Add the speculation docs.

docs/source/conceptual/speculation

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-## Speculation

docs/source/conceptual/speculation.md

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 ## Speculation
+
+Speculative decoding, assisted generation, Medusa, and others are a few different names for the same idea.
+The idea is to generate tokens *before* the large model actually runs, and only *check* if those tokens where valid.
+
+So you are making *more* computations on your LLM, but if you are correct you produce 1, 2, 3 etc.. tokens on a single LLM pass. Since LLMs are usually memory bound (and not compute bound), provided your guesses are correct enough, this is a 2-3x faster inference (It can be much more for code oriented tasks for instance).
+
+You can check a more [detailed explanation](https://huggingface.co/blog/assisted-generation).
+
+Text-generation inference supports 2 main speculative methods:
+
+- Medusa
+- N-gram
+
+
+### Medusa
+
+
+Medusa is a [simple method](https://arxiv.org/abs/2401.10774) to create many tokens in a single pass using fine-tuned LM heads in addition to your existing models.
+
+
+You can check a few existing  fine-tunes for popular models:
+
+- [text-generation-inference/gemma-7b-it-medusa](https://huggingface.co/text-generation-inference/gemma-7b-it-medusa)
+- [text-generation-inference/Mixtral-8x7B-Instruct-v0.1-medusa](https://huggingface.co/text-generation-inference/Mixtral-8x7B-Instruct-v0.1-medusa)
+- [text-generation-inference/Mistral-7B-Instruct-v0.2-medusa](https://huggingface.co/text-generation-inference/Mistral-7B-Instruct-v0.2-medusa)
+
+
+In order to create your own medusa heads for your own finetune, you should check own the original medusa repo. [https://github.com/FasterDecoding/Medusa](https://github.com/FasterDecoding/Medusa)
+
+
+In order to use medusa models in TGI, simply point to a medusa enabled model, and everything will load automatically.
+
+
+### N-gram
+
+
+If you don't have a medusa model, or don't have the resource to fine-tune, you can try to use `n-gram`.
+Ngram works by trying to find in the previous sequence existing tokens that match, and use those as speculation.
+
+This is an extremely simple method, which works best for code, or highly repetitive text. This might not be beneficial, if the speculation misses too much.
+
+
+In order to enable n-gram speculation simply use
+
+`--speculate 2` in your flags.
+
+[Details about the flag](https://huggingface.co/docs/text-generation-inference/basic_tutorials/launcher#speculate)