Guide
KV cache quantization halves the cache — and on the 7900 XTX it made generation faster
At 65.5k context a 27B model wants nearly 6 GB for its KV cache, on top of 16 GB of weights. llama.cpp and other tools let you quantize it. Thirteen runs on one card at f16, q8_0, q5_0 and q4_0: the cache halves, generation gets faster, and no quality cost shows up at all.
- At 65.5k context the KV cache is 5.9 GB — more than a third the size of the model's own 16.2 GB of weights. q4_0 halves it to 2.9 GB.
- Measured VRAM fell from 24.8 GB to 22.1 GB across the sweep, so the saving lands on the card and not just in the estimate.
- No measurable quality cost. Overall medians land at 86.1 (f16), 88.7 (q8_0), 87.4 (q5_0) and 87.6 (q4_0), and every range overlaps every other. The untouched default scores lowest of the four.
- Generation is faster, and this one holds up: 40.4 tok/s at f16 against 51.7 at q8_0, with the f16 runs (38.8-42.4) not overlapping q8_0 (50.5-52.1) or q4_0 (50.2-54.9) at all.