diff --git a/admin-compliance/app/sdk/iace/[projectId]/_components/VariantPanel.tsx b/admin-compliance/app/sdk/iace/[projectId]/_components/VariantPanel.tsx
new file mode 100644
index 0000000..6db00e1
--- /dev/null
+++ b/admin-compliance/app/sdk/iace/[projectId]/_components/VariantPanel.tsx
@@ -0,0 +1,253 @@
+'use client'
+
+import { useState, useEffect, useCallback } from 'react'
+import Link from 'next/link'
+
+interface VariantProject {
+  id: string
+  machine_name: string
+  description?: string
+  status: string
+  hazard_count?: number
+  parent_project_id?: string
+}
+
+interface VariantGapResponse {
+  base_project: { id: string; name: string; hazard_count: number; measure_count: number }
+  variant: { id: string; name: string; hazard_count: number; measure_count: number }
+  gap: { additional_hazards: number; additional_measures: number; categories_affected: string[] }
+}
+
+interface Props {
+  projectId: string
+  parentProjectId?: string | null
+  parentProjectName?: string
+}
+
+export function VariantPanel({ projectId, parentProjectId, parentProjectName }: Props) {
+  const [variants, setVariants] = useState<VariantProject[]>([])
+  const [gapMap, setGapMap] = useState<Record<string, VariantGapResponse>>({})
+  const [loading, setLoading] = useState(true)
+  const [showCreate, setShowCreate] = useState(false)
+  const [creating, setCreating] = useState(false)
+  const [name, setName] = useState('')
+  const [description, setDescription] = useState('')
+
+  const fetchVariants = useCallback(async () => {
+    try {
+      const res = await fetch(`/api/sdk/v1/iace/projects/${projectId}/variants`)
+      if (!res.ok) {
+        setVariants([])
+        return
+      }
+      const json = await res.json()
+      const list: VariantProject[] = json.variants || json.projects || []
+      setVariants(list)
+
+      // Fetch gap analysis for this project
+      const gapRes = await fetch(`/api/sdk/v1/iace/projects/${projectId}/variant-gap`)
+      if (gapRes.ok) {
+        const gapJson = await gapRes.json()
+        const gaps: Record<string, VariantGapResponse> = {}
+        // Could be a single gap or array — handle both
+        if (Array.isArray(gapJson)) {
+          for (const g of gapJson) {
+            gaps[g.variant?.id] = g
+          }
+        } else if (gapJson.variant) {
+          gaps[gapJson.variant.id] = gapJson
+        }
+        setGapMap(gaps)
+      }
+    } catch {
+      setVariants([])
+    } finally {
+      setLoading(false)
+    }
+  }, [projectId])
+
+  useEffect(() => {
+    fetchVariants()
+  }, [fetchVariants])
+
+  async function handleCreate() {
+    if (!name.trim()) return
+    setCreating(true)
+    try {
+      const res = await fetch(`/api/sdk/v1/iace/projects/${projectId}/variants`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          machine_name: name.trim(),
+          description: description.trim(),
+        }),
+      })
+      if (res.ok) {
+        setName('')
+        setDescription('')
+        setShowCreate(false)
+        fetchVariants()
+      }
+    } catch {
+      // silently handle
+    } finally {
+      setCreating(false)
+    }
+  }
+
+  // If this project IS a variant, show link to base project
+  if (parentProjectId) {
+    return (
+      <div className="bg-white dark:bg-gray-800 rounded-xl border border-purple-200 dark:border-purple-700 p-6">
+        <div className="flex items-center gap-3">
+          <div className="w-10 h-10 bg-purple-50 dark:bg-purple-900/30 rounded-lg flex items-center justify-center">
+            <svg className="w-5 h-5 text-purple-600" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+              <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M7 16V4m0 0L3 8m4-4l4 4m6 0v12m0 0l4-4m-4 4l-4-4" />
+            </svg>
+          </div>
+          <div className="flex-1">
+            <p className="text-sm font-semibold text-gray-900 dark:text-white">Variante</p>
+            <p className="text-xs text-gray-500">
+              Dieses Projekt ist eine Variante des Basis-Projekts
+            </p>
+          </div>
+          <Link
+            href={`/sdk/iace/${parentProjectId}`}
+            className="inline-flex items-center gap-1.5 px-3 py-1.5 text-sm font-medium text-purple-700 bg-purple-50 rounded-lg hover:bg-purple-100 dark:text-purple-300 dark:bg-purple-900/30 dark:hover:bg-purple-900/50 transition-colors"
