diff --git a/web/backend/api/models.go b/web/backend/api/models.go
index 145d7ac4a..f1761cb70 100644
--- a/web/backend/api/models.go
+++ b/web/backend/api/models.go
@@ -743,23 +743,50 @@ func fetchOpenAICompatibleModels(ctx context.Context, fetchURL, apiKey string) (
 		return nil, fmt.Errorf("upstream returned status %d", resp.StatusCode)
 	}
 
-	var parsed struct {
-		Data []struct {
-			ID      string `json:"id"`
-			OwnedBy string `json:"owned_by"`
-		} `json:"data"`
-	}
-	if err := json.NewDecoder(resp.Body).Decode(&parsed); err != nil {
-		return nil, err
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("read response: %w", err)
 	}
 
-	models := make([]upstreamModel, 0, len(parsed.Data))
-	for _, m := range parsed.Data {
-		if m.ID != "" {
-			models = append(models, upstreamModel{ID: m.ID, OwnedBy: m.OwnedBy})
-		}
+	type modelItem struct {
+		ID      string `json:"id"`
+		OwnedBy string `json:"owned_by"`
 	}
-	return models, nil
+
+	// {"data": [...]} envelope. Distinguish "envelope shape with empty list"
+	// from "object without a data key" via Data being non-nil after unmarshal:
+	// json.Unmarshal sets Data to []modelItem{} for `{"data":[]}` but leaves
+	// it as nil when "data" is absent or null.
+	var envelope struct {
+		Data []modelItem `json:"data"`
+	}
+	if err := json.Unmarshal(body, &envelope); err == nil && envelope.Data != nil {
+		models := make([]upstreamModel, 0, len(envelope.Data))
+		for _, m := range envelope.Data {
+			if m.ID != "" {
+				models = append(models, upstreamModel{ID: m.ID, OwnedBy: m.OwnedBy})
+			}
+		}
+		return models, nil
+	}
+
+	// Bare-array shape, including `[]`.
+	var arr []modelItem
+	if err := json.Unmarshal(body, &arr); err == nil {
+		models := make([]upstreamModel, 0, len(arr))
+		for _, m := range arr {
+			if m.ID != "" {
+				models = append(models, upstreamModel{ID: m.ID, OwnedBy: m.OwnedBy})
+			}
+		}
+		return models, nil
+	}
+
+	preview := body
+	if len(preview) > 256 {
+		preview = preview[:256]
+	}
+	return nil, fmt.Errorf("decode response: unrecognized shape: %s", strings.TrimSpace(string(preview)))
 }
 
