diff --git a/changelog.d/1501-rail-pills.md b/changelog.d/1501-rail-pills.md
new file mode 100644
index 000000000..61d23a38b
--- /dev/null
+++ b/changelog.d/1501-rail-pills.md
@@ -0,0 +1,3 @@
+- The side panel rails show each panel as a labelled pill while no panel on
+  that side is open, and fold to icons once one opens. `UiRail` takes
+  `collapsible` for this (samehkhamis, #1501).
diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index e2f776810..c1c1ae770 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -1582,6 +1582,10 @@ Imagery (while shown), Street Level and Context on the right. Selecting an item
 opens its panel through `setPanelCollapsed(id, false, {explicit: true})`;
 selecting the open panel's item closes it. The item of the open panel is
 pressed (`aria-pressed`), and its tooltip is suppressed while the panel is open.
+While no panel on its side is open, the rail shows each item as a labelled pill
+(icon and title, `UiRail`'s `collapsible`); opening a panel folds the labels away
+to the icon rail. The rail is placed by its screen-side edge, so the pills grow
+toward the middle of the screen, over the closed side's empty corridor.
 
 One panel is open per desktop side, in every HUD layout. Opening a side panel
 by any route (rail, header, keyboard, voice) collapses its peers; restored or
diff --git a/src/ui/PanelRailView.vue b/src/ui/PanelRailView.vue
index 8f43dabb2..8ac9fb256 100644
--- a/src/ui/PanelRailView.vue
+++ b/src/ui/PanelRailView.vue
@@ -42,6 +42,7 @@ const label = computed(() =>
     :side="side"
     :label="label"
     :panel-open="active !== null"
+    collapsible
     @select="onSelect"
   />
 </template>
diff --git a/src/ui/kit/UiRail.test.mjs b/src/ui/kit/UiRail.test.mjs
index 6c443286a..57a0ff09d 100644
--- a/src/ui/kit/UiRail.test.mjs
+++ b/src/ui/kit/UiRail.test.mjs
@@ -71,3 +71,75 @@ test('tips open toward the screen, and not for the open panel', async () => {
   await other.trigger('focusout');
   assert.equal(wrapper.find('[role="tooltip"]').exists(), false);
 });
+
+test('a collapsible rail shows labelled pills until a panel opens', async () => {
+  const wrapper = mountRail({ collapsible: true });
+  const nav = wrapper.get('nav');
+  assert.ok(nav.classes().includes('ui-rail--collapsible'));
+  assert.ok(nav.classes().includes('ui-rail--expanded'));
+  assert.deepEqual(
+    wrapper.findAll('.ui-rail__label').map((label) => label.text()),
+    ['DATA LAYERS', 'AUTHORING', 'CCTV'],
+  );
+  // The label is on screen, so its tip would only repeat it.
+  await wrapper.findAll('.ui-tooltip')[0].trigger('focusin');
+  assert.equal(wrapper.find('[role="tooltip"]').exists(), false);
+  // The button keeps its own accessible name; the visible label is hidden
+  // from assistive technology so the name is not read twice.
+  const button = wrapper.get('[data-rail-item="layers"]');
+  assert.equal(button.attributes('aria-label'), 'DATA LAYERS');
+  assert.equal(button.get('.ui-rail__label').attributes('aria-hidden'), 'true');
+
+  await wrapper.setProps({ active: 'layers', panelOpen: true });
+  assert.ok(nav.classes().includes('ui-rail--collapsible'));
+  assert.equal(nav.classes().includes('ui-rail--expanded'), false);
+  // Collapsed, the other items' tips come back.
