diff --git a/backend/cmd/regen/commands/root.go b/backend/cmd/regen/commands/root.go
index 4307bf7..97e3a52 100644
--- a/backend/cmd/regen/commands/root.go
+++ b/backend/cmd/regen/commands/root.go
@@ -1,6 +1,19 @@
 package commands
 
-import "github.com/spf13/cobra"
+import (
+	"github.com/FluidifyAI/Regen/backend/enterprise"
+	"github.com/spf13/cobra"
+)
+
+// proHooks holds the enterprise extension points used by the serve command.
+// Defaults to no-op stubs; regen-pro overrides via SetEnterpriseHooks.
+var proHooks = enterprise.NewNoOp()
+
+// SetEnterpriseHooks replaces the default no-op hooks with Pro implementations.
+// Must be called before Execute().
+func SetEnterpriseHooks(h enterprise.Hooks) {
+	proHooks = h
+}
 
 // NewRootCmd returns the cobra root command. All subcommands are attached here.
 func NewRootCmd() *cobra.Command {
diff --git a/backend/cmd/regen/commands/serve.go b/backend/cmd/regen/commands/serve.go
index a58064b..f4bc537 100644
--- a/backend/cmd/regen/commands/serve.go
+++ b/backend/cmd/regen/commands/serve.go
@@ -16,7 +16,6 @@ import (
 	"github.com/FluidifyAI/Regen/backend/internal/coordinator"
 	"github.com/FluidifyAI/Regen/backend/internal/coordinator/agents"
 	"github.com/FluidifyAI/Regen/backend/internal/database"
-	"github.com/FluidifyAI/Regen/backend/internal/enterprise"
 	"github.com/FluidifyAI/Regen/backend/internal/licence"
 	"github.com/FluidifyAI/Regen/backend/internal/metrics"
 	"github.com/FluidifyAI/Regen/backend/internal/redis"
@@ -177,9 +176,8 @@ func runServe(_ *cobra.Command, _ []string) error {
 	}
 
 	// Enterprise hooks — no-op stubs in the OSS build.
-	// Replace enterprise.NewNoOp() with the real implementation in the
-	// enterprise binary to unlock SCIM, audit log export, RBAC, and retention.
-	enterpriseHooks := enterprise.NewNoOp()
+	// regen-pro sets these via SetEnterpriseHooks() before calling Execute().
+	enterpriseHooks := proHooks
 
 	// Create the telemetry worker before SetupRoutes so we can inject its
 	// announcement getter as a closure — no import cycle with internal/worker.
diff --git a/backend/internal/enterprise/enterprise.go b/backend/enterprise/enterprise.go
similarity index 71%
rename from backend/internal/enterprise/enterprise.go
rename to backend/enterprise/enterprise.go
index 7fecd01..de97807 100644
--- a/backend/internal/enterprise/enterprise.go
+++ b/backend/enterprise/enterprise.go
@@ -4,7 +4,7 @@
 //
 // Enterprise repo usage:
 //
-//	import "github.com/FluidifyAI/Regen/backend/internal/enterprise"
+//	import "github.com/FluidifyAI/Regen/backend/enterprise"
 //
 //	hooks := enterprise.Hooks{
 //	    RBAC:      myrbac.NewProvider(db),
@@ -17,9 +17,11 @@ package enterprise
 
 import (
 	"context"
+	"io/fs"
 	"net/http"
 	"time"
 
+	"github.com/FluidifyAI/Regen/backend/ui"
 	"github.com/gin-gonic/gin"
 	"gorm.io/gorm"
 )
@@ -82,24 +84,47 @@ type RetentionEnforcer interface {
 	Start(ctx context.Context, db *gorm.DB)
 }
 
+// ── UI ────────────────────────────────────────────────────────────────────────
+
+// UIProvider supplies the embedded frontend filesystem served by the API server.
+// The OSS no-op returns the OSS build; the Pro binary returns a Pro-built FS
+// that includes all Pro-only pages and components.
+type UIProvider interface {
+	// FS returns the embedded frontend as an fs.FS rooted at dist/, or nil when
+	// no frontend has been built (the API still works, just no SPA).
+	FS() fs.FS
+}
+
+// ── Custom Fields ─────────────────────────────────────────────────────────────
+
+// CustomFieldsHandler mounts custom field definition endpoints.
+// The no-op stub returns 402 on all routes — custom fields require a Pro licence.
+type CustomFieldsHandler interface {
+	RegisterRoutes(group *gin.RouterGroup, db *gorm.DB)
+}
+
 // ── Hooks — the single struct threaded through the app ───────────────────────
 
 // Hooks is passed from serve.go to routes.go and worker.StartAll.
 // All fields default to their no-op stubs via NewNoOp().
 type Hooks struct {
-	RBAC      RBACProvider
-	Audit     AuditExporter
-	SCIM      SCIMHandler
-	Retention RetentionEnforcer
+	RBAC         RBACProvider
+	Audit        AuditExporter
+	SCIM         SCIMHandler
+	Retention    RetentionEnforcer
+	CustomFields CustomFieldsHandler
+	UI           UIProvider
 }
 
