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Choose from two reproducible workload profiles, including operating effort and recovery. A single favourable request does not create a universal engine ranking.
Compare SGLang and vLLM using the same model and workload, rather than a universal ranking. First establish compatibility, then align artifacts, request formatting and cache conditions. A timing difference between unmatched configurations cannot be attributed solely to the serving engine.
Check minimum compatibility
Verify model architecture, weight format and hardware support for both installed releases. Start each engine through its documented workflow and obtain a valid control answer. If one cannot support a required feature, describe that specific limitation before discussing speed.
Record exact versions and launch arguments. A comparison becomes difficult to reproduce if one side uses a mutable container image while the other is pinned. Preserve the actual image or package identity and the checkpoint revision for both.
Compare operating controls
| Criterion | SGLang | vLLM |
|---|---|---|
| Basic launch | Its server command and arguments | serve and engine arguments |
| Static memory | mem-fraction-static budget | Instance memory and cache budget |
| Repeated prefixes | Supported caching for the chosen setup | Prefix caching for the chosen mode |
| Load acceptance | Matched external traffic and metrics | The same traffic or compatible test |
These differences identify what to record, not a numerical winner. Similar percentages or similarly named options do not necessarily allocate memory in the same way. Confirm the meaning of each control in the corresponding release.
Align inputs and cache state
Preserve messages, chat template, output limit and actual token counts. Check answer quality on a fixed example set before timing. Different stopping behaviour can make a faster-looking answer incomplete for the task.
Separate cold, warm and repeated-prefix runs. If one engine receives reusable prefixes and the other starts without that state, the result describes different operating conditions. Use the same concurrency and request schedule, and label each scenario clearly.
Measure queueing and recovery
After single requests work, use several increasing traffic levels. Record completed requests, first meaningful content, total latency, memory and errors. Queueing belongs to the user experience even if the engine’s active generation looks fast.
Also measure startup and the first request after restart. A repeatable recovery procedure and clear logs can matter to the team as much as one throughput number. Finish with a configuration card for each engine: artifact, version, settings, quality, memory, timing and manual work. That supports a workload-specific decision without inventing results for hardware or traffic you have not tested.
Turn the check into a practical next step
Choose from two reproducible workload profiles, including operating effort and recovery. A single favourable request does not create a universal engine ranking.
For the documented details, consult the primary documentation; configuration reference. Continue with sglang docker launch and vllm bench serve command.