A served model can be moved to more cards, or fewer

llmgw ctl model gpus MODEL N [--profile P] [--in-place],
POST /api/v1/models/{name}/gpus and the console's GPUs…: how many cards of
one node each replica uses. Tensor parallel for vLLM, SGLang and
TensorRT-LLM, held to the model's KV heads (modelplan.SplitsHeads, now one
rule for the planner and this); the layers split for llama.cpp, its old
--tensor-split dropped. Refused for a count no node has, for cards that
would not hold the weights and the context, and for engines on one card.
The replicas start again beside the old ones; with no room beside them the
command says so, and --in-place stops each first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/control/adminapi/api.go

@@ -206,6 +206,7 @@ func (a *API) Register(mux Mux) {
 	mux.HandleFunc("POST /api/v1/updates/check", a.checkUpdates)
 	mux.HandleFunc("POST /api/v1/models/{name}/update", a.updateModel)
 	mux.HandleFunc("POST /api/v1/models/{name}/context", a.setModelContext)
+	mux.HandleFunc("POST /api/v1/models/{name}/gpus", a.setModelGPUs)
 	mux.HandleFunc("POST /api/v1/models/{name}/rollback", a.rollbackModel)
 	a.registerCanary(mux)
 	a.registerEval(mux)
@@ -1774,6 +1775,26 @@ func (a *API) setModelContext(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, change)
 }
 
+// setModelGPUs spreads a served model over more cards, or fewer, and
+// starts its replicas again on it.
+func (a *API) setModelGPUs(w http.ResponseWriter, r *http.Request) {
+	if a.serve == nil {
+		writeError(w, http.StatusNotImplemented, "this control plane cannot change a model's cards")
+		return
+	}
+	var req modelserve.GPUsRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	change, err := a.serve.SetGPUs(r.Context(), r.PathValue("name"), req, actorOf(r))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	writeJSON(w, http.StatusOK, change)
+}
+
 func (a *API) listUpdates(w http.ResponseWriter, _ *http.Request) {
 	out := make([]modelserve.UpdateInfo, 0)
 	if a.serve != nil {

internal/control/adminapi/routes.go

@@ -215,6 +215,9 @@ var Routes = []Route{
 		Request:     modelserve.Change{}, OptionalBody: true, Response: modelserve.Job{}, Status: http.StatusAccepted},
 	{Method: "POST", Path: "/api/v1/models/{name}/context", Summary: "Change a served model's context: the catalog, its engines' arguments and memory, then its replicas restarted",
 		Request: modelserve.ContextRequest{}, Response: modelserve.ContextChange{}},
+	{Method: "POST", Path: "/api/v1/models/{name}/gpus", Summary: "Spread a served model over more cards or fewer: its profile, checked against its KV heads, its cards' memory and the nodes, then its replicas restarted",
+		Description: "Tensor parallel for vLLM, SGLang and TensorRT-LLM, a layer split for llama.cpp, on one node. With no room beside the running replicas, in_place stops each first.",
+		Request:     modelserve.GPUsRequest{}, Response: modelserve.GPUsChange{}},
 	{Method: "POST", Path: "/api/v1/models/{name}/rollback", Summary: "Go back to the weights the last update replaced",
 		Response: Result{}},
 	{Method: "POST", Path: "/api/v1/models/{name}/origin", Summary: "Record the repository a model's weights came from",