Overview
S4 KV is a KV-cache backend for vLLM v1 paged attention that stores the attention KV cache in int4 instead of fp16, using KIVI-style quantization (per-channel asymmetric int4 for KEY, per-token int4 for VALUE). It is bit-identical to fp16 greedy decoding (verified on Qwen2.5 1.5B/3B/7B and Llama-3.2-3B / 3.1-8B), so you get roughly 3x more KV-cache density: more concurrent requests and longer context on the same GPU, with no measured quality loss. The image is a turnkey GPU server - an OpenAI-compatible vLLM endpoint with int4_kivi enabled - launched via the included CloudFormation template. Supported models: head_dim 128 with standard attention (Qwen2.5 and Llama-3 families); the backend fails fast at startup rather than serve incorrect output for an unsupported model. Priced on density and quality, not latency: at long context on datacenter GPUs the backend trades some decode latency for density. Runs on g5, g6, g6e, p4d, and p5 GPU instances.
Highlights
- About 3x KV-cache density vs fp16 (int4 KIVI: per-channel-asymmetric KEY + per-token VALUE) - more concurrent users and longer context per GPU.
- Bit-identical to fp16 (greedy match 1.0000, verified on Qwen2.5 and Llama-3 families) - density with no measured quality loss.
- Turnkey GPU AMI: an OpenAI-compatible vLLM server with int4_kivi enabled out of the box; launch via the included CloudFormation.
Details
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Pricing
Dimension | Cost/hour |
|---|---|
g6.xlarge Recommended | $0.113 |
g5.2xlarge | $0.17 |
g6.2xlarge | $0.137 |
p5.48xlarge | $7.706 |
p4d.24xlarge | $3.074 |
g6e.12xlarge | $1.469 |
g6e.2xlarge | $0.314 |
g6e.xlarge | $0.261 |
g5.12xlarge | $0.794 |
g5.xlarge | $0.141 |
Vendor refund policy
Software fees are billed by AWS Marketplace on your consolidated AWS bill. Refund requests are handled per the AWS Marketplace refund policy; for product-specific questions email aws-support@abyo.net .
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Delivery details
64-bit (x86) Amazon Machine Image (AMI)
Amazon Machine Image (AMI)
An AMI is a virtual image that provides the information required to launch an instance. Amazon EC2 (Elastic Compute Cloud) instances are virtual servers on which you can run your applications and workloads, offering varying combinations of CPU, memory, storage, and networking resources. You can launch as many instances from as many different AMIs as you need.
Version release notes
Initial release.
Additional details
Usage instructions
Launch via the included CloudFormation template (deploy/cfn-gpu-serving.yaml): it creates the security group + IAM role and starts the vLLM OpenAI server with int4_kivi enabled. Set ModelId to a head_dim-128 model (e.g. Qwen/Qwen2.5-7B-Instruct). The OpenAI-compatible API is on port 8000 at /v1; health at /health.
Support
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Email support: aws-support@abyo.net
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AWS Support is a one-on-one, fast-response support channel that is staffed 24x7x365 with experienced and technical support engineers. The service helps customers of all sizes and technical abilities to successfully utilize the products and features provided by Amazon Web Services.
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