diff --git a/codex/node.nim b/codex/node.nim
index d303a01c..482ed6f9 100644
--- a/codex/node.nim
+++ b/codex/node.nim
@@ -78,8 +78,7 @@ type
 
     # This will go into a download manager, likely persisted to disk
     # so download sessions can be live across node shutdowns.
-    downloads*: Table[uint64, Swarm]
-    downloadCounter: uint64
+    downloads*: Table[Cid, Swarm]
 
   CodexNodeRef* = ref CodexNode
 
@@ -100,28 +99,24 @@ func discovery*(self: CodexNodeRef): Discovery =
 
 proc startDownload*(
     self: CodexNodeRef, manifest: Manifest
-): Future[uint64] {.async: (raises: []).} =
+): Future[Cid] {.async: (raises: []).} =
   ## Start a download for a manifest
   ##
 
   # This won't play nice with multiple downloads as the Swarm will install
   # its own callbacks and listeners, but for experimentation is fine.
-  let
-    id = self.downloadCounter
-    swarm = Swarm.new(
-      manifest, self.networkStore.localStore, self.engine.network, self.discovery
-    )
-
-  self.downloadCounter += 1
-  self.downloads[id] = swarm
+  let swarm = Swarm.new(
+    manifest, self.networkStore.localStore, self.engine.network, self.discovery
+  )
 
+  self.downloads[manifest.treeCid] = swarm
   await swarm.start()
 
-  return id
+  return manifest.treeCid
 
-proc downloadStatus*(self: CodexNodeRef, id: uint64): ?(int, int) =
+proc downloadStatus*(self: CodexNodeRef, dataset: Cid): ?(int, int) =
   try:
-    return self.downloads[id].downloadStatus().some()
+    return self.downloads[dataset].downloadStatus().some()
   except KeyError:
     return none((int, int))
 
diff --git a/codex/rest/api.nim b/codex/rest/api.nim
index 1e2c4a3b..3b34aecc 100644
--- a/codex/rest/api.nim
+++ b/codex/rest/api.nim
@@ -207,18 +207,15 @@ proc initDataApi(node: CodexNodeRef, repoStore: RepoStore, router: var RestRoute
     info "Starting download for manifest",
       manifest = manifest.cid, treeCid = manifest.manifest.treeCid
 
-    let downloadId = await node.startDownload(manifest.manifest)
-
-    info "Download id assigned", downloadId = downloadId
-
+    let treeCid = await node.startDownload(manifest.manifest)
     return RestApiResponse.response(
-      $ %*{"downloadId": $downloadId}, contentType = "application/json"
+      $ %*{"downloadId": $treeCid}, contentType = "application/json"
     )
 
-  router.rawApi(MethodGet, "/api/codex/v1/download/{id}") do(
-    id: uint64
+  router.rawApi(MethodGet, "/api/codex/v1/download/{cid}") do(
+    cid: Cid
   ) -> RestApiResponse:
-    if (downloaded, total) =? node.downloadStatus(id.get()):
+    if (downloaded, total) =? node.downloadStatus(cid.get()):
       return RestApiResponse.response(
         $ %*{"downloaded": downloaded, "total": total}, contentType = "application/json"
       )