+  await wrapper.findAll('.ui-tooltip')[1].trigger('focusin');
+  await new Promise((resolve) => setTimeout(resolve, 450));
+  assert.equal(wrapper.get('[role="tooltip"]').text(), 'AUTHORING');
+});
+
+test('a label cut short by the pill keeps its tip', async (t) => {
+  const observers = [];
+  const original = globalThis.ResizeObserver;
+  globalThis.ResizeObserver = class {
+    constructor(callback) {
+      this.callback = callback;
+      this.targets = [];
+      observers.push(this);
+    }
+    observe(target) {
+      this.targets.push(target);
+    }
+    unobserve() {}
+    disconnect() {}
+  };
+  t.after(() => (globalThis.ResizeObserver = original));
+  const wrapper = mountRail({ collapsible: true });
+  const [observer] = observers;
+  const [layers, scenes] = observer.targets;
+  Object.defineProperties(layers, {
+    scrollWidth: { value: 260 },
+    clientWidth: { value: 220 },
+  });
+  Object.defineProperties(scenes, {
+    scrollWidth: { value: 90 },
+    clientWidth: { value: 90 },
+  });
+  observer.callback([{ target: layers }, { target: scenes }]);
+  await wrapper.vm.$nextTick();
+  await wrapper.findAll('.ui-tooltip')[0].trigger('focusin');
+  assert.equal(wrapper.get('[role="tooltip"]').text(), 'DATA LAYERS');
+  await wrapper.findAll('.ui-tooltip')[0].trigger('focusout');
+  await wrapper.findAll('.ui-tooltip')[1].trigger('focusin');
+  assert.equal(wrapper.find('[role="tooltip"]').exists(), false);
+});
+
+test('a plain rail has no labels', () => {
+  const wrapper = mountRail();
+  assert.equal(wrapper.find('.ui-rail__label').exists(), false);
+  assert.equal(
+    wrapper.get('nav').classes().includes('ui-rail--expanded'),
+    false,
+  );
+});
diff --git a/src/ui/kit/UiRail.vue b/src/ui/kit/UiRail.vue
index af740aae3..4e2bf6836 100644
--- a/src/ui/kit/UiRail.vue
+++ b/src/ui/kit/UiRail.vue
@@ -1,9 +1,10 @@
 <script setup>
+import { computed, onBeforeUnmount, reactive } from 'vue';
 import UiIcon from './UiIcon.vue';
 import UiTooltip from './UiTooltip.vue';
 import { RAIL_PANEL_OPEN_TOOLTIP_DELAY_MS } from './rail.js';
 
-defineProps({
+const props = defineProps({
   /** @type {import('vue').PropType<import('./rail.js').UiRailItem[]>} */
   items: { type: Array, required: true },
   /** The selected item's id, or null. */
@@ -17,18 +18,65 @@ defineProps({
    * panel's title, and the other tips wait for the pointer to rest.
    */
   panelOpen: { type: Boolean, default: false },
+  /**
+   * Show each item as a labelled pill while no panel is open, and collapse to
+   * icons once one is, making room for the panel.
+   */
+  collapsible: { type: Boolean, default: false },
 });
 const emit = defineEmits(['select']);
+const expanded = computed(() => props.collapsible && !props.panelOpen);
+
+// A label cut short by the pill's width keeps its tip, so the full name can
+// still be read. Each label is measured whenever its box changes size, which
+// includes the moment it settles after expanding.
+const truncated = reactive(new Set());
+const labelIds = new WeakMap();
+const labelElements = new Map();
+const labelObserver =
+  typeof ResizeObserver === 'function'
+    ? new ResizeObserver((entries) => {
+        for (const { target } of entries) {
+          const id = labelIds.get(target);
+          if (target.scrollWidth > target.clientWidth) truncated.add(id);
+          else truncated.delete(id);
+        }
+      })
+    : null;
+function trackLabel(id, element) {
+  const previous = labelElements.get(id);
+  if (previous === element) return;
+  if (previous) {
+    labelObserver?.unobserve(previous);
+    labelElements.delete(id);
+    truncated.delete(id);
+  }
+  if (!element) return;
+  labelElements.set(id, element);
+  labelIds.set(element, id);
+  labelObserver?.observe(element);
+}
+onBeforeUnmount(() => labelObserver?.disconnect());
+const tipHidden = (item) =>
+  (expanded.value && !truncated.has(item.id)) ||
+  (props.panelOpen && item.id === props.active);
 </script>
 
 <template>
-  <nav class="ui-rail" :class="`ui-rail--${side}`" :aria-label="label">
+  <nav
+    class="ui-rail"
+    :class="[
+      `ui-rail--${side}`,
+      { 'ui-rail--collapsible': collapsible, 'ui-rail--expanded': expanded },
+    ]"
+    :aria-label="label"
+  >
     <template v-for="item in items" :key="item.id">
       <i v-if="item.separatorBefore" class="ui-rail__sep" aria-hidden="true" />
       <UiTooltip
         :text="item.label"
         :side="side === 'left' ? 'right' : 'left'"
-        :disabled="panelOpen && item.id === active"
+        :disabled="tipHidden(item)"
         :delay="panelOpen ? RAIL_PANEL_OPEN_TOOLTIP_DELAY_MS : 0"
       >
         <button
@@ -42,6 +90,13 @@ const emit = defineEmits(['select']);
           @click="emit('select', item.id)"
         >
           <UiIcon :name="item.icon" />
+          <span
+            v-if="collapsible"
+            :ref="(element) => trackLabel(item.id, element)"
+            class="ui-rail__label"
+            aria-hidden="true"
+            >{{ item.label }}</span
+          >
           <span v-if="item.badge !== undefined" class="ui-rail__badge">{{
             item.badge
           }}</span>
diff --git a/src/ui/rtlLayout.test.mjs b/src/ui/rtlLayout.test.mjs
index a28ddcaa5..79341ad12 100644
--- a/src/ui/rtlLayout.test.mjs
+++ b/src/ui/rtlLayout.test.mjs
@@ -66,13 +66,19 @@ test('the Cyber cockpit keeps Data Layers on the left edge in every language', (
 
 test('the panel rails stay on the outer side of their stacks in right-to-left', () => {
   const layers = sheet('layers.css');
-  // Each rail is placed against its stack's outer edge; a physical side
-  // would put it over the panels once the stacks swap sides.