+          >
+            {parentProjectName || 'Basis-Projekt'}
+            <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+              <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M13 7l5 5m0 0l-5 5m5-5H6" />
+            </svg>
+          </Link>
+        </div>
+      </div>
+    )
+  }
+
+  if (loading) return null
+  if (variants.length === 0 && !showCreate) {
+    return (
+      <div className="bg-white dark:bg-gray-800 rounded-xl border border-gray-200 dark:border-gray-700 p-6">
+        <div className="flex items-center justify-between">
+          <div className="flex items-center gap-3">
+            <div className="w-10 h-10 bg-gray-50 dark:bg-gray-700 rounded-lg flex items-center justify-center">
+              <svg className="w-5 h-5 text-gray-400" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M8 16H6a2 2 0 01-2-2V6a2 2 0 012-2h8a2 2 0 012 2v2m-6 12h8a2 2 0 002-2v-8a2 2 0 00-2-2h-8a2 2 0 00-2 2v8a2 2 0 002 2z" />
+              </svg>
+            </div>
+            <div>
+              <p className="text-sm font-semibold text-gray-900 dark:text-white">Keine Varianten</p>
+              <p className="text-xs text-gray-500">Erstellen Sie Varianten fuer verschiedene Betriebsarten</p>
+            </div>
+          </div>
+          <button
+            onClick={() => setShowCreate(true)}
+            className="px-3 py-1.5 text-sm font-medium text-purple-700 bg-purple-50 rounded-lg hover:bg-purple-100 dark:text-purple-300 dark:bg-purple-900/30 dark:hover:bg-purple-900/50 transition-colors"
+          >
+            + Neue Variante
+          </button>
+        </div>
+        {renderCreateDialog()}
+      </div>
+    )
+  }
+
+  function renderCreateDialog() {
+    if (!showCreate) return null
+    return (
+      <div className="mt-4 p-4 border border-purple-200 dark:border-purple-700 rounded-lg bg-purple-50/50 dark:bg-purple-900/10 space-y-3">
+        <h3 className="text-sm font-semibold text-gray-900 dark:text-white">Neue Variante erstellen</h3>
+        <input
+          type="text"
+          placeholder="Variantenname (z.B. Kollaborierender Betrieb)"
+          value={name}
+          onChange={(e) => setName(e.target.value)}
+          className="w-full px-3 py-2 text-sm border border-gray-300 rounded-lg bg-white dark:bg-gray-800 dark:border-gray-600 dark:text-white focus:ring-2 focus:ring-purple-500 focus:border-transparent"
+        />
+        <textarea
+          placeholder="Beschreibung (optional)"
+          value={description}
+          onChange={(e) => setDescription(e.target.value)}
+          rows={2}
+          className="w-full px-3 py-2 text-sm border border-gray-300 rounded-lg bg-white dark:bg-gray-800 dark:border-gray-600 dark:text-white focus:ring-2 focus:ring-purple-500 focus:border-transparent"
+        />
+        <div className="flex gap-2 justify-end">
+          <button
+            onClick={() => { setShowCreate(false); setName(''); setDescription('') }}
+            className="px-3 py-1.5 text-sm text-gray-600 hover:text-gray-800 dark:text-gray-400"
+          >
+            Abbrechen
+          </button>
+          <button
+            onClick={handleCreate}
+            disabled={creating || !name.trim()}
+            className="px-4 py-1.5 text-sm font-medium text-white bg-purple-600 rounded-lg hover:bg-purple-700 disabled:opacity-50 transition-colors"
+          >
+            {creating ? 'Erstelle...' : 'Erstellen'}
+          </button>
+        </div>
+      </div>
+    )
+  }
+
+  return (
+    <div className="bg-white dark:bg-gray-800 rounded-xl border border-gray-200 dark:border-gray-700 p-6 space-y-4">
+      <div className="flex items-center justify-between">
+        <div className="flex items-center gap-3">
+          <div className="w-10 h-10 bg-purple-50 dark:bg-purple-900/30 rounded-lg flex items-center justify-center">
+            <svg className="w-5 h-5 text-purple-600" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+              <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M8 16H6a2 2 0 01-2-2V6a2 2 0 012-2h8a2 2 0 012 2v2m-6 12h8a2 2 0 002-2v-8a2 2 0 00-2-2h-8a2 2 0 00-2 2v8a2 2 0 002 2z" />
+            </svg>
+          </div>
+          <div>
