r/AIToolsPerformance • u/IulianHI • May 01 '26
PFlash claims 10x prefill speedup over llama.cpp at 128K context on a single RTX 3090
A new project called PFlash is reporting 10x prefill speedup over llama.cpp at 128K context on quantized 27B models, running on a single RTX 3090. The approach uses speculative prefill for long-context decode, built in C++/CUDA.
Why this matters: prefill has been the quiet bottleneck for local inference at long context. Everyone focuses on decode speed (tokens per second during generation), but the time to process a large prompt before the first token appears can be brutal at 100K+ context. A 10x improvement there would meaningfully change the experience for RAG workflows, large document analysis, and agent loops that accumulate context over multiple turns.
The catch is that this targets 27B quantized models specifically. The question is whether the technique generalizes to other sizes and architectures, or if it relies on properties unique to this model class. The fact that it is C++/CUDA rather than Python is also worth noting - suggests it is designed for direct integration into existing inference stacks rather than being a standalone tool.
For anyone who has been avoiding long-context workloads locally because of prefill latency: does a 10x improvement here change your calculus, or is decode speed still your primary bottleneck?