diff --git a/apps/desktop/electron/main.ts b/apps/desktop/electron/main.ts
index 4a2c1ce6c8c..ce8aa7d8382 100644
--- a/apps/desktop/electron/main.ts
+++ b/apps/desktop/electron/main.ts
@@ -11069,7 +11069,7 @@ function resolveHermesVersionInfo() {
       baseVersion: INSTALL_STAMP.baseVersion ?? undefined,
       distance: INSTALL_STAMP.distance ?? undefined,
       commit: INSTALL_STAMP.commit,
-      branch: INSTALL_STAMP.branch ?? undefined,
+      branch: INSTALL_STAMP.branch,
       source: INSTALL_STAMP.source ?? undefined,
       installMethod: INSTALL_STAMP.installMethod ?? undefined,
       dirty: INSTALL_STAMP.dirty
diff --git a/apps/desktop/src/components/version-details.test.tsx b/apps/desktop/src/components/version-details.test.tsx
new file mode 100644
index 00000000000..a720d80d565
--- /dev/null
+++ b/apps/desktop/src/components/version-details.test.tsx
@@ -0,0 +1,41 @@
+import { cleanup, render, screen } from '@testing-library/react'
+import { afterEach, describe, expect, it } from 'vitest'
+
+import type { DesktopVersionInfo } from '@/global'
+import { I18nProvider } from '@/i18n'
+
+import { VersionDetails } from './version-details'
+
+const baseVersion: DesktopVersionInfo = {
+  appVersion: '0.19.0',
+  electronVersion: '37.0.0',
+  hermesRoot: '/tmp/hermes',
+  nodeVersion: '22.0.0',
+  platform: 'linux'
+}
+
+afterEach(cleanup)
+
+describe('VersionDetails', () => {
+  it('labels a missing branch explicitly', () => {
+    render(
+      <I18nProvider configClient={null} initialLocale="en">
+        <VersionDetails version={{ ...baseVersion, branch: null }} />
+      </I18nProvider>
+    )
+
+    expect(screen.getByText('Branch')).toBeTruthy()
+    expect(screen.getByText('No branch information')).toBeTruthy()
+  })
+
+  it('preserves a literal branch named unknown', () => {
+    render(
+      <I18nProvider configClient={null} initialLocale="en">
+        <VersionDetails version={{ ...baseVersion, branch: 'unknown' }} />
+      </I18nProvider>
+    )
+
+    expect(screen.getByText('unknown')).toBeTruthy()
+    expect(screen.queryByText('No branch information')).toBeNull()
+  })
+})
diff --git a/apps/desktop/src/components/version-details.tsx b/apps/desktop/src/components/version-details.tsx
index 2e6f24e76bc..498ace7ede2 100644
--- a/apps/desktop/src/components/version-details.tsx
+++ b/apps/desktop/src/components/version-details.tsx
@@ -25,12 +25,10 @@ export function VersionDetails({ version }: { version: DesktopVersionInfo }) {
           <dd>{version.baseVersion}</dd>
         </div>
       )}
-      {version.branch && (
-        <div className="flex justify-between gap-4">
-          <dt className="text-muted-foreground">{u.versionDetailsBranch}</dt>
-          <dd className="break-all text-right">{version.branch}</dd>
-        </div>
-      )}
+      <div className="flex justify-between gap-4">
+        <dt className="text-muted-foreground">{u.versionDetailsBranch}</dt>
+        <dd className="break-all text-right">{version.branch ?? u.versionDetailsNoBranchInfo}</dd>
+      </div>
       {version.commit && (
         <div className="flex justify-between gap-4">
           <dt className="text-muted-foreground">{u.versionDetailsCommit}</dt>
diff --git a/apps/desktop/src/global.d.ts b/apps/desktop/src/global.d.ts
index 3b4f4f1c305..241d558e23d 100644
--- a/apps/desktop/src/global.d.ts
+++ b/apps/desktop/src/global.d.ts
@@ -320,7 +320,7 @@ export interface HermesTerminalExit {
 export interface DesktopVersionInfo {
   appVersion: string