+            <h2 className="text-sm font-semibold text-gray-900 dark:text-white">
+              Varianten ({variants.length})
+            </h2>
+            <p className="text-xs text-gray-500">Betriebsart-spezifische Projektversionen</p>
+          </div>
+        </div>
+        <button
+          onClick={() => setShowCreate(true)}
+          className="px-3 py-1.5 text-sm font-medium text-purple-700 bg-purple-50 rounded-lg hover:bg-purple-100 dark:text-purple-300 dark:bg-purple-900/30 dark:hover:bg-purple-900/50 transition-colors"
+        >
+          + Neue Variante
+        </button>
+      </div>
+
+      <div className="grid grid-cols-1 sm:grid-cols-2 gap-3">
+        {variants.map((v) => {
+          const gap = gapMap[v.id]
+          return (
+            <Link
+              key={v.id}
+              href={`/sdk/iace/${v.id}`}
+              className="block p-4 border border-gray-200 dark:border-gray-700 rounded-lg hover:shadow-md hover:border-purple-300 transition-all group"
+            >
+              <div className="flex items-start justify-between gap-2">
+                <div className="min-w-0 flex-1">
+                  <p className="text-sm font-medium text-gray-900 dark:text-white truncate group-hover:text-purple-700 dark:group-hover:text-purple-400">
+                    {v.machine_name}
+                  </p>
+                  {v.description && (
+                    <p className="text-xs text-gray-500 mt-0.5 line-clamp-2">{v.description}</p>
+                  )}
+                </div>
+                <svg className="w-4 h-4 text-gray-400 group-hover:text-purple-600 flex-shrink-0 mt-0.5" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+                  <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M13 7l5 5m0 0l-5 5m5-5H6" />
+                </svg>
+              </div>
+              {gap && gap.gap.additional_hazards > 0 && (
+                <span className="inline-flex items-center mt-2 px-2 py-0.5 text-xs font-medium bg-orange-100 text-orange-800 dark:bg-orange-900/50 dark:text-orange-300 rounded-full">
+                  +{gap.gap.additional_hazards} Gefaehrdungen
+                </span>
+              )}
+            </Link>
+          )
+        })}
+      </div>
+
+      {renderCreateDialog()}
+    </div>
+  )
+}
diff --git a/admin-compliance/app/sdk/iace/[projectId]/page.tsx b/admin-compliance/app/sdk/iace/[projectId]/page.tsx
index 1cdc51f..ad83eae 100644
--- a/admin-compliance/app/sdk/iace/[projectId]/page.tsx
+++ b/admin-compliance/app/sdk/iace/[projectId]/page.tsx
@@ -5,6 +5,7 @@ import Link from 'next/link'
 import { useParams } from 'next/navigation'
 import { SuggestedNorms } from './_components/SuggestedNorms'
 import { ComplianceAlerts } from './_components/ComplianceAlerts'
+import { VariantPanel } from './_components/VariantPanel'
 
 interface ProjectOverview {
   id: string
@@ -15,6 +16,8 @@ interface ProjectOverview {
   completeness_pct: number
   created_at: string
   updated_at: string
+  parent_project_id?: string | null
+  parent_project_name?: string
   metadata?: { limits_form?: Record<string, unknown> }
   risk_summary?: {
     critical?: number
@@ -125,12 +128,26 @@ export default function ProjectOverviewPage() {
       const stepsComplete = [hasLimits, hasComponents, hasHazards, hasMitigations].filter(Boolean).length
       const completeness = Math.round((stepsComplete / 6) * 100)
 
+      // If this is a variant, resolve parent project name
+      let parentName: string | undefined
+      if (json.parent_project_id) {
+        try {
+          const parentRes = await fetch(`/api/sdk/v1/iace/projects/${json.parent_project_id}`)
+          if (parentRes.ok) {
+            const parentJson = await parentRes.json()
+            parentName = parentJson.machine_name
+          }
+        } catch { /* ignore */ }
+      }
+
       setProject({
         ...json,
         completeness_pct: completeness,
         component_count: compCount,
         hazard_count: hazCount,
         mitigation_count: mitCount,
+        parent_project_id: json.parent_project_id || null,
+        parent_project_name: parentName,
         metadata: json.metadata,
         risk_summary: {
           critical: rs.critical || 0,
@@ -334,6 +351,13 @@ export default function ProjectOverviewPage() {
       {/* Compliance Alerts */}
