diff --git a/client/src/components/Chat/Messages/Content/Parts/Thinking.tsx b/client/src/components/Chat/Messages/Content/Parts/Thinking.tsx
index 3be18b6056..6e142c11e8 100644
--- a/client/src/components/Chat/Messages/Content/Parts/Thinking.tsx
+++ b/client/src/components/Chat/Messages/Content/Parts/Thinking.tsx
@@ -98,12 +98,19 @@ export const ThinkingButton = memo(
               aria-hidden="true"
             />
           </span>
-          {/* The entrance and the shimmer both drive `animation-name`, so they
-              cannot share an element — and the nesting order is not a free
-              choice either. The clipped element paints the glyphs itself, so a
-              descendant's opacity cannot fade them: entrance outside and
-              shimmer inside fades correctly, while the reverse leaves the label
-              fully lit right through its own fade.
+          {/* The sweep rides the label row itself. That row is a flex item, so
+              `.shimmer`'s `inline-block` is blockified away and the text sits
+              exactly where the un-shimmered label sits — which matters, because
+              an `inline-block` carrying `truncate` takes its baseline from its
+              bottom margin edge, growing the line box and lifting the label off
+              the icon's axis.
+
+              Only the generated-label entrance forces a nested span: it and the
+              sweep both drive `animation-name`, so they cannot share an element.
+              There the entrance must stay outside — the clipped element paints
+              the glyphs itself, so a descendant's opacity cannot fade them — and
+              the inner span takes `align-top` to keep the baseline rule above
+              from reopening the same gap.
 
               `key` remounts the row so the entrance replays, and that restarts
               the sweep with it. Reasoning labels revise on a 3s default against
@@ -114,11 +121,16 @@ export const ThinkingButton = memo(
             key={animateLabel ? label : undefined}
             className={cn(
               'min-w-0 truncate text-left',
+              shimmerLabel && !animateLabel && 'shimmer',
               animateLabel &&
                 'duration-300 ease-out animate-in fade-in-0 slide-in-from-bottom-1 motion-reduce:animate-none',
             )}
           >
-            {shimmerLabel ? <span className="shimmer max-w-full truncate">{label}</span> : label}
+            {shimmerLabel && animateLabel ? (
+              <span className="shimmer max-w-full truncate align-top">{label}</span>
+            ) : (
+              label
+            )}
           </span>
         </button>
         {content && showCopyButton && (
diff --git a/client/src/components/Chat/Messages/Content/Parts/__tests__/Reasoning.spec.tsx b/client/src/components/Chat/Messages/Content/Parts/__tests__/Reasoning.spec.tsx
index 8c1c506e21..6a77cca744 100644
--- a/client/src/components/Chat/Messages/Content/Parts/__tests__/Reasoning.spec.tsx
+++ b/client/src/components/Chat/Messages/Content/Parts/__tests__/Reasoning.spec.tsx
@@ -27,6 +27,19 @@ describe('Reasoning label shimmer', () => {
     expect(screen.getByText('Thinking...')).toHaveClass('shimmer');
   });
 
+  /** The sweep has to ride the label row itself rather than a span nested inside
+   *  it. That row is a flex item, so `.shimmer`'s `inline-block` is blockified
+   *  away; nested, it is an inline-block whose `truncate` moves its baseline to
+   *  its bottom margin edge, which grew the line box 18px -> 23px and lifted the
+   *  label 2px off the lightbulb's axis for the whole of a generation. */
+  it('keeps the sweep on the label row instead of a nested span', () => {
+    renderReasoning();
+    const label = screen.getByText('Thinking...');
+
+    expect(label).toHaveClass('truncate');
+    expect(label.querySelector('.shimmer')).toBeNull();
+  });
+
   it('leaves settled thoughts unanimated', () => {
     renderReasoning({ isSubmitting: false });
     expect(screen.getByText('Thoughts')).not.toHaveClass('shimmer');