   baseVersion?: string
-  branch?: string
+  branch?: string | null
   commit?: string
   distance?: number
   dirty?: boolean
diff --git a/apps/desktop/src/i18n/en.ts b/apps/desktop/src/i18n/en.ts
index f33335a990e..6746449611b 100644
--- a/apps/desktop/src/i18n/en.ts
+++ b/apps/desktop/src/i18n/en.ts
@@ -2132,6 +2132,7 @@ export const en: Translations = {
     versionDetailsVersion: 'Version',
     versionDetailsBaseVersion: 'Release version',
     versionDetailsBranch: 'Branch',
+    versionDetailsNoBranchInfo: 'No branch information',
     versionDetailsCommit: 'Commit',
     versionDetailsDirty: 'This package was built from a dirty source tree.',
     versionDetailsDirtyUnknown: 'Built from a dirty source tree. The number of changes since the last release is unknown.',
diff --git a/apps/desktop/src/i18n/ja.ts b/apps/desktop/src/i18n/ja.ts
index 2d16d792ec5..6bbc48ba4cb 100644
--- a/apps/desktop/src/i18n/ja.ts
+++ b/apps/desktop/src/i18n/ja.ts
@@ -1992,6 +1992,7 @@ export const ja = defineLocale({
     versionDetailsVersion: 'バージョン',
     versionDetailsBaseVersion: 'リリースバージョン',
     versionDetailsBranch: 'ブランチ',
+    versionDetailsNoBranchInfo: 'ブランチ情報なし',
     versionDetailsCommit: 'コミット',
     versionDetailsDirty: 'このパッケージは変更のあるソースツリーからビルドされました。',
     versionDetailsDirtyUnknown: '変更のあるソースツリーからビルドされました。最後のリリースからの変更数は不明です。',
diff --git a/apps/desktop/src/i18n/types.ts b/apps/desktop/src/i18n/types.ts
index 8039339c24d..6d7211ec1eb 100644
--- a/apps/desktop/src/i18n/types.ts
+++ b/apps/desktop/src/i18n/types.ts
@@ -1771,6 +1771,7 @@ export interface Translations {
     versionDetailsVersion: string
     versionDetailsBaseVersion: string
     versionDetailsBranch: string
+    versionDetailsNoBranchInfo: string
     versionDetailsCommit: string
     versionDetailsDirty: string
     versionDetailsDirtyUnknown: string
diff --git a/apps/desktop/src/i18n/zh-hant.ts b/apps/desktop/src/i18n/zh-hant.ts
index d55d46c2559..5b372a113c5 100644
--- a/apps/desktop/src/i18n/zh-hant.ts
+++ b/apps/desktop/src/i18n/zh-hant.ts
@@ -1932,6 +1932,7 @@ export const zhHant = defineLocale({
     versionDetailsVersion: '版本',
     versionDetailsBaseVersion: '發行版本',
     versionDetailsBranch: '分支',
+    versionDetailsNoBranchInfo: '沒有分支資訊',
     versionDetailsCommit: '提交',
     versionDetailsDirty: '此套件從有未提交變更的來源樹建置。',
     versionDetailsDirtyUnknown: '從有未提交變更的來源樹建置。自上次發布以來的變更數量未知。',
diff --git a/apps/desktop/src/i18n/zh.ts b/apps/desktop/src/i18n/zh.ts
index fd116f3f247..d8b05bfe5b5 100644
--- a/apps/desktop/src/i18n/zh.ts
+++ b/apps/desktop/src/i18n/zh.ts
@@ -2323,6 +2323,7 @@ export const zh: Translations = {
     versionDetailsVersion: '版本',
     versionDetailsBaseVersion: '发布版本',
     versionDetailsBranch: '分支',
+    versionDetailsNoBranchInfo: '无分支信息',
     versionDetailsCommit: '提交',
     versionDetailsDirty: '此软件包从有未提交更改的源代码树构建。',
     versionDetailsDirtyUnknown: '从有未提交更改的源代码树构建。自上次发布以来的更改数量未知。',
diff --git a/nix/desktop.nix b/nix/desktop.nix
index 430e3860ba1..b71a7a5aab0 100644
--- a/nix/desktop.nix
+++ b/nix/desktop.nix
@@ -44,10 +44,6 @@ let
     if distance != null && distance > 0 then "${version}+${toString distance}"
     else if dirty && distance == null then "${version}+?"
     else version;
-  # On a dirty tree, sourceInfo.ref is null (flakes can't determine the ref).
-  # Show "unknown" rather than null so the desktop doesn't fall back to its
-  # self-update default branch ("main") when the real branch is unavailable.
-  branchLabel = if branch != null then branch else "unknown";
 