       <ComplianceAlerts projectId={projectId} />
 
+      {/* Variant Management */}
+      <VariantPanel
+        projectId={projectId}
+        parentProjectId={project.parent_project_id}
+        parentProjectName={project.parent_project_name}
+      />
+
       {/* Suggested Norms */}
       <SuggestedNorms projectId={projectId} />
 
diff --git a/admin-compliance/app/sdk/iace/layout.tsx b/admin-compliance/app/sdk/iace/layout.tsx
index 0adc87a..c53ff8e 100644
--- a/admin-compliance/app/sdk/iace/layout.tsx
+++ b/admin-compliance/app/sdk/iace/layout.tsx
@@ -108,12 +108,40 @@ export default function IACELayout({ children }: { children: React.ReactNode })
   const params = useParams()
   const projectId = params?.projectId as string | undefined
   const [projectName, setProjectName] = React.useState('')
+  const [variantInfo, setVariantInfo] = React.useState<{
+    parentProjectId?: string; parentName?: string; variantCount?: number
+  }>({})
 
   React.useEffect(() => {
     if (!projectId) return
     fetch(`/api/sdk/v1/iace/projects/${projectId}`)
       .then(r => r.ok ? r.json() : null)
-      .then(d => { if (d?.machine_name) setProjectName(d.machine_name) })
+      .then(async (d) => {
+        if (!d?.machine_name) return
+        setProjectName(d.machine_name)
+        // Resolve variant info
+        if (d.parent_project_id) {
+          try {
+            const pRes = await fetch(`/api/sdk/v1/iace/projects/${d.parent_project_id}`)
+            if (pRes.ok) {
+              const pj = await pRes.json()
+              setVariantInfo({ parentProjectId: d.parent_project_id, parentName: pj.machine_name })
+            } else {
+              setVariantInfo({ parentProjectId: d.parent_project_id })
+            }
+          } catch { setVariantInfo({ parentProjectId: d.parent_project_id }) }
+        } else {
+          // Check if this project has variants
+          try {
+            const vRes = await fetch(`/api/sdk/v1/iace/projects/${projectId}/variants`)
+            if (vRes.ok) {
+              const vj = await vRes.json()
+              const list = vj.variants || vj.projects || []
+              if (list.length > 0) setVariantInfo({ variantCount: list.length })
+            }
+          } catch { /* no variants endpoint yet */ }
+        }
+      })
       .catch(() => {})
   }, [projectId])
 
@@ -148,6 +176,21 @@ export default function IACELayout({ children }: { children: React.ReactNode })
                 {projectName}
               </p>
             )}
+            {variantInfo.parentProjectId && (
+              <Link
+                href={`/sdk/iace/${variantInfo.parentProjectId}`}
+                className="mt-1 flex items-center gap-1 text-[10px] text-orange-600 hover:text-orange-700 dark:text-orange-400 truncate"
+                title={variantInfo.parentName ? `Variante von: ${variantInfo.parentName}` : 'Variante'}
+              >
+                <svg className="w-3 h-3 flex-shrink-0" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+                  <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M7 16V4m0 0L3 8m4-4l4 4" />
+                </svg>
+                Variante von: {variantInfo.parentName || 'Basis'}
+              </Link>
+            )}
+            {variantInfo.variantCount != null && variantInfo.variantCount > 0 && (
+              <p className="mt-1 text-[10px] text-gray-400">({variantInfo.variantCount} Varianten)</p>
+            )}
             <p className="text-[10px] text-gray-400 mt-0.5">CE-Compliance</p>
             <Link
               href="/sdk/iace/lines"
diff --git a/ai-compliance-sdk/internal/api/handlers/iace_handler_projects.go b/ai-compliance-sdk/internal/api/handlers/iace_handler_projects.go
index 6858e90..cffd95a 100644
--- a/ai-compliance-sdk/internal/api/handlers/iace_handler_projects.go
+++ b/ai-compliance-sdk/internal/api/handlers/iace_handler_projects.go
@@ -308,3 +308,88 @@ func (h *IACEHandler) InitFromProfile(c *gin.Context) {
 		"regulations_triggered": triggeredRegulations,
 	})
 }
+
+// ============================================================================
+// Variant Management
+// ============================================================================
+
+// CreateVariant handles POST /projects/:id/variants
+// Creates a new variant sub-project linked to the given base project.
