@@ -50,7 +50,9 @@ def fixed(*spaces: dict) -> dict:
     f"{SINGLE}/plain.yaml": single_node_fragment(4),
     f"{MULTI}/disagg.yaml": {
         "base": {"schema": 2, "engine": "sglang", "roles": {
-            "prefill": {"nodes": 1, "args": {"mem-fraction-static": 0.8}}, "decode": {"nodes": 1},
+            "prefill": {"nodes": 1, "args": {"mem-fraction-static": 0.8},
+                        "env": {"UCX_NET_DEVICES": "@fabric.ucx-net-devices"}},
+            "decode": {"nodes": 1},
         }},
         "override_a": {"roles": {"decode": {"args": {"max-running-requests": 64}}}},
         "override_b": {"roles": {"decode": {"args": {"max-running-requests": 128}}}},
@@ -67,7 +69,7 @@ def fixed(*spaces: dict) -> dict:
     "gpus-per-node": 8, "available-cpu-dram-mib": 1024000, "arch": "x86_64", "scheduler": "slurm",
     "slurm": {"partition": "batch", "exclusive": True, "srt-slurm": {
         "network-interface": "eth0", "mounts": {"/data/models": "/models"},
-        "power-exporter-port": 9400,
+        "power-exporter-port": 9400, "fabric": {"ucx-net-devices": ["mlx5_0:1"]},
     }},
 }}}  # fmt: skip
 
@@ -170,12 +172,13 @@ def edit(project: Path, path: str, change) -> None:
         ),
         set(), id="agentx-eval-variant",
     ),
-    # Cluster facts: model mounts and the DCGM exporter port.
+    # Cluster facts: model mounts, the DCGM exporter port and the fabric behind references.
     pytest.param(
         "configs/runners.yaml",
-        lambda runners: runners["clusters"]["fixture"]["slurm"]["srt-slurm"].update(
-            {"mounts": {"/scratch/models": "/models"}, "power-exporter-port": 9500}
-        ),
+        lambda runners: runners["clusters"]["fixture"]["slurm"]["srt-slurm"].update({
+            "mounts": {"/scratch/models": "/models"}, "power-exporter-port": 9500,
+            "fabric": {"ucx-net-devices": ["mlx5_1:1", "mlx5_2:1"]},
+        }),
         set(), id="cluster-facts",
     ),
 ])  # fmt: skip