diff --git a/AGENTS.md b/AGENTS.md
index 552ab6f..6248a71 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -87,9 +87,9 @@ prints advisory observations (which never fail the build) when a project's decla
      pin a project's live and prerelease documentation to refs (`default`, `latest-stable`,
      `latest-prerelease`, or an explicit branch/tag). The default channel owns `/docs/<id>/`, the
      other is served at `/docs/<id>/<channel>/`, and `docsPage` resolves against the default channel.
-     Each channel is a first-class docs set — its own sidebar topic (`<Project> <version>`), its own
-     `/projects/<id>/<channel>/llms*.txt` bundle, and its own entry on the docs portal — because the
-     same product at another version is different documentation.
+     Each channel is a first-class docs set — its own page list (the sidebar lists the project once
+     but follows the version being read), its own `/projects/<id>/<channel>/llms*.txt` bundle, and
+     its own entry on the docs portal. The page switcher, not the sidebar, chooses the version.
      Only `github-path` supports two channels; `wiki`/`readme` have a single version. Promotion is
      automatic: the prerelease channel is withheld once a stable release (GitHub release or NuGet
      version) catches up with the prerelease line, and returns with the next prerelease — never
diff --git a/README.md b/README.md
index 0724716..33276e2 100644
--- a/README.md
+++ b/README.md
@@ -317,11 +317,13 @@ docs:
 
 The `live` channel is the default and keeps the canonical `/docs/<project>/`
 URLs; the `prerelease` channel is served at `/docs/<project>/prerelease/`.
-Versions are first-class: each published channel is its own sidebar topic
-(`ZodSharp 2.4.2`, `ZodSharp 3.0.0-prerelease.2`) with its own page list, its
-own machine-readable bundle, and its own entry on the documentation portal —
-same product, different version, therefore different docs. Every page also
-offers a switcher. Only `github-path` sources support two channels.
+Versions are first-class: each published version has its own page list, its own
+machine-readable bundle, and its own entry on the documentation portal — same
+product, different version, therefore different docs. The sidebar stays
+hierarchical, with one entry per project, and its page list follows the version
+you are reading. The version itself appears only in the page switcher, which is
+shown while two versions are published and names both. Only `github-path`
+sources support two channels.
 
 **Promotion is automatic.** The build publishes the prerelease channel only
 while a prerelease version outranks the newest stable release — comparing GitHub
diff --git a/docs/decisions/0009-documentation-channels.md b/docs/decisions/0009-documentation-channels.md
index dd52263..470a0de 100644
--- a/docs/decisions/0009-documentation-channels.md
+++ b/docs/decisions/0009-documentation-channels.md
@@ -149,12 +149,12 @@ history has to survive between builds, and an existing page is never overwritten
   while two channels are published: promotion withholds the prerelease channel,
   so the switcher disappears with it and nothing in the UI advertises a version
   that is no longer published (its retired URLs redirect instead).
-- The sidebar treats each channel as a **topic of its own**: `ZodSharp 2.4.2` and
-  `ZodSharp 3.0.0-prerelease.2` are separate entries in the topic picker, each
-  with a flat page list, exactly as two projects would be. A channel is a whole
-  documentation set, not a section of one, so grouping both under a single
-  project topic would claim one tree while the pages belong to two. A
-  single-channel project keeps the bare project name.
+- The sidebar keeps **one entry per project**. Each channel contributes its own
+  topic internally, so the page list always matches the version being read, but
+  every topic for a project carries the project's name and the topic picker
+  collapses the duplicates. A version is chosen with the page switcher and never
+  appears in the sidebar; the switcher exists only while two versions are
+  published.
 - Every published version has its own machine-readable bundle. The default
   channel keeps `/projects/<id>/llms.txt` and `llms-full.txt`; any other channel
   mirrors its documentation URL shape at
diff --git a/src/src/components/starlight/TopicSelect.astro b/src/src/components/starlight/TopicSelect.astro
index 6d2e463..86f9e84 100644
--- a/src/src/components/starlight/TopicSelect.astro
+++ b/src/src/components/starlight/TopicSelect.astro
@@ -4,13 +4,27 @@ const { topics, isPageWithTopic } = Astro.locals.starlightSidebarTopics;
 if (!isPageWithTopic) {
   return null;
 }
+
+// A project that publishes more than one documentation version contributes one
+// topic per version, each with the page list for that version — but the versions
+// belong in the page switcher, not in the topic list. Collapse topics that share
+// a label, preferring the one the reader is currently on so its link stays
+// correct. `Map` preserves insertion order, so the catalogue order is unchanged.
+const byLabel = new Map<string, (typeof topics)[number]>();
+for (const topic of topics) {
+  const existing = byLabel.get(topic.label);
+  if (!existing || (topic.isCurrent && !existing.isCurrent)) {
+    byLabel.set(topic.label, topic);
+  }
+}
+const projectTopics = [...byLabel.values()];
 ---
 