+func (h *IACEHandler) CreateVariant(c *gin.Context) {
+	parentID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid project ID"})
+		return
+	}
+
+	// Verify parent project exists
+	parent, err := h.store.GetProject(c.Request.Context(), parentID)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	if parent == nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "parent project not found"})
+		return
+	}
+
+	var req iace.CreateProjectRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	// Force the parent link
+	req.ParentProjectID = &parentID
+
+	project, err := h.store.CreateProject(c.Request.Context(), parent.TenantID, req)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusCreated, gin.H{"project": project})
+}
+
+// ListVariants handles GET /projects/:id/variants
+// Returns all variant sub-projects for a given base project.
+func (h *IACEHandler) ListVariants(c *gin.Context) {
+	parentID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid project ID"})
+		return
+	}
+
+	variants, err := h.store.ListVariants(c.Request.Context(), parentID)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	if variants == nil {
+		variants = []iace.Project{}
+	}
+
+	c.JSON(http.StatusOK, iace.ProjectListResponse{
+		Projects: variants,
+		Total:    len(variants),
+	})
+}
+
+// GetVariantGap handles GET /projects/:id/variant-gap
+// Returns a gap analysis comparing a variant against its base project.
+func (h *IACEHandler) GetVariantGap(c *gin.Context) {
+	variantID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid project ID"})
+		return
+	}
+
+	gap, err := h.store.GetVariantGap(c.Request.Context(), variantID)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gap)
+}
diff --git a/ai-compliance-sdk/internal/app/routes.go b/ai-compliance-sdk/internal/app/routes.go
index 52fa4c2..683b9f3 100644
--- a/ai-compliance-sdk/internal/app/routes.go
+++ b/ai-compliance-sdk/internal/app/routes.go
@@ -371,6 +371,9 @@ func registerIACERoutes(v1 *gin.RouterGroup, h *handlers.IACEHandler) {
 		iaceRoutes.PUT("/projects/:id", h.UpdateProject)
 		iaceRoutes.DELETE("/projects/:id", h.ArchiveProject)
 		iaceRoutes.POST("/projects/:id/init-from-profile", h.InitFromProfile)
+		iaceRoutes.POST("/projects/:id/variants", h.CreateVariant)
+		iaceRoutes.GET("/projects/:id/variants", h.ListVariants)
+		iaceRoutes.GET("/projects/:id/variant-gap", h.GetVariantGap)
 		iaceRoutes.POST("/projects/:id/completeness-check", h.CheckCompleteness)
 		iaceRoutes.POST("/projects/:id/components", h.CreateComponent)
 		iaceRoutes.GET("/projects/:id/components", h.ListComponents)
diff --git a/ai-compliance-sdk/internal/iace/models_api.go b/ai-compliance-sdk/internal/iace/models_api.go
index de731c6..d08c040 100644
--- a/ai-compliance-sdk/internal/iace/models_api.go
+++ b/ai-compliance-sdk/internal/iace/models_api.go
@@ -12,6 +12,7 @@ import (
 
 // CreateProjectRequest is the API request for creating a new IACE project
 type CreateProjectRequest struct {
+	ParentProjectID *uuid.UUID      `json:"parent_project_id,omitempty"`
 	MachineName     string          `json:"machine_name" binding:"required"`
 	MachineType     string          `json:"machine_type" binding:"required"`
 	Manufacturer    string          `json:"manufacturer" binding:"required"`
@@ -199,6 +200,28 @@ type ValidateMitigationHierarchyResponse struct {
 	Warnings []string `json:"warnings,omitempty"`
 }
 
+// VariantGap compares a variant project against its base project
