Leadership1 publisher3 min readPublished
Nvidia's agent-workload lead scales with interactivity, and the second-source budget line does not
SemiAnalysis's AgentX replays recorded coding-agent sessions instead of fixed prompts. On that traffic, the reported Nvidia-AMD cost gap grows as the interactivity target rises.
The Board Room · Leadership desk
What happened
- SemiAnalysis released AgentX on August 24, an open source benchmark that replays recorded coding-agent sessions against production inference stacks instead of fixed-length prompts.
- On GLM 5.3 through open source SGLang, it reports Nvidia hardware up to five times better on cost efficiency than AMD at 150 output tokens per second per user.
- The replayed traffic has a median input of 142,000 tokens against a median output of 444, with 3.84 seconds of idle time between turns while the agent waits on a tool.
- The corpus came from a proxy on SemiAnalysis staff using Claude Code and Codex: more than 8,000 sessions and 610 billion tokens.
- AMD's ATOM engine beats a GB300 NVL72 rack running vLLM on price-performance across part of the Kimi K3 curve between 40 and 60 seconds of latency.
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Why it matters
- exposure SemiAnalysis puts the floor below free: at that operating point, accelerators donated at zero cost would still lose on cost per token once hosting and power are paid, which leaves whoever signed...
- constraint With AMD backends absent from vLLM's supported context-parallel paths, the parallelism strategy long contexts depend on most is the one a second source cannot currently lean on upstream.
- contradiction AMD's clearest price-performance win runs on an engine SemiAnalysis says is barely in production outside one Alibaba advertising unit, so the ordering flips depending on which serving stack a...
- decision If agentic sessions really are the bulk of production inference, capacity plans signed off on fixed-prompt throughput need re-running against trace replay before the next tranche is committed.
The mechanism worth arguing about is where reusable state sits between turns. On DeepSeek V4, SemiAnalysis measured a 91% cache hit rate in high-bandwidth memory on a B300 configuration with 3 terabytes of DRAM and eight-way expert parallel decode at 384 concurrent sessions, with another 1.36% served from host memory [13]. The same engine on B200, at concurrency 196, hit 73% in HBM and pulled a further 20% off the host [14]. Total coverage is almost the same, roughly 92.4% against 93% [6]. What differs is which tier answers, and SemiAnalysis ties the heavier offload to sharply worse latency as user counts scale [14]. That is why the reported gap is not a constant: on the same model, B200's advantage over MI355X sits near 57% at 108 output tokens per second per user and 247% at 141 [4]. Thirty-three tokens per second of extra responsiveness multiplies the advantage by more than four [3].
Two other things only appear when a benchmark has a previous turn. Median input of 142,000 tokens against median output of 444 works out to roughly 320 tokens in for every token out [1], and 45% of the public sessions spawn at least one subagent [4]. Nvidia's TensorRT-LLM added boundary-aware incremental tokenization so a conversation resending its history does not re-tokenize it; on a Qwen 3.5 trace it matched full tokenization across all 1,087 transitions while mean per-turn processing time fell from 185.1 milliseconds to 11.3 [15], a cut of about 94% [2]. A fixed 8,000-in, 1,000-out sequence has no prior turn to reuse and therefore cannot show any of it [12].
The procurement question this reframes is not which vendor is faster in the abstract. It is what interactivity number goes into the service level target, because that number now selects the answer. Lowering it does not flip the ordering in the published data, only narrows it [4]. And the ledger against AMD gets worse on like-for-like open stacks: Qwen 3.5 served through SGLang on both sides puts Nvidia more than 20 times ahead at 90 tokens per second per user, according to SemiAnalysis [19].
Two caveats belong in the same breath. Forbes reads the five-times figure as a claim about one configuration rather than a market-wide ratio [5], and the public v1.0 subset is 393 Claude Code sessions under Apache 2.0 [8], transformed into session-scoped chained hash blocks of 64 tokens each so that prefix relationships survive but the original prompts and code do not [9]. That preserves the cache behaviour the argument rests on. It also means the evidence describes coding agents, replayed from one firm's own developers, and anyone buying on it is extrapolating from that to their own traffic.
What to watch
- Whether ATOM picks up production adoption beyond the single Alibaba unit, or whether AMD's wins stay confined to a stack customers do not run.
- Whether AMD publishes its own trace-replay numbers on upstream open stacks, and at which interactivity points it chooses to publish them.
- Whether anyone replays AgentX against non-coding agent traffic and gets the same ordering.