 <label class="topic-select">
   <span class="sr-only">Select documentation</span>
   <select onchange="window.location.assign(this.value)">
     {
-      topics.map((topic) => (
+      projectTopics.map((topic) => (
         <option value={topic.link} selected={topic.isCurrent}>
           {topic.label}
         </option>
diff --git a/src/src/lib/docs/channels.ts b/src/src/lib/docs/channels.ts
index 423ecd0..bf14a7d 100644
--- a/src/src/lib/docs/channels.ts
+++ b/src/src/lib/docs/channels.ts
@@ -433,13 +433,13 @@ export function channelDisplayLabel(channel: { id: DocChannelId; label: string }
 }
 
 /**
- * Sidebar topic label for one documentation version.
+ * Version-qualified label for one documentation version.
  *
- * Each channel is a first-class documentation set (ADR 0009), so a project that
- * publishes two channels appears as two topics — `ZodSharp 2.4.2` and
- * `ZodSharp 3.0.0-prerelease.2` — rather than as one topic that groups both
- * versions. The product name stays in front so the pair still reads as the same
- * product, and a single-channel project keeps its historical bare name.
+ * Used where two versions are listed as siblings — the documentation portal and
+ * the root `llms.txt` link list — so `ZodSharp 2.4.2` and
+ * `ZodSharp 3.0.0-prerelease.2` are distinguishable. The sidebar does **not**
+ * use it: there a project appears once, and the page switcher chooses the
+ * version. A single-channel project keeps the bare project name.
  */
 export function channelTopicLabel(
   projectName: string,
diff --git a/src/src/lib/docs/sidebar.ts b/src/src/lib/docs/sidebar.ts
index cbc4042..159a0b7 100644
--- a/src/src/lib/docs/sidebar.ts
+++ b/src/src/lib/docs/sidebar.ts
@@ -1,7 +1,7 @@
 import type { ResolvedProject } from '../manifest/load';
 import type { DocsManifest, DocsManifestChannel } from './aggregate';
 
-import { channelBasePath, channelTopicLabel } from './channels';
+import { channelBasePath } from './channels';
 
 export interface SidebarSlugEntry {
   label?: string;
@@ -53,14 +53,12 @@ export function buildChannelItems(
 /**
  * Build the sidebar topics for a single project's documentation.
  *
- * A channel is a whole documentation set, not a section of one: the same
- * product at a different version has different pages, different links and its
- * own `llms.txt`. Grouping the channels inside one topic would make the sidebar
- * claim a single tree while the pages belong to two, and it would bury the
- * second version behind a collapsed group. Each channel therefore becomes its
- * own topic — `ZodSharp 2.4.2` and `ZodSharp 3.0.0-prerelease.2` — with a flat
- * item list, so switching versions works exactly like switching projects.
- * A single-channel project keeps its historical topic (the bare project name).
+ * A channel is a whole documentation set, so each published version contributes
+ * its own topic and its own page list — the sidebar must describe the version
+ * the reader is on. The versions are **not** shown in the sidebar, though: every
+ * topic for a project carries the project's name, and the topic picker collapses
+ * the duplicates (see `TopicSelect.astro`). Choosing a version is the job of the
+ * page switcher, which only appears while two versions are published.
  */
 export function buildProjectTopics(
   project: ResolvedProject,
@@ -78,7 +76,7 @@ export function buildProjectTopics(
   return ordered
     .map((channel) => ({
       id: channels.length > 1 ? `${project.id}-${channel.id}` : project.id,
-      label: channelTopicLabel(project.name, channel, channels.length),
+      label: project.name,
       link: channelBasePath(project.id, channel.id, channel.default),
       items: buildChannelItems(project.id, channel),
     }))
diff --git a/src/src/pages/docs/index.astro b/src/src/pages/docs/index.astro
index 178b088..f24697a 100644
--- a/src/src/pages/docs/index.astro
+++ b/src/src/pages/docs/index.astro
@@ -82,9 +82,8 @@ const pageCount = docsManifest?.projects.reduce(
           <h2 class="text-xl font-semibold">Documentation versions</h2>
           <p class="mt-3 max-w-3xl text-sm text-muted">
             Some projects publish more than one version of their documentation. Each version is a
-            documentation set in its own right — its own pages, its own sidebar entry and its own
-            machine-readable bundle — because installing a different version means reading different
-            docs.
+            documentation set in its own right — its own pages and its own machine-readable bundle —
+            because installing a different version means reading different docs.
           </p>
           <ul class="mt-5 space-y-5">
             {versionedProjects.map(({ project, channels }) => (
diff --git a/src/tests/dist/built-output.test.ts b/src/tests/dist/built-output.test.ts
index 15cf035..b146962 100644
--- a/src/tests/dist/built-output.test.ts
+++ b/src/tests/dist/built-output.test.ts
@@ -447,15 +447,27 @@ describe('built documentation channels', () => {
     }
   });
 
