M4 is built with TSMC's 2nd Gen 3nm process. M3 is on the 1st gen 3nm.

For the base M3 vs base M4:

- the CPU (4P+4E) & GPU (8) core counts are the same

- NPU perf is slightly better for M4, I think, (M4's 38TOPS @ INT8 vs M3's 18TOPS @ INT16)

- Memory Bandwidth is higher for M4 (120 GB/s vs 102.4 GB/s)

- M4 has a higher TDP (22W vs 20W)

- M4 has higher transistor count (28B vs 25B)