Earlier quoted context omitted.
> The one thing I would want everyone curious about local LLMs to know is that being able to run a model and being able to run a model fast are two very different thresholds. You can get these models to run on a 128GB Mac, but we need to first tell if Q4 retains enough quality (models have different sensitivities to quantization) and how fast it runs. Very valid. This is an active area of research, and there are a lo…
> - Importance-weighted quantization (e.g. IQ4) also provides way better PPL, KDL, etc. at the same size as a Q4. All the Q quants from big quant providers are importance-weighted (imatrix) nowadays. The main (possibly only?) difference between Q and IQ today is that IQ uses a lookup table to achieve better compression. That is also why IQ suffers more when it can't fully fit into VRAM. It's important to teach people…
- Q4_0 (not K quant) is the traditional flat quantization - Q4_K (4-bit K quant) uses an imatrix and important weights get higher precision (5-6 bits instead of 4, but still largely 4 bits) - IQ4 uses an imatrix and important weights get an optimized scale to avoid clipping at 4-bit, but all the weights are still 4-bit
And yeah most quants nowadays are K quants which are importance weighted