 // NewNoOp returns Hooks with all no-op stubs — the default for the OSS build.
 func NewNoOp() Hooks {
 	return Hooks{
-		RBAC:      noopRBAC{},
-		Audit:     noopAudit{},
-		SCIM:      noopSCIM{},
-		Retention: noopRetention{},
+		RBAC:         noopRBAC{},
+		Audit:        noopAudit{},
+		SCIM:         noopSCIM{},
+		Retention:    noopRetention{},
+		CustomFields: noopCustomFields{},
+		UI:           noopUI{},
 	}
 }
 
@@ -132,3 +157,20 @@ func (noopSCIM) RegisterRoutes(group *gin.RouterGroup) {
 type noopRetention struct{}
 
 func (noopRetention) Start(_ context.Context, _ *gorm.DB) {}
+
+// noopUI serves the OSS-built frontend. When no frontend has been compiled,
+// FS() returns nil and the router silently skips static file serving.
+type noopUI struct{}
+
+func (noopUI) FS() fs.FS { return ui.FS() }
+
+// noopCustomFields returns 402 on all routes — custom fields are a Pro feature.
+type noopCustomFields struct{}
+
+func (noopCustomFields) RegisterRoutes(group *gin.RouterGroup, _ *gorm.DB) {
+	group.Any("/*path", func(c *gin.Context) {
+		c.JSON(http.StatusPaymentRequired, gin.H{
+			"error": "custom fields require a Fluidify Regen Pro licence",
+		})
+	})
+}
diff --git a/backend/internal/api/middleware/audit.go b/backend/internal/api/middleware/audit.go
index d2e1d4d..0f4e1b5 100644
--- a/backend/internal/api/middleware/audit.go
+++ b/backend/internal/api/middleware/audit.go
@@ -3,7 +3,7 @@ package middleware
 import (
 	"time"
 
-	"github.com/FluidifyAI/Regen/backend/internal/enterprise"
+	"github.com/FluidifyAI/Regen/backend/enterprise"
 	"github.com/gin-gonic/gin"
 )
 
diff --git a/backend/internal/api/routes.go b/backend/internal/api/routes.go
index 931ae4e..06a30a4 100644
--- a/backend/internal/api/routes.go
+++ b/backend/internal/api/routes.go
@@ -12,12 +12,11 @@ import (
 	"github.com/FluidifyAI/Regen/backend/internal/api/handlers"
 	"github.com/FluidifyAI/Regen/backend/internal/api/middleware"
 	"github.com/FluidifyAI/Regen/backend/internal/config"
-	"github.com/FluidifyAI/Regen/backend/internal/enterprise"
+	"github.com/FluidifyAI/Regen/backend/enterprise"
 	"github.com/FluidifyAI/Regen/backend/internal/metrics"
 	"github.com/FluidifyAI/Regen/backend/internal/models/webhooks"
 	"github.com/FluidifyAI/Regen/backend/internal/repository"
 	"github.com/FluidifyAI/Regen/backend/internal/services"
-	"github.com/FluidifyAI/Regen/backend/ui"
 	"github.com/crewjam/saml/samlsp"
 	"github.com/gin-gonic/gin"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
@@ -437,6 +436,10 @@ func SetupRoutes(router *gin.Engine, db *gorm.DB, cfg *config.Config, teamsSvc *
 			settingsGroup.PATCH("/system/telemetry", handlers.PatchTelemetrySettings(systemSettingsRepo))
 		}
 
+		// Custom fields — Pro tier; no-op returns 402 in OSS build.
+		cfGroup := protected.Group("/custom-fields", middleware.RequireAdmin())
+		hooks.CustomFields.RegisterRoutes(cfGroup, db)
+
 		// Migrations — admin only (OPE-67)
 		migrationsGroup := protected.Group("/migrations", middleware.RequireAdmin())
 		{
@@ -456,7 +459,7 @@ func SetupRoutes(router *gin.Engine, db *gorm.DB, cfg *config.Config, teamsSvc *
 	// ui.Files() returns nil when the frontend has not been built (e.g. local
 	// development using `npm run dev`), in which case we skip static serving
 	// so the API remains fully functional on its own.
-	if distFS := ui.FS(); distFS != nil {
+	if distFS := hooks.UI.FS(); distFS != nil {
 		slog.Info("serving embedded frontend")
 
 		// Read index.html once at startup. All SPA routes serve this same file;
diff --git a/backend/internal/worker/start.go b/backend/internal/worker/start.go
index 6a7ef70..ea20bcb 100644
--- a/backend/internal/worker/start.go
+++ b/backend/internal/worker/start.go
@@ -5,7 +5,7 @@ import (
 	"log/slog"
 
 	"github.com/FluidifyAI/Regen/backend/internal/config"
-	"github.com/FluidifyAI/Regen/backend/internal/enterprise"
+	"github.com/FluidifyAI/Regen/backend/enterprise"
 	"github.com/FluidifyAI/Regen/backend/internal/repository"
 	"github.com/FluidifyAI/Regen/backend/internal/services"
 	"gorm.io/gorm"