+type VariantGap struct {
+	BaseProject ProjectSummary `json:"base_project"`
+	Variant     ProjectSummary `json:"variant"`
+	Gap         GapDetail      `json:"gap"`
+}
+
+// ProjectSummary is a lightweight project view for gap comparisons
+type ProjectSummary struct {
+	ID           uuid.UUID `json:"id"`
+	Name         string    `json:"name"`
+	HazardCount  int       `json:"hazard_count"`
+	MeasureCount int       `json:"measure_count"`
+}
+
+// GapDetail describes the delta between variant and base project
+type GapDetail struct {
+	AdditionalHazards  int      `json:"additional_hazards"`
+	AdditionalMeasures int      `json:"additional_measures"`
+	CategoriesAffected []string `json:"categories_affected"`
+}
+
 // CompletenessGate represents a single gate in the project completeness checklist
 type CompletenessGate struct {
 	ID       string `json:"id"`
diff --git a/ai-compliance-sdk/internal/iace/models_entities.go b/ai-compliance-sdk/internal/iace/models_entities.go
index 9a0a318..0c304a7 100644
--- a/ai-compliance-sdk/internal/iace/models_entities.go
+++ b/ai-compliance-sdk/internal/iace/models_entities.go
@@ -15,6 +15,7 @@ import (
 type Project struct {
 	ID                   uuid.UUID       `json:"id"`
 	TenantID             uuid.UUID       `json:"tenant_id"`
+	ParentProjectID      *uuid.UUID      `json:"parent_project_id,omitempty"`
 	MachineName          string          `json:"machine_name"`
 	MachineType          string          `json:"machine_type"`
 	Manufacturer         string          `json:"manufacturer"`
diff --git a/ai-compliance-sdk/internal/iace/store_projects.go b/ai-compliance-sdk/internal/iace/store_projects.go
index a2d0712..c8de01f 100644
--- a/ai-compliance-sdk/internal/iace/store_projects.go
+++ b/ai-compliance-sdk/internal/iace/store_projects.go
@@ -19,6 +19,7 @@ func (s *Store) CreateProject(ctx context.Context, tenantID uuid.UUID, req Creat
 	project := &Project{
 		ID:              uuid.New(),
 		TenantID:        tenantID,
+		ParentProjectID: req.ParentProjectID,
 		MachineName:     req.MachineName,
 		MachineType:     req.MachineType,
 		Manufacturer:    req.Manufacturer,
@@ -33,18 +34,19 @@ func (s *Store) CreateProject(ctx context.Context, tenantID uuid.UUID, req Creat
 
 	_, err := s.pool.Exec(ctx, `
 		INSERT INTO iace_projects (
-			id, tenant_id, machine_name, machine_type, manufacturer,
+			id, tenant_id, parent_project_id, machine_name, machine_type, manufacturer,
 			description, narrative_text, status, ce_marking_target,
 			completeness_score, risk_summary, triggered_regulations, metadata,
 			created_at, updated_at, archived_at
 		) VALUES (
-			$1, $2, $3, $4, $5,
-			$6, $7, $8, $9,
-			$10, $11, $12, $13,
-			$14, $15, $16
+			$1, $2, $3, $4, $5, $6,
+			$7, $8, $9, $10,
+			$11, $12, $13, $14,
+			$15, $16, $17
 		)
 	`,
-		project.ID, project.TenantID, project.MachineName, project.MachineType, project.Manufacturer,
+		project.ID, project.TenantID, project.ParentProjectID,
+		project.MachineName, project.MachineType, project.Manufacturer,
 		project.Description, project.NarrativeText, string(project.Status), project.CEMarkingTarget,
 		project.CompletenessScore, nil, project.TriggeredRegulations, project.Metadata,
 		project.CreatedAt, project.UpdatedAt, project.ArchivedAt,
@@ -64,13 +66,13 @@ func (s *Store) GetProject(ctx context.Context, id uuid.UUID) (*Project, error)
 
 	err := s.pool.QueryRow(ctx, `
 		SELECT
