Inferact details vLLM optimizations for AgentX agentic coding benchmark

Congratulations to @SemiAnalysis_ on the release of AgentX 1.0 🎊, an open-source multi-turn agentic coding benchmark collected from ~$3M of real traces, running on 1000+ chips and ~2MW of continuously operated compute. We are excited to see @vllm_project’s competitive performance on frontier open models: 🔷130,093 tok/s/chip for DeepSeek V4 Pro 🔷 77,079 tok/s/chip for Minimax M3 🔷 12,479 tok/s/chip for Kimi K3. The following thread covers an overview of the work from @vllm_project and @inferact: what we tested, found, and shipped upstream. This work highlights vLLM’s performance on real-world workloads and our committed focus to making vLLM an agentic-first engine. Optimizing AgentX performance meant tackling three major challenges: prefix reuse, efficient long context parallelism, and scaling performance with PD disaggregation. First, long agentic sessions stress prefix caching and KV cache offloading. Modern hybrid models have greatly reduced the required KV cache sizes, and caching every block boundary still saturates the KV cache pool which causes prefix cache thrashing across sessions. The fix was sparse retention: one state per interval-sized segment plus the latest replay boundary (vllm-project/vllm #43447, #45845), then preserving shared-prefix boundaries so the interval can go to 0 for agent sessions (#47782). That gets us >95% hit rate at 14 concurrent requests with contexts to 1M. The bigger structural change in KV cache offloading was making the shared KV pool distributed. With Mooncake Store as a first-class connector, prefill ranks can hit the prefix cache both within a worker and across workers, so we no longer have to trade cache locality against load balance to keep a cluster busy. Session-aware routing (48048) is what lets the router act on it. For a single node deployment, SimpleCPUOffloadConnector has been greatly improved to support all hybrid model architectures and across both CUDA and ROCm platforms. For DeepSeek V4 Pro on ROCm, this implementation gave +81.7% output throughput and 46.6% lower mean e2e latency versus recomputing the prefix. Kimi K3 at 2.8T barely fits on a single node, and squeezing it in leaves almost no headroom for KV cache, which is exactly what a long multi-turn session needs most. Parallelism strategy matters more here than on any other model we tested. TP8/DCP8 tops the K3 agentic frontier across configs, with B300 vLLM peaking at ~12.5k tok/s/chip at ~8 tok/s/user and GB300 NVL72 on Dynamo + vLLM holding the curve out past 200 tok/s/user. K3 also surfaced a routing bug worth pulling: vllm-project/router#194 fixes the router dropping reasoning_content, which hits any reasoning model served behind it. On MiniMax M3, B200 vLLM reaches ~44k tok/s/chip and vLLM leads TRT-LLM on throughput vs p90 TTFT. M3 and Qwen3.5 both shipped day-0. Finally, fully optimized performance requires scaling the deployment with prefill-decode disaggregation and distributed KV cache offloading. Thanks to vLLM’s MultiConnector, this is natively supported with NIXL PD connector + MooncakeStoreConnector. By rate matching to find the ideal prefill-decode ratio, we achieved 4.45x higher throughput at a 60 tok/s interactivity for DeepSeek V4 Pro on GB300 Dynamo compared to B300. Shoutout to @NVIDIAAI, who co-tuned most of these configs with us. Dynamo's router optimizations took AgentX replay time down 23.7% on the vLLM backend, the AIPerf replay harness is what made the traces runnable at all, and NIXL and their kernels sit under each respective performance point. Shoutout to @AIatAMD as well: the team’s AITER sparse-MLA decode selection led to +5.22% AgentX output throughput; the hybrid AITER/native CSA selector led to 1.21–1.76x e2e performance boost, and the team made prebuilt lmcache gfx942/gfx950 wheels and a published Mooncake ROCm wheel. Thank you to @SemiAnalysis_ for building AgentX and for the collaboration throughout. Agentic workloads are what users serve in real production, and benchmarking on real workloads is what improves vLLM and open source inference. Next up: more upstream work and a blog with a full technical deep dive later this week. Stay tuned. 🚀