Implementing a Modern LLM in 700 Lines of C
Critical_Physics8 · reddit · 2026-08-28
The author released gemma4.c, implementing the full inference runtime for Google's Gemma 4 E2B model in approximately 700 lines of C.
Project Features:
- Single-file implementation, no external dependencies, easy to read
- Implements tokenizer, Transformer, KV cache, sampling, and CPU kernels from scratch
- Designed to help developers understand the code-level details of LLM inference
Performance Optimizations:
- Int8 weights and activations quantization
- OpenMP parallelization
- AVX2 and AVX-512 VNNI instruction set support
Benchmarks (Ryzen 7 7700):
- Prefill: 639 tok/s (512 tokens)
- Generation: 25.9 tok/s
- Outperforms llama.cpp
GitHub Repo
Related event: Gemma 4 Inference Runtime Implemented in 700 Lines of C(2 posts)→
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