-			id, tenant_id, machine_name, machine_type, manufacturer,
+			id, tenant_id, parent_project_id, machine_name, machine_type, manufacturer,
 			description, narrative_text, status, ce_marking_target,
 			completeness_score, risk_summary, triggered_regulations, metadata,
 			created_at, updated_at, archived_at
 		FROM iace_projects WHERE id = $1
 	`, id).Scan(
-		&p.ID, &p.TenantID, &p.MachineName, &p.MachineType, &p.Manufacturer,
+		&p.ID, &p.TenantID, &p.ParentProjectID, &p.MachineName, &p.MachineType, &p.Manufacturer,
 		&p.Description, &p.NarrativeText, &status, &p.CEMarkingTarget,
 		&p.CompletenessScore, &riskSummary, &triggeredRegulations, &metadata,
 		&p.CreatedAt, &p.UpdatedAt, &p.ArchivedAt,
@@ -94,7 +96,7 @@ func (s *Store) GetProject(ctx context.Context, id uuid.UUID) (*Project, error)
 func (s *Store) ListProjects(ctx context.Context, tenantID uuid.UUID) ([]Project, error) {
 	rows, err := s.pool.Query(ctx, `
 		SELECT
-			id, tenant_id, machine_name, machine_type, manufacturer,
+			id, tenant_id, parent_project_id, machine_name, machine_type, manufacturer,
 			description, narrative_text, status, ce_marking_target,
 			completeness_score, risk_summary, triggered_regulations, metadata,
 			created_at, updated_at, archived_at
@@ -113,7 +115,7 @@ func (s *Store) ListProjects(ctx context.Context, tenantID uuid.UUID) ([]Project
 		var riskSummary, triggeredRegulations, metadata []byte
 
 		err := rows.Scan(
-			&p.ID, &p.TenantID, &p.MachineName, &p.MachineType, &p.Manufacturer,
+			&p.ID, &p.TenantID, &p.ParentProjectID, &p.MachineName, &p.MachineType, &p.Manufacturer,
 			&p.Description, &p.NarrativeText, &status, &p.CEMarkingTarget,
 			&p.CompletenessScore, &riskSummary, &triggeredRegulations, &metadata,
 			&p.CreatedAt, &p.UpdatedAt, &p.ArchivedAt,
@@ -231,3 +233,150 @@ func (s *Store) UpdateProjectCompleteness(ctx context.Context, id uuid.UUID, sco
 	return nil
 }
 
+// ListVariants returns all variant sub-projects for a given parent project
+func (s *Store) ListVariants(ctx context.Context, parentID uuid.UUID) ([]Project, error) {
+	rows, err := s.pool.Query(ctx, `
+		SELECT
+			id, tenant_id, parent_project_id, machine_name, machine_type, manufacturer,
+			description, narrative_text, status, ce_marking_target,
+			completeness_score, risk_summary, triggered_regulations, metadata,
+			created_at, updated_at, archived_at
+		FROM iace_projects WHERE parent_project_id = $1
+		ORDER BY created_at DESC
+	`, parentID)
+	if err != nil {
+		return nil, fmt.Errorf("list variants: %w", err)
+	}
+	defer rows.Close()
+
+	var variants []Project
+	for rows.Next() {
+		var p Project
+		var status string
+		var riskSummary, triggeredRegulations, metadata []byte
+
+		err := rows.Scan(
+			&p.ID, &p.TenantID, &p.ParentProjectID, &p.MachineName, &p.MachineType, &p.Manufacturer,
+			&p.Description, &p.NarrativeText, &status, &p.CEMarkingTarget,
+			&p.CompletenessScore, &riskSummary, &triggeredRegulations, &metadata,
+			&p.CreatedAt, &p.UpdatedAt, &p.ArchivedAt,
+		)
+		if err != nil {
+			return nil, fmt.Errorf("list variants scan: %w", err)
+		}
+
+		p.Status = ProjectStatus(status)
+		json.Unmarshal(riskSummary, &p.RiskSummary)
+		json.Unmarshal(triggeredRegulations, &p.TriggeredRegulations)
+		json.Unmarshal(metadata, &p.Metadata)
+
+		variants = append(variants, p)
+	}
+
+	return variants, nil
+}
+
+// GetVariantGap computes the gap analysis between a variant and its base project.
