# Frontier coverage audit for Qwen3.6-27B

> **Verdict (2026-07-17): `FAIL: original Frontier coverage`.** This is a
> static capability result, not a latency-fidelity result. It says that the
> examined existing Frontier cannot represent the real Qwen3.6 execution
> contract; it does not say that a future extended simulator will be wrong.

## Question

Before spending profile or replay GPU-hours, can the checked Frontier baseline
simulate the same model/engine state that the real server executes?

## Compared contracts

| Side | Observed contract |
|---|---|
| Real server | ModelScope `Qwen/Qwen3.6-27B@cea40373b9214dd387123e68841890af30dcd469`; vLLM 0.20.2, BF16; `Qwen3_5ForConditionalGeneration`; 64-layer non-MoE hybrid with three Gated DeltaNet/linear-state layers followed by one gated-attention layer per block. The release vLLM run used a FlashInfer GDN prefill kernel and changed requested `--block-size 16` to a 784-token attention/state page at TP1/2/4. |
| Frontier baseline | `/home/admin/cpfs/wjh/frontier-qwen30-vllm020-profile-v1/Frontier`, commit `d9cfeb6d8791fbf2f295dd9744c56a666171776e`. Its model-spec directory has Qwen2/Qwen3-MoE and all-attention dense examples, but no Qwen3.6 or Qwen3_5 spec. Source search across `*.py`, `*.json`, `*.md` returned no hit for `qwen3_5`, `qwen3.6`, `GatedDeltaNet`, `DeltaNet`, `mamba`, `linear attention`, `state cache`, or `gdn`. |

## Frontier source model-spec inventory

This is the complete `frontend/configs/model_configs/*.json` inventory at the
checked commit. It establishes that the simulator can instantiate these
*structural specifications*; it is **not** evidence that a matching vLLM
profile, runtime contract, or validated tuning result exists for each model.

| Class | Source specs |
|---|---|
| All-attention, non-MoE | `Llama-3.1-405B-Instruct-FP8`, `Llama-3.2-1B-Instruct`, `llama2_7b_dense_example`, `llama3.1-405b`, `llama3.1-8b`, `llama3.3-70b`, `qwen2_dense_test` |
| MoE | `Phi-tiny-MoE-instruct`, `Qwen3-235B-A22B`, `Qwen3-235B-A22B__layers96`, `Qwen3-30B-A3B-tiny`, `deepseek-v3`, `mixtral_8x7b_moe`, `qwen2_moe_example`, `qwen3-a3b-30b-moe`, `qwen3-next-80b-a3b-instruct-reduced-l2`, `qwen3-next-80b-a3b-instruct-reduced-l20`, `Step2Mini-tiny`, `step-moe-noquant-small`, `step-moe-noquant`, `step-moe` |

The exact JSON architecture labels are `llama`, `qwen2`, `phimoe`,
`qwen3_moe`, `deepseek_v3`, `mixtral`, `qwen2_moe`, `qwen3_next`,
`step2_mini`, and `step3_text`.  The separately held experimental artifacts
in this project establish profile-and-surface evidence only for
`Qwen3-30B-A3B` and `Qwen3-235B-A22B`; the remaining names are not
automatically runnable or validated on H20/vLLM merely because a JSON exists.

## Why the missing model file is semantic, not administrative

The Frontier execution-time taxonomy separates `attention_prefill_execution_time`
and `attention_decode_execution_time`; its operator context and parameter
accounting are built from attention Q/KV heads, attention head dimension, FFN,
and optional MoE routing. No Gated-DeltaNet/linear-state operator, state-cache
capacity rule, or its mixed prefill/decode scheduling state was found.

Adding a JSON whose layer count merely matches Qwen3.6 would therefore map
three quarters of its text layers onto an all-attention approximation. Reusing
Qwen30/MoE or Qwen3.5 profiles has the same defect. Neither is a valid
execution of the existing baseline.

## Decision

1. Record Frontier as **coverage failure** for the Qwen3.6 non-MoE-hybrid
   branch. Do not rank configs, fabricate high latency, or spend GPU-hours on
   an all-attention profile substitute.
2. A new Gated-DeltaNet/state-cache model and profiling implementation would
   be an **extended Frontier** intervention. It must be evaluated separately
   from the capability of the original simulator and cannot support the claim
   that existing Frontier already solves tuning.
3. The Qwen3.6 result cannot be presented as evidence for a conventional pure
   dense-transformer class. It is a useful non-MoE/hybrid boundary case.
4. No runnable local checkout/version of Vidur or APEX was found; only a
   historical Vidur patch exists. Their coverage remains **unassessed**, not
   passed or failed, until their exact released artifacts are frozen and
   checked against this model/runtime contract.

## Next critical experiment

Do not extend Frontier before establishing the requested no-SLO metric on a
model it already represents. The next direct test is the existing
Qwen3-30B-A3B MoE branch under one same-trace Fixed-P replay surface, scored
by mean/p90 TTFT and E2E (TPOT `N/A`), with simulator-only coverage checked
before any real 600-s sweep. This separates a known architectural coverage
failure from a fidelity failure on an in-scope model.

## Evidence locations

- Real topology smoke and resolved page state:
  `artifacts/qwen36/smoke-v4-20260717/` in this run directory.
- Real model/runtime audit:
  [dense-preflight.md](dense-preflight.md).
- No-SLO latency protocol and selection gates:
  [experiment-card.md](experiment-card.md).