Here's roughly what it picks today from my testing:

- 8 GB Mac (M1/M2): Gemma 4 E2B

- 16 to 18 GB Mac: Gemma 4 E4B

- 24 to 64 GB Mac: Gemma 4 26B A4B

- 128 GB Mac Studio: gpt-oss 120B

- Windows/Linux with an RTX 3060 or 4070 (12 GB) and 32 GB RAM: Gemma 4 26B, split between the GPU and system memory

- RTX 4090: Gemma 4 26B fully on the GPU

- No GPU, 16 GB RAM: a compressed Gemma 4 E4B on the CPU

High level, it looks at your memory and memory bandwidth and then picks the smartest one that stays above about 15 tokens a second with room for a decent context.