Prefill and token generation speed

Qwen3.8 27B on RTX 4090: prefill and generation

Watch Qwen3.8 27B process input and respond on an RTX 4090 24GB. Compare with an RTX 3090 to see how waiting time differs despite the same 24GB memory capacity.

Benchmark-based estimate · 4K input · one user

Last updated

38.3 ~ 51.9 tok/sDecode speed
Model fully loaded (17.56GB / 22.5GB)
First token (TTFT)
2.6 to 3.6 secondsContext 4,096 input tokens included
Prefill speed
1,141 ~ 1,591 tok/s2.6 to 3.6 seconds (Estimation based on public benchmarks)
Total time (E2E)
Approximately 4.8 to 6.6 seconds117 output tokens included
Press Play to process the input and generate the answer.
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1008 GB/s
27B
Expand settings 4-bit · 4K · Baseline decode
QuantizationNeed 17.56GB
Input context4K tokens
Baseline
Baseline
Sample question:
117 output tokens

Reading this result

The 4090 also has 24GB of VRAM, so distinguish capacity from processing speed. The right comparison depends on whether you need a larger model or faster execution of one that already fits.

Required / available memory
17.6GB / 22.5GB
Runtime
llama.cpp CUDA · Q4_K_M

Compare this model side by side

When comparing with a 3090, check document prefill as well as short chat. These are LLM results; the same ratio does not establish image or video generation performance.

Check configuration

RTX 4090 24GB · Memory 24GB

Qwen3.8 27B Q4_K_M configuration. Check that the retailer lists the same memory option.

What changes with a longer document?Expand input length, waiting time, speed and memory
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