LATEST ENGINEERING NOTE · 2026.09.17 Performance Optimization

DeepSeek V4.1 Flash Engineering, Part 4: Long Prefill and the Final Optimization Mile

Once DeepSeek V4.1 Flash could run, the harder problem was keeping 261K and eventually one million cold input tokens moving while preserving official sparse semantics and complete output. This final article follows the real long-prefill bottlenecks through cross-layer candidate selection, lossless integer indexing, one-time expansion, dynamic LDS, dense tiling, chunk sizing, and arena reuse. It reports the retained 1,553.91-token/s long-input result, a complete one-million-token run, and current single- and eight-request decode throughput.

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ZLLM VISION

Building the Best Inference Engine

Rust-nativeOwnership and types protect memory and concurrency safety without giving up hardware-level performance.
Unified architectureA clear, orthogonal decomposition of Model, Runtime, Backend, Kernel, and Algorithm unifies development and optimization across CPU, GPU, and NPU.
Every scaleOne inference stack spanning resource-constrained embedded devices to hyperscale clusters.
Engineering

Why Did One Sentence Consume Hundreds of Thousands of Tokens?

A short prompt to Claude Code or Codex may carry tens or hundreds of thousands of tokens of hidden working context. This article explains the three major HTTP APIs, prefix-cache hits, VRAM-to-SSD backup, and token-level tool-call fences.