diff --git a/lib/arcadia_cloud/catalog.ex b/lib/arcadia_cloud/catalog.ex
index f13244b..3718388 100644
--- a/lib/arcadia_cloud/catalog.ex
+++ b/lib/arcadia_cloud/catalog.ex
@@ -25,6 +25,22 @@ defmodule ArcadiaCloud.Catalog do
     Repo.get_by(Plan, code: code)
   end
 
+  @doc "A plan with every version (newest first) + each version's items."
+  def get_plan(id) do
+    case Repo.get(Plan, id) do
+      nil ->
+        nil
+
+      plan ->
+        versions =
+          from(v in PlanVersion, where: v.plan_id == ^plan.id, order_by: [desc: v.version])
+          |> Repo.all()
+          |> Repo.preload(:items)
+
+        %{plan | versions: versions}
+    end
+  end
+
   def create_plan(attrs) do
     %Plan{}
     |> Plan.changeset(attrs)
@@ -69,6 +85,48 @@ defmodule ArcadiaCloud.Catalog do
     |> Repo.insert()
   end
 
+  @doc """
+  Creates a new draft version of a plan together with its plan items, in
+  one transaction. The version number is assigned automatically. Pricing
+  edits are always a new version — never an in-place mutation — so
+  existing subscriptions keep the terms they signed up on.
+
+  `items` is a list of maps (string or atom keys) shaped like PlanItem.
+  Returns `{:ok, version}` (with items preloaded) or `{:error, changeset}`.
+  """
+  def create_plan_version(plan_id, attrs, items) when is_list(items) do
+    version_attrs =
+      attrs
+      |> Map.new(fn {k, v} -> {to_string(k), v} end)
+      |> Map.merge(%{
+        "plan_id" => plan_id,
+        "version" => next_version_number(plan_id),
+        "status" => "draft"
+      })
+
+    Repo.transaction(fn ->
+      version =
+        case %PlanVersion{} |> PlanVersion.changeset(version_attrs) |> Repo.insert() do
+          {:ok, v} -> v
+          {:error, cs} -> Repo.rollback(cs)
+        end
+
+      Enum.each(items, fn item ->
+        item_attrs =
+          item
+          |> Map.new(fn {k, v} -> {to_string(k), v} end)
+          |> Map.put("plan_version_id", version.id)
+
+        case %PlanItem{} |> PlanItem.changeset(item_attrs) |> Repo.insert() do
+          {:ok, _} -> :ok
+          {:error, cs} -> Repo.rollback(cs)
+        end
+      end)
+
+      get_version!(version.id)
+    end)
+  end
+
   @doc """
   Publishes a draft version: retires any currently-active version of the
   same plan, then flips this one to active.
diff --git a/lib/arcadia_cloud_web/controllers/catalog_controller.ex b/lib/arcadia_cloud_web/controllers/catalog_controller.ex
index 225259a..3339269 100644
--- a/lib/arcadia_cloud_web/controllers/catalog_controller.ex
+++ b/lib/arcadia_cloud_web/controllers/catalog_controller.ex
@@ -1,67 +1,185 @@
 defmodule ArcadiaCloudWeb.CatalogController do
   @moduledoc """
-  Read-only pricing catalog. Available to any authenticated tenant — the
-  catalog is what they pick a plan from. Pricing changes are operator
-  actions; no write endpoints here for MVP (seed/CLI only).
+  Pricing catalog. The list endpoints (`plans`, `addons`) are readable by
+  any authenticated tenant — that's what they pick a plan from.
+
+  The write endpoints are operator-only (platform-admin). Pricing is
+  versioned: you never edit a published plan in place. `create_version`
+  always makes a new DRAFT version; `publish_version` activates it and
+  retires the prior active one. Existing subscriptions keep the version
+  they were signed on until explicitly migrated.
   """
 
   use ArcadiaCloudWeb, :controller
 
   alias ArcadiaCloud.Catalog
 
+  # ---- reads ----------------------------------------------------------------
+
   def plans(conn, _params) do
     plans =
       Catalog.list_plans()
-      |> Enum.map(fn plan ->
-        version = Catalog.active_version(plan)
-        shape_plan(plan, version)
-      end)
+      |> Enum.map(fn plan -> shape_plan(plan, Catalog.active_version(plan)) end)
 
     json(conn, %{plans: plans})
   end
 
   def addons(conn, _params) do
-    addons =
-      Catalog.list_addons()
-      |> Enum.map(fn a ->
-        %{
-          code: a.code,
-          name: a.name,
-          resource_kind: a.resource_kind,
-          qty: a.qty,
-          price_cents: a.price_cents,
-          currency: a.currency
-        }
-      end)
+    json(conn, %{addons: Enum.map(Catalog.list_addons(), &shape_addon/1)})
+  end
 
