diff --git a/engine_test.go b/engine_test.go
index 2a9beb8..19e1cb9 100644
--- a/engine_test.go
+++ b/engine_test.go
@@ -1154,6 +1154,73 @@ func TestOpenAICompatibleProfileRunsThroughNormalProfilePath(t *testing.T) {
 	}
 }
 
+func TestOpenAICompatibleProfileDefersExtraParamsValidation(t *testing.T) {
+	cyclic := map[string]any{}
+	cyclic["self"] = cyclic
+
+	prof := scriptorium.OpenAICompatibleProfile(scriptorium.OpenAICompatibleProfileConfig{
+		ID:          "cyclic-template-profile",
+		Endpoint:    "http://cyclic-template/v1",
+		Model:       "cyclic-template-model",
+		ExtraParams: cyclic,
+	})
+
+	_, err := scriptorium.NewEngine(scriptorium.Config{PromptDir: "./examples/prompts"},
+		scriptorium.WithProfiles(prof),
+	)
+	if !errors.Is(err, scriptorium.ErrInvalidConfig) {
+		t.Fatalf("expected ErrInvalidConfig, got %v", err)
+	}
+}
+
+func TestOpenAICompatibleProfileNestedExtraParamsRunThroughWithProfiles(t *testing.T) {
+	fake := &fakeLLMClient{response: &scriptorium.GenerateResponse{Content: "ok"}}
+	nested := map[string]any{
+		"labels": map[string]string{"route": "primary"},
+		"ids":    []int{1, 2, 3},
+	}
+	extraParams := map[string]any{
+		"nested": nested,
+	}
+	prof := scriptorium.OpenAICompatibleProfile(scriptorium.OpenAICompatibleProfileConfig{
+		ID:          "nested-template-profile",
+		Endpoint:    "http://nested-template/v1",
+		Model:       "nested-template-model",
+		ExtraParams: extraParams,
+	})
+	extraParams["added"] = "mutated-after-construction"
+
+	engine, err := scriptorium.NewEngine(scriptorium.Config{
+		PromptDir: "./examples/prompts",
+		SchemaDir: "./examples/schemas",
+	}, scriptorium.WithProfiles(prof), scriptorium.WithLLMClient(fake))
+	if err != nil {
+		t.Fatalf("expected engine construction to succeed, got %v", err)
+	}
+	nested["added"] = "mutated-after-construction"
+
+	_, err = engine.Run(context.Background(), scriptorium.RunRequest{
+		PromptID:  "generic.markdown_summary",
+		ProfileID: "nested-template-profile",
+		Inputs: map[string]scriptorium.ArtifactRef{
+			"transcript": scriptorium.Inline("Rin opens the gate."),
+			"glossary":   scriptorium.Inline("gate: A guarded passage."),
+		},
+	})
+	if err != nil {
+		t.Fatalf("expected run to succeed, got %v", err)
+	}
+	want := map[string]any{
+		"nested": map[string]any{
+			"labels": map[string]string{"route": "primary"},
+			"ids":    []int{1, 2, 3},
+		},
+	}
+	if !reflect.DeepEqual(fake.requests[0].Target.ExtraParams, want) {
+		t.Fatalf("unexpected extra params:\ngot=%#v\nwant=%#v", fake.requests[0].Target.ExtraParams, want)
+	}
+}
+
 func TestInMemoryProfileAPIKeyRequiredBehavior(t *testing.T) {
 	engine, err := scriptorium.NewEngine(scriptorium.Config{
 		PromptDir: "./examples/prompts",
diff --git a/profiles.go b/profiles.go
index 8f60c43..334638e 100644
--- a/profiles.go
+++ b/profiles.go
@@ -28,10 +28,21 @@ func OpenAICompatibleProfile(cfg OpenAICompatibleProfileConfig) Profile {
 		ServiceTier:     cfg.ServiceTier,
 		ReasoningEffort: cfg.ReasoningEffort,
 		APIKeyRequired:  cfg.APIKeyRequired,
-		ExtraParams:     copyAnyMap(cfg.ExtraParams),
+		ExtraParams:     copyShallowAnyMap(cfg.ExtraParams),
 	}
 }
 
+func copyShallowAnyMap(src map[string]any) map[string]any {
+	if src == nil {
+		return nil
+	}
+	out := make(map[string]any, len(src))
+	for k, v := range src {
+		out[k] = v
+	}
+	return out
+}
+
 type memoryProfileRepository struct {
 	profiles map[string]domain.ExecutionProfile
 }