e.g.:

• 1st Generation : Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz

Different approach:

sysctl machdep.cpu

Gives you detailed CPU information.

From machdep.cpu.extmodel:

• 0 for a "Intel(R) Core(TM)2 CPU T7400 @ 2.16GHz"
• 1 for a late 2009 iMac-i5 "Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz"
• 1 for a Mac Pro (Mid 2010) "Intel(R) Xeon(R) CPU W3530 @ 2.80GHz"
• 4 for a 2015 macbook pro (4th generation)
• 4 for a "Intel(R) Core(TM) i7-4770HQ CPU @ 2.20GHz" (4th generation)

Although it's inconsistent:

• 4 for a 2016 macbook "Intel(R) Core(TM) m3-6Y30" (6th generation)
• 5 for a "Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz" (6th generation)

From fsb's comment below:

According to Intel, the generation is the first number after the "-" (in machdep.cpu.brand_string)