Speculative Decoding in vLLM: Complete Guide to Faster LLM Inference
· 34 min read

Introduction
Ever waited for an AI chatbot to finish its answer, watching the text appear word by word slow? It can feel painfully slow, especially when you need a fast response from a powerful Large Language Model (LLM).
The big problem is in how LLMs generate text. They don't just write a paragraph all at once; they follow a strict, word-by-word approach.
- The model looks at the prompt and the words it has generated so far.
- It calculates the best next word (token).
- It adds that word to the text.
- It repeats the whole process for the next word.
Each step involves complex calculations, meaning the more text you ask for, the longer the wait. For developers building real-time applications (like chatbots, code assistants, or RAG systems), this slowness (high latency) is a major problem.