+  // Each rail is placed by its screen-side edge; a physical side would put
+  // it over the panels once the stacks swap sides.
   const left = ruleBody(layers, '.gev-panel-rail--left');
-  assert.match(left, /inset-inline-end: calc\(100% \+ 6px\);/);
+  assert.match(
+    left,
+    /inset-inline-start: calc\(-1 \* var\(--panel-rail-clearance\)\);/,
+  );
   assert.doesNotMatch(left, /(?:^|\s)(?:left|right):/);
   const right = ruleBody(layers, '.gev-panel-rail--right');
-  assert.match(right, /inset-inline-start: calc\(100% \+ 6px\);/);
+  assert.match(
+    right,
+    /inset-inline-end: calc\(-1 \* var\(--panel-rail-clearance\)\);/,
+  );
   assert.doesNotMatch(right, /(?:^|\s)(?:left|right):/);
   // Their tips open toward the middle of the screen.
   const kit = sheet('kit.css');
diff --git a/src/ui/styles/kit.css b/src/ui/styles/kit.css
index 4ceb796d7..0f1622c79 100644
--- a/src/ui/styles/kit.css
+++ b/src/ui/styles/kit.css
@@ -116,6 +116,51 @@
   opacity: 0.35;
   cursor: default;
 }
+
+/* A collapsible rail shows each item as an icon and its label while no panel
+   is open, and folds the labels away once one is. The collapsed item keeps
+   the plain rail's 32px square. */
+.ui-rail--collapsible {
+  transition: border-radius var(--transition-fast);
+}
+.ui-rail--collapsible .ui-rail__item {
+  display: flex;
+  align-items: center;
+  justify-content: flex-start;
+  width: 100%;
+  min-width: 32px;
+  padding: 0 6px;
+  transition:
+    color var(--transition-fast),
+    background var(--transition-fast),
+    border-color var(--transition-fast),
+    border-radius var(--transition-fast);
+}
+.ui-rail__label {
+  max-width: 0;
+  overflow: hidden;
+  opacity: 0;
+  white-space: nowrap;
+  text-overflow: ellipsis;
+  font: var(--dock-label-font-weight) var(--dock-label-font-size) / 1
+    var(--font-sans);
+  letter-spacing: var(--dock-label-letter-spacing);
+  transition:
+    max-width var(--transition-fast),
+    margin var(--transition-fast),
+    opacity var(--transition-fast);
+}
+.ui-rail--expanded {
+  border-radius: 21px;
+}
+.ui-rail--expanded .ui-rail__item {
+  border-radius: 16px;
+}
+.ui-rail--expanded .ui-rail__label {
+  max-width: 220px;
+  margin-inline: 8px 8px;
+  opacity: 1;
+}
 .ui-rail__badge {
   position: absolute;
   top: 1px;
diff --git a/src/ui/styles/layers.css b/src/ui/styles/layers.css
index 42e633754..51e4bfc8d 100644
--- a/src/ui/styles/layers.css
+++ b/src/ui/styles/layers.css
@@ -255,11 +255,14 @@
   pointer-events: auto;
   transition: top var(--transition-fast);
 }
+/* Each rail keeps its outer edge at the screen-side clearance, so a rail that
+   widens (labelled pills while its side has no open panel) grows toward the
+   middle of the screen. Collapsed, it sits 6px outside its stack. */
 .gev-panel-rail--left {
-  inset-inline-end: calc(100% + 6px);
+  inset-inline-start: calc(-1 * var(--panel-rail-clearance));
 }
 .gev-panel-rail--right {
-  inset-inline-start: calc(100% + 6px);
+  inset-inline-end: calc(-1 * var(--panel-rail-clearance));
 }
 body.mobile-shell #left-panel-stack > .gev-panel-rail,
 body.mobile-shell #right-context-rail > .gev-panel-rail,