diff --git a/persistent-memory.d/2026-09-01-pfi-gx10-onboarding.md b/persistent-memory.d/2026-09-01-pfi-gx10-onboarding.md
index de98742..8cbf13c 100644
--- a/persistent-memory.d/2026-09-01-pfi-gx10-onboarding.md
+++ b/persistent-memory.d/2026-09-01-pfi-gx10-onboarding.md
@@ -253,3 +253,62 @@ Still outstanding, all needing root:
     - racking (playbooks/gx10-rack-network.yaml) -- optional, NOT a prerequisite
 
 **Nothing above blocks the run-3c throughput probe**, which needs only the driver and torch.
+
+## `[2026-09-01 23:5x]` Run-3c throughput probe — IN FLIGHT, and the ana-ml2 baseline is now on record
+
+### The baseline nobody had written down: ana-ml2's real s/it for run 3c
+
+Extracted from `/tank/erp-tune/run-03c.log` (the actual run, before the breaker killed it):
+
+    step 10   10.81 s/it       step 20   12.88 s/it       step 24   15.76 s/it
+    => 604 steps on ana-ml2 ~= 2.2-2.7 h
+
+**This is the number the GX10 has to be compared against**, and it was sitting in a log
+nobody had reduced. Anything under ~45 s/it on the GX10 makes 604 steps an overnight run.
+
+### Exact run-3c geometry (from run-03c.json + a real adapter_config.json)
+
+    base            /tank/aimodels/gemma4-26b-a4b-it-bf16   49 GB
+                    gemma4, 30 layers, hidden 2816, 16 heads / 8 KV, MoE (A4B),
+                    vocab 262144, sliding_window 1024, multimodal (vision+audio configs)
+    LoRA            r 64, alpha 128, dropout 0.0, bias none, 205 target modules
+                    (q/k/v/o + gate/up/down across all 30 language-model layers)
+    shape           max_seq_len 16384, per_device_batch 2, grad_accum 8 (effective 16)
+    other           gradient_checkpointing true, bf16, cosine, warmup 0.1, wd 0.01
+    length          604 optimizer steps, 1 epoch, save_steps 50
+
+### ⚠ THE BACKEND-DELTA TRAP — CHECKED, and it is NOT present
+
+CLAUDE.md warns that two frontier-panel conclusions were voided because a benchmark and a
+trainer had silently different attention backends. Enumerated both sides **before** running:
+
+    ana-ml2   flash_attn NOT installed in /tank/erp-tune/venv  -> falls back to sdpa
+    pfi-gx10  flash_attn not available for aarch64/sm_121      -> falls back to sdpa
+
+Same backend both sides. ⚠ **Library versions DO differ and it is recorded rather than
+assumed harmless:**
+
+    ana-ml2   torch 2.13.0        transformers 5.15.1   peft 0.20.0   accelerate 1.14.0
+    pfi-gx10  torch 2.14.0+cu130  transformers 5.16.1   peft 0.20.0   accelerate 1.14.0
+
+The probe reads the **resolved** `_attn_implementation` back off the loaded model rather than
+trusting the request, so the comparison is checkable rather than assumed.
+
+### Probe design (§4-disciplined)
+
+`~/ml/probe_3c.py` on the GX10. Real geometry, synthetic batches — it measures step cost, and
+padding on the real run is 0.0% so the corpus does not change per-step cost materially.
+
+- **12 steps, first 2 discarded as warmup.** Non-negotiable here: an unwarmed benchmark on
+  this box already read 27 TFLOP/s when the true figure was 93, because it was timing the PTX
+  JIT. sm_121 is not in torch's arch list.
+- Reports the **step-time distribution** (median, min/max, every step), not a mean beside a
+  settings dump.
+- Emits **every provenance key always, null when unused** — present-and-null, not absent.
+
+### Transfer
+
+49 GB relayed **ana-ml2 -> nh3-dev -> pfi-gx10**, ~33 MB/s, ~25 min. Relayed rather than
+direct because ana-ml2's key is not authorised for `infra-ops@pfi-gx10` — and relaying costs
+nothing extra, since the Wi-Fi leg is the bottleneck either way. **Deliberately did not add an
+access grant just to save a hop.**