-    json(conn, %{addons: addons})
+  @doc "Full plan detail incl. every version (draft/active/retired). Operator-only."
+  def show(conn, %{"id" => id}) do
+    with :ok <- require_platform_admin(conn) do
+      case Catalog.get_plan(id) do
+        nil ->
+          conn |> put_status(:not_found) |> json(%{error: "not_found"})
+
+        plan ->
+          json(conn, %{
+            plan: %{
+              id: plan.id,
+              code: plan.code,
+              name: plan.name,
+              description: plan.description,
+              active: plan.active,
+              versions: Enum.map(plan.versions, &shape_version/1)
+            }
+          })
+      end
+    end
+  end
+
+  # ---- writes (operator-only) -----------------------------------------------
+
+  def create_plan(conn, params) do
+    with :ok <- require_platform_admin(conn) do
+      case Catalog.create_plan(params) do
+        {:ok, plan} ->
+          conn |> put_status(:created) |> json(%{plan: shape_plan_bare(plan)})
+
+        {:error, changeset} ->
+          conn |> put_status(:unprocessable_entity) |> json(%{error: errors(changeset)})
+      end
+    end
+  end
+
+  def create_version(conn, %{"plan_id" => plan_id} = params) do
+    with :ok <- require_platform_admin(conn) do
+      attrs = Map.take(params, ["base_price_cents", "currency"])
+      items = params["items"] || []
+
+      case Catalog.create_plan_version(plan_id, attrs, items) do
+        {:ok, version} ->
+          conn |> put_status(:created) |> json(%{version: shape_version(version)})
+
+        {:error, changeset} ->
+          conn |> put_status(:unprocessable_entity) |> json(%{error: errors(changeset)})
+      end
+    end
+  end
+
+  def publish_version(conn, %{"id" => id}) do
+    with :ok <- require_platform_admin(conn) do
+      case Catalog.get_version(id) do
+        nil ->
+          conn |> put_status(:not_found) |> json(%{error: "not_found"})
+
+        %{status: "retired"} ->
+          conn
+          |> put_status(:unprocessable_entity)
+          |> json(%{error: "cannot publish a retired version"})
+
+        version ->
+          {:ok, published} = Catalog.publish_version(version)
+          json(conn, %{version: shape_version(Catalog.get_version!(published.id))})
+      end
+    end
+  end
+
+  def create_addon(conn, params) do
+    with :ok <- require_platform_admin(conn) do
+      case Catalog.create_addon(params) do
+        {:ok, addon} ->
+          conn |> put_status(:created) |> json(%{addon: shape_addon(addon)})
+
+        {:error, changeset} ->
+          conn |> put_status(:unprocessable_entity) |> json(%{error: errors(changeset)})
+      end
+    end
+  end
+
+  # ---- shaping --------------------------------------------------------------
+
+  defp shape_plan_bare(plan) do
+    %{id: plan.id, code: plan.code, name: plan.name, description: plan.description, active: plan.active}
   end
 
   defp shape_plan(plan, nil) do
-    %{code: plan.code, name: plan.name, description: plan.description, active_version: nil}
+    %{id: plan.id, code: plan.code, name: plan.name, description: plan.description, active_version: nil}
   end
 
   defp shape_plan(plan, version) do
     %{
+      id: plan.id,
       code: plan.code,
       name: plan.name,
       description: plan.description,
-      active_version: %{
-        id: version.id,
-        version: version.version,
-        base_price_cents: version.base_price_cents,
-        currency: version.currency,
-        items:
-          Enum.map(version.items, fn i ->
-            %{
-              resource_kind: i.resource_kind,
-              included_qty: i.included_qty,
-              overage_unit: i.overage_unit,
-              overage_price_cents: i.overage_price_cents,
-              hard_cap_qty: i.hard_cap_qty
-            }
-          end)
-      }
+      active_version: shape_version(version)
     }
   end
+
+  defp shape_version(v) do
+    %{
+      id: v.id,
+      version: v.version,
+      status: v.status,
+      base_price_cents: v.base_price_cents,
+      currency: v.currency,
+      published_at: v.published_at,
+      items: Enum.map(v.items, &shape_item/1)
+    }
+  end
+
+  defp shape_item(i) do
+    %{
+      resource_kind: i.resource_kind,
+      included_qty: i.included_qty,
+      overage_unit: i.overage_unit,
+      overage_price_cents: i.overage_price_cents,
+      hard_cap_qty: i.hard_cap_qty
+    }
+  end
+
+  defp shape_addon(a) do
+    %{
+      code: a.code,
+      name: a.name,
+      resource_kind: a.resource_kind,
+      qty: a.qty,
+      price_cents: a.price_cents,
+      currency: a.currency
+    }
+  end
+
+  # ---- helpers --------------------------------------------------------------
+
+  defp require_platform_admin(conn) do
+    identity = conn.assigns.current_identity
+
+    if is_list(identity.roles) and "platform-admin" in identity.roles do
+      :ok
+    else
+      conn
+      |> put_status(:forbidden)
+      |> json(%{error: "platform_admin_required"})
+      |> halt()
+    end
+  end
+
+  defp errors(changeset) do
+    Ecto.Changeset.traverse_errors(changeset, fn {msg, opts} ->
+      Enum.reduce(opts, msg, fn {k, v}, acc -> String.replace(acc, "%{#{k}}", to_string(v)) end)
+    end)
+  end
 end
diff --git a/lib/arcadia_cloud_web/router.ex b/lib/arcadia_cloud_web/router.ex
index d53a5c8..b9f4539 100644
--- a/lib/arcadia_cloud_web/router.ex
+++ b/lib/arcadia_cloud_web/router.ex
@@ -27,7 +27,12 @@ defmodule ArcadiaCloudWeb.Router do
     post "/drift/:id/accept", DriftController, :accept
 
     get "/catalog/plans", CatalogController, :plans
+    get "/catalog/plans/:id", CatalogController, :show
+    post "/catalog/plans", CatalogController, :create_plan
+    post "/catalog/plans/:plan_id/versions", CatalogController, :create_version
+    post "/catalog/versions/:id/publish", CatalogController, :publish_version
     get "/catalog/addons", CatalogController, :addons
+    post "/catalog/addons", CatalogController, :create_addon
 
     post "/quote", QuoteController, :create