+// It counts hazards and measures in each, and returns the categories affected.
+func (s *Store) GetVariantGap(ctx context.Context, variantID uuid.UUID) (*VariantGap, error) {
+	variant, err := s.GetProject(ctx, variantID)
+	if err != nil {
+		return nil, fmt.Errorf("get variant: %w", err)
+	}
+	if variant == nil {
+		return nil, fmt.Errorf("variant project not found")
+	}
+	if variant.ParentProjectID == nil {
+		return nil, fmt.Errorf("project is not a variant (no parent_project_id)")
+	}
+
+	parent, err := s.GetProject(ctx, *variant.ParentProjectID)
+	if err != nil {
+		return nil, fmt.Errorf("get parent: %w", err)
+	}
+	if parent == nil {
+		return nil, fmt.Errorf("parent project not found")
+	}
+
+	// Count hazards and measures for both projects
+	parentHazards, parentMeasures, err := s.countHazardsAndMeasures(ctx, parent.ID)
+	if err != nil {
+		return nil, fmt.Errorf("count parent stats: %w", err)
+	}
+	variantHazards, variantMeasures, err := s.countHazardsAndMeasures(ctx, variant.ID)
+	if err != nil {
+		return nil, fmt.Errorf("count variant stats: %w", err)
+	}
+
+	// Get unique hazard categories in the variant
+	categories, err := s.getVariantHazardCategories(ctx, variant.ID)
+	if err != nil {
+		return nil, fmt.Errorf("get variant categories: %w", err)
+	}
+
+	return &VariantGap{
+		BaseProject: ProjectSummary{
+			ID:           parent.ID,
+			Name:         parent.MachineName,
+			HazardCount:  parentHazards,
+			MeasureCount: parentMeasures,
+		},
+		Variant: ProjectSummary{
+			ID:           variant.ID,
+			Name:         variant.MachineName,
+			HazardCount:  variantHazards,
+			MeasureCount: variantMeasures,
+		},
+		Gap: GapDetail{
+			AdditionalHazards:  variantHazards,
+			AdditionalMeasures: variantMeasures,
+			CategoriesAffected: categories,
+		},
+	}, nil
+}
+
+// countHazardsAndMeasures returns (hazardCount, measureCount) for a project
+func (s *Store) countHazardsAndMeasures(ctx context.Context, projectID uuid.UUID) (int, int, error) {
+	var hazardCount int
+	err := s.pool.QueryRow(ctx,
+		`SELECT COUNT(*) FROM iace_hazards WHERE project_id = $1`, projectID,
+	).Scan(&hazardCount)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	var measureCount int
+	err = s.pool.QueryRow(ctx, `
+		SELECT COUNT(*) FROM iace_mitigations m
+		JOIN iace_hazards h ON m.hazard_id = h.id
+		WHERE h.project_id = $1
+	`, projectID).Scan(&measureCount)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	return hazardCount, measureCount, nil
+}
+
+// getVariantHazardCategories returns distinct hazard categories for a project
+func (s *Store) getVariantHazardCategories(ctx context.Context, projectID uuid.UUID) ([]string, error) {
+	rows, err := s.pool.Query(ctx,
+		`SELECT DISTINCT category FROM iace_hazards WHERE project_id = $1 ORDER BY category`,
+		projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var categories []string
+	for rows.Next() {
+		var cat string
+		if err := rows.Scan(&cat); err != nil {
+			return nil, err
+		}
+		categories = append(categories, cat)
+	}
+	return categories, nil
+}
+