 func fetchOllamaModels(ctx context.Context, fetchURL string) ([]upstreamModel, error) {
diff --git a/web/backend/api/models_test.go b/web/backend/api/models_test.go
index 0b1f04848..71b6b279c 100644
--- a/web/backend/api/models_test.go
+++ b/web/backend/api/models_test.go
@@ -3,6 +3,7 @@ package api
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -2219,3 +2220,174 @@ func TestMaskAPIKey(t *testing.T) {
 		})
 	}
 }
+
+func TestFetchOpenAICompatibleModels_ResponseShapes(t *testing.T) {
+	tests := []struct {
+		name      string
+		response  string
+		apiKey    string
+		wantLen   int
+		wantFirst struct {
+			id, ownedBy string
+		}
+		wantSecond struct {
+			id, ownedBy string
+		}
+	}{
+		{
+			name:     "envelope shape",
+			response: `{"data":[{"id":"gpt-4o","owned_by":"openai"},{"id":"gpt-4o-mini","owned_by":"openai"}]}`,
+			apiKey:   "test-key",
+			wantLen:  2,
+			wantFirst: struct {
+				id, ownedBy string
+			}{id: "gpt-4o", ownedBy: "openai"},
+			wantSecond: struct {
+				id, ownedBy string
+			}{id: "gpt-4o-mini", ownedBy: "openai"},
+		},
+		{
+			name:     "bare array shape",
+			response: `[{"id":"qwen-max","owned_by":"qwen"},{"id":"qwen-plus","owned_by":"qwen"}]`,
+			apiKey:   "",
+			wantLen:  2,
+			wantFirst: struct {
+				id, ownedBy string
+			}{id: "qwen-max", ownedBy: "qwen"},
+			wantSecond: struct {
+				id, ownedBy string
+			}{id: "qwen-plus", ownedBy: "qwen"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.Header().Set("Content-Type", "application/json")
+				fmt.Fprint(w, tt.response)
+			}))
+			defer srv.Close()
+
+			models, err := fetchOpenAICompatibleModels(t.Context(), srv.URL+"/models", tt.apiKey)
+			if err != nil {
+				t.Fatalf("error = %v", err)
+			}
+			if len(models) != tt.wantLen {
+				t.Fatalf("len(models) = %d, want %d", len(models), tt.wantLen)
+			}
+			if models[0].ID != tt.wantFirst.id || models[0].OwnedBy != tt.wantFirst.ownedBy {
+				t.Fatalf("models[0] = %+v, want {ID:%s OwnedBy:%s}", models[0], tt.wantFirst.id, tt.wantFirst.ownedBy)
+			}
+			if models[1].ID != tt.wantSecond.id || models[1].OwnedBy != tt.wantSecond.ownedBy {
+				t.Fatalf("models[1] = %+v, want {ID:%s OwnedBy:%s}", models[1], tt.wantSecond.id, tt.wantSecond.ownedBy)
+			}
+		})
+	}
+}
+
+func TestFetchOpenAICompatibleModels_EmptyEnvelopeReturnsEmptySlice(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `{"data":[]}`)
+	}))
+	defer srv.Close()
+
+	models, err := fetchOpenAICompatibleModels(t.Context(), srv.URL+"/models", "k")
+	if err != nil {
+		t.Fatalf("error = %v", err)
+	}
+	if len(models) != 0 {
+		t.Fatalf("len(models) = %d, want 0", len(models))
+	}
+}
+
+func TestFetchOpenAICompatibleModels_EmptyBareArrayReturnsEmptySlice(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `[]`)
+	}))
+	defer srv.Close()
+
+	models, err := fetchOpenAICompatibleModels(t.Context(), srv.URL+"/models", "k")
+	if err != nil {
+		t.Fatalf("error = %v", err)
+	}
+	if len(models) != 0 {
+		t.Fatalf("len(models) = %d, want 0", len(models))
+	}
+}
+
+func TestFetchOpenAICompatibleModels_UnrecognizedShape(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `{"models":[],"error":"unsupported"}`)
+	}))
+	defer srv.Close()
+
+	_, err := fetchOpenAICompatibleModels(t.Context(), srv.URL+"/models", "k")
+	if err == nil {
+		t.Fatal("error = nil, want unrecognized shape error")
+	}
+	if !strings.Contains(err.Error(), "unrecognized shape") {
+		t.Fatalf("error = %q, want it to contain 'unrecognized shape'", err.Error())
+	}
+}
+
+func TestFetchOpenAICompatibleModels_FiltersEmptyIDs(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `{"data":[`+
+			`{"id":"gpt-4o","owned_by":"openai"},`+
+			`{"id":"","owned_by":"openai"},`+
+			`{"id":"gpt-4o-mini"}]}`)
+	}))
+	defer srv.Close()
+
+	models, err := fetchOpenAICompatibleModels(t.Context(), srv.URL+"/models", "k")
+	if err != nil {
+		t.Fatalf("error = %v", err)
+	}
+	if len(models) != 2 {
+		t.Fatalf("len(models) = %d, want 2 (empty IDs should be filtered)", len(models))
+	}
+	if models[0].ID != "gpt-4o" {
+		t.Fatalf("models[0].ID = %q, want %q", models[0].ID, "gpt-4o")
+	}
+	if models[1].ID != "gpt-4o-mini" {
+		t.Fatalf("models[1].ID = %q, want %q", models[1].ID, "gpt-4o-mini")
+	}
+}
+
+func TestFetchOpenAICompatibleModels_SetsAuthorizationHeader(t *testing.T) {
+	var gotAuth string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotAuth = r.Header.Get("Authorization")
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `{"data":[{"id":"m1"}]}`)
+	}))
+	defer srv.Close()
+
+	if _, err := fetchOpenAICompatibleModels(t.Context(), srv.URL+"/models", "my-secret-key"); err != nil {
+		t.Fatalf("error = %v", err)
+	}
+	if gotAuth != "Bearer my-secret-key" {
+		t.Fatalf("Authorization = %q, want %q", gotAuth, "Bearer my-secret-key")
+	}
+}
+
+func TestFetchOpenAICompatibleModels_NoAuthHeaderWhenKeyEmpty(t *testing.T) {
+	var gotAuth string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotAuth = r.Header.Get("Authorization")
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `[{"id":"m1"}]`)
+	}))
+	defer srv.Close()
+
+	if _, err := fetchOpenAICompatibleModels(t.Context(), srv.URL+"/models", ""); err != nil {
+		t.Fatalf("error = %v", err)
+	}
+	if gotAuth != "" {
+		t.Fatalf("Authorization = %q, want empty", gotAuth)
+	}
+}