# gemma-4-E4B against gemma-4-12B on the routing fixture

*Measured 2026-08-09 on workpc. The owner asked for the swap. This is what it costs.*

Both arms ran the same 96-case fixture through `TestLLMRouterBaseline`, minutes
apart, against the same llama-server build and the same mavgpud. The 12B arm is a
control run and not the 2026-08-02 number. That one predates five fixture cases,
the destination labels and a llama.cpp upgrade.

| | full | intent-only | destination | p50 | p95 |
|---|---|---|---|---|---|
| gemma-4-12B-it-qat-UD-Q4_K_XL, MTP draft | 81/96 (84.4%) | 91.7% | 23/33 (69.7%) | 344ms | 471ms |
| gemma-4-E4B-it-qat-UD-Q4_K_XL | 80/96 (83.3%) | 89.6% | 19/33 (57.6%) | 294ms | 562ms |

E4B costs one case of full accuracy, two of intent and **four of destination**,
and buys 50ms at p50. Read the destination column as the finding. One case is
three points on 33. So 23 against 19 is outside the noise a single case makes,
and the other two columns are not.

Both arms produce three false clarifies and one missed clarify, and neither
errored on any case.

## What E4B loses

Four of the five destination regressions are the same shape: it names nothing
where the 12B names `recall` or `calendar`. `ru-query-015` ("сколько я прошёл
шагов") goes further and names `self`. Naming nothing is the safe direction,
because `SourceUnknown` walks the whole chain, so these turns are still answered.
They cost latency and they are what a fourth head is meant to fix (V-546).

Two Russian intent cases regress, both with the interrogative off the front.
`ru-chat-003` ("расскажи анекдот про программистов") goes to `query`.
`ru-fact-003` ("поужинал") goes to `chat`.

## MTP

E4B has none, and there is no way to give it any on this box. MTP on workpc is
a separate gguf of architecture `gemma4-assistant` carrying
`nextn_predict_layers=4`, and `mtp-gemma-4-12B-it-BF16.gguf` is the only one on
disk. Its head is trained against the 12B's hidden states, so it cannot drive an
E4B target. Scanning both target ggufs finds no `nextn` tensors in either, so
neither model self-speculates.

So the 12B arm above ran with speculative decoding and E4B ran without, and E4B
was still faster.

## Cost on the card

E4B is 4.2GB against 6.7GB plus a 0.86GB draft. With CW2 resident at 1.6GB that
is 5.8GB of 16GB against 9.2GB. Nothing in Maven needs the difference, so this is
headroom for the owner's own jobs rather than a capability.