   electronHeaders = pkgs.fetchurl {
     url = "https://artifacts.electronjs.org/headers/dist/v${electron.version}/node-v${electron.version}-headers.tar.gz";
@@ -166,7 +162,7 @@ let
         cp -rn apps/desktop/dist $out/
 
         cat > $out/install-stamp.json <<'EOF'
-        {"schemaVersion":2,"commit":${builtins.toJSON rev},"branch":${builtins.toJSON branchLabel},"baseVersion":"${version}","displayVersion":"${displayVersion}","distance":${builtins.toJSON distance},"dirty":${
+        {"schemaVersion":2,"commit":${builtins.toJSON rev},"branch":${builtins.toJSON branch},"baseVersion":"${version}","displayVersion":"${displayVersion}","distance":${builtins.toJSON distance},"dirty":${
           if dirty then "true" else "false"
         },"source":"nix","installMethod":"nix"}
         EOF
diff --git a/nix/hermes-agent.nix b/nix/hermes-agent.nix
index 228df8f24c5..c84fd4604aa 100644
--- a/nix/hermes-agent.nix
+++ b/nix/hermes-agent.nix
@@ -56,7 +56,6 @@ let
     if stampDistance != null && stampDistance > 0 then "${version}+${toString stampDistance}"
     else if dirty && stampDistance == null then "${version}+?"
     else version;
-  stampBranch = if branch != null then branch else "unknown";
 
   nodejs = nodejs_22;
   mkHermesVenv =
@@ -206,7 +205,7 @@ stdenv.mkDerivation (finalAttrs: {
     # runtime instead of probing env vars or .git — one file, one source
     # of truth for the Python runtime (CLI, TUI).
     cat > $out/share/hermes-agent/.hermes_build_info.json <<STAMP
-    {"schemaVersion":2,"commit":${builtins.toJSON rev},"commitDate":${builtins.toJSON lastModified},"branch":${builtins.toJSON stampBranch},"baseVersion":"${version}","displayVersion":"${stampDisplayVersion}","distance":${builtins.toJSON stampDistance},"dirty":${if dirty then "true" else "false"},"source":"nix"}
+    {"schemaVersion":2,"commit":${builtins.toJSON rev},"commitDate":${builtins.toJSON lastModified},"branch":${builtins.toJSON branch},"baseVersion":"${version}","displayVersion":"${stampDisplayVersion}","distance":${builtins.toJSON stampDistance},"dirty":${if dirty then "true" else "false"},"source":"nix"}
     STAMP
 
     ${lib.concatMapStringsSep "\n"
diff --git a/nix/packages.nix b/nix/packages.nix
index fad5b0522f7..dc9ef6079c1 100644
--- a/nix/packages.nix
+++ b/nix/packages.nix
@@ -12,8 +12,10 @@
       dirtyRevision = inputs.self.dirtyRev or null;
       # inputs.self.sourceInfo is a string (store path) in current Nix, not a
       # record. The metadata fields are available as top-level attributes on
-      # inputs.self directly: rev, dirtyRev, lastModified, ref, revCount.
-      # On dirty trees ref/rev/revCount are null; dirtyRev is set.
+      # inputs.self directly. A flake URL's requested ref is intentionally not
+      # exposed as self.ref after Nix resolves it to an immutable source, so
+      # branch is normally null for remote flakes. Preserve null rather than
+      # inventing a sentinel that could be a real branch name.
       rev = inputs.self.rev or (if dirtyRevision != null then builtins.substring 0 40 dirtyRevision else null);
       revCount = inputs.self.revCount or null;
       rawRef = inputs.self.ref or null;
diff --git a/scripts/write_install_stamp.py b/scripts/write_install_stamp.py
index c2be750e827..d450d17cd6d 100644
--- a/scripts/write_install_stamp.py
+++ b/scripts/write_install_stamp.py
@@ -153,8 +153,6 @@ def build_stamp(
         branch = _resolve_branch_from_env()
     if branch is None:
         branch = _resolve_branch_from_git()
-    if branch is None:
-        branch = "unknown"
 
     # Dirty: explicit > git
     if dirty is None:
diff --git a/tests/hermes_cli/test_version_info.py b/tests/hermes_cli/test_version_info.py
index 2b1cada5c57..4a23f771a05 100644
--- a/tests/hermes_cli/test_version_info.py
+++ b/tests/hermes_cli/test_version_info.py
@@ -47,11 +47,11 @@ def test_stamp_version_info_reads_nix_stamp(tmp_path, monkeypatch):
     assert info == VersionInfo("0.19.0", "0.19.0+3", 3, "a" * 40, "feature/version", "nix")
 
 
-def test_stamp_version_info_reads_docker_stamp_with_unknown_distance(tmp_path, monkeypatch):
+def test_stamp_version_info_preserves_missing_branch(tmp_path, monkeypatch):
     stamp = {
         "schemaVersion": 2,
         "commit": "b" * 40,
-        "branch": "unknown",
+        "branch": None,
         "baseVersion": "0.19.0",
         "displayVersion": "0.19.0+?",
         "distance": None,
@@ -64,7 +64,7 @@ def test_stamp_version_info_reads_docker_stamp_with_unknown_distance(tmp_path, m
 
     info = get_version_info()
 
-    assert info == VersionInfo("0.19.0", "0.19.0+?", None, "b" * 40, "unknown", "docker", True)
+    assert info == VersionInfo("0.19.0", "0.19.0+?", None, "b" * 40, None, "docker", True)
 
 
 def test_stamp_version_info_ignores_fallback_commit(tmp_path, monkeypatch):