[Doc] V1 user guide

docs/source/getting_started/v1_user_guide.md

@@ -0,0 +1,53 @@
+# vLLM V1 User Guide
+
+## Why vLLM V1?
+Previous blog post [vLLM V1: A Major Upgrade to vLLM's Core Architecture](https://blog.vllm.ai/2025/01/27/V1-alpha-release.html)
+
+## Semantic changes and deprecated features
+
+### Logprobs
+- vLLM V1 now supports both sample logprobs and prompt logprobs, as introduced in this [PR](https://github.com/vllm-project/vllm/pull/9880).
+- **Current Limitations**: 
+  - V1 prompt logprobs do not support prefix caching.
+  - V1 logprobs are computed before logits post-processing, so penalty 
+  adjustments and temperature scaling are not applied.
+- The team is actively working on implementing logprobs that include post-sampling adjustments.
+
+### The following features has been deprecated in V1:
+
+#### Deprecated sampling features
+- best_of
+- logits_processors
+- beam_search
+
+#### Deprecated KV Cache features
+- KV Cache swapping
+- KV Cache offloading
+
+## Unsupported features
+
+- **LoRA**: LoRA works for V1 on the main branch, but its performance is inferior to that 
+  of V0.
+  The team is actively working on improving the performance [PR](https://github.com/vllm-project/vllm/pull/13096).
+
+- **Spec Decode other than ngram**: currently, only ngram spec decode is supported in V1 
+  after this [PR](https://github.com/vllm-project/vllm/pull/12193).
+
+- **Quantization**: For V1, when the CUDA graph is enabled, it defaults to the 
+  piecewise CUDA graph introduced in this [PR](https://github.com/vllm-project/vllm/pull/10058) ; consequently, FP8 and other quantizations are not supported. 
+
+- **FP8 KV Cache**: FP8 KV Cache is not yet supported in V1.
+
+## Unsupported models
+
+All model with `SupportsV0Only` tag in the model definition is not supported by V1. 
+
+- **Pooling Models**: Pooling models are not supported in V1 yet.
+- **Encoder-Decoder**: vLLM V1 is currently limited to decoder-only Transformers. 
+  Please check out our 
+  [documentation](https://docs.vllm.ai/en/latest/models/supported_models.html) for a 
+  more detailed list of the supported models. Encoder-decoder models support is not 
+  happending soon. 
+
+
+## FAQ

docs/source/index.md

@@ -67,6 +67,8 @@ getting_started/quickstart
 getting_started/examples/examples_index
 getting_started/troubleshooting
 getting_started/faq
+getting_started/v1_user_guide
+
 :::
 
 % What does vLLM support?