-  test.skipIf(!prerelease)('each documentation version is its own sidebar topic', () => {
-    // Versions are distinct sidebar entries, not groups inside one project
-    // topic: the same product, two documentation sets. The topic picker lists
-    // both, each pointing at its own landing page.
+  test.skipIf(!prerelease)('the sidebar lists the project once and hides the versions', () => {
+    // The reader is on the prerelease version: its page list is the sidebar
+    // body, but the topic picker still lists `ZodSharp` exactly once and no
+    // version label appears in any option.
     const content = requireBuilt(prereleaseIndex);
-    expect(content).toContain(`ZodSharp ${live!.label}`);
-    expect(content).toContain(`ZodSharp ${prerelease!.label}`);
-    expect(content).toContain('value="/docs/zodsharp/"');
-    expect(content).toContain('value="/docs/zodsharp/prerelease/"');
+    const optionLabels = [...content.matchAll(/<option[^>]*>([^<]*)<\/option>/g)].map((match) =>
+      (match[1] ?? '').trim(),
+    );
+    expect(optionLabels).toContain('ZodSharp');
+    expect(optionLabels.some((label) => label.includes(live!.label))).toBe(false);
+    expect(optionLabels.some((label) => label.includes(prerelease!.label))).toBe(false);
+    expect((content.match(/value="\/docs\/zodsharp/g) ?? []).length).toBe(1);
+
+    // The page switcher is the only place versions appear, and it shows both.
+    expect(content).toContain(channelDisplayLabel(live!));
+    expect(content).toContain(channelDisplayLabel(prerelease!));
+  });
+
+  test('the version switcher only appears while a second version is published', () => {
+    // A single-channel project has no version to choose.
+    expect(requireBuilt('docs/results/index.html')).not.toContain('doc-channel-menu');
   });
 
   test.skipIf(!prerelease)('each documentation version publishes its own llms bundles', () => {
diff --git a/src/tests/unit/docs-sidebar.test.ts b/src/tests/unit/docs-sidebar.test.ts
index 70a0334..644ebeb 100644
--- a/src/tests/unit/docs-sidebar.test.ts
+++ b/src/tests/unit/docs-sidebar.test.ts
@@ -66,12 +66,12 @@ describe('documentation sidebar topics', () => {
     ]);
   });
 
-  test('each published version is its own topic, not a group inside one', () => {
+  test('a versioned project still reads as one project in the sidebar', () => {
     const topics = buildProjectTopics(project!, bothChannels());
-    expect(topics.map((topic) => topic.label)).toEqual([
-      'ZodSharp 2.4.2',
-      'ZodSharp 3.0.0-prerelease.2',
-    ]);
+    // One topic per version internally (each with that version's pages), but
+    // every topic carries the project name: versions never leak into the
+    // sidebar — the page switcher is where a reader chooses one.
+    expect(topics.map((topic) => topic.label)).toEqual(['ZodSharp', 'ZodSharp']);
     expect(topics.map((topic) => topic.link)).toEqual([
       '/docs/zodsharp/',
       '/docs/zodsharp/prerelease/',
@@ -79,6 +79,13 @@ describe('documentation sidebar topics', () => {
     expect(topics.map((topic) => topic.id)).toEqual(['zodsharp-live', 'zodsharp-prerelease']);
   });
 
+  test('the sidebar never names a version', () => {
+    for (const topic of buildProjectTopics(project!, bothChannels())) {
+      expect(topic.label).not.toContain('2.4.2');
+      expect(topic.label).not.toContain('3.0.0');
+    }
+  });
+
   test('the two versions never share a page or a group', () => {
     const [live, prerelease] = buildProjectTopics(project!, bothChannels());
     const liveSlugs = new Set(live!.items.map((item) => item.slug));