diff --git a/apps/web/src/lib/gcodeVisualizer.ts b/apps/web/src/lib/gcodeVisualizer.ts
index d481005a7..025b7ef01 100644
--- a/apps/web/src/lib/gcodeVisualizer.ts
+++ b/apps/web/src/lib/gcodeVisualizer.ts
@@ -11,6 +11,13 @@ const motionColor = {
   'G3': new Color(colornames('deepskyblue') as string)
 }
 
+// Minimum squared distance between consecutive vertices (mm²).
+// Vertices closer than this are skipped during visualization to avoid
+// creating huge geometry for files with tiny XY movements (e.g. continuous
+// A-axis rotation programs where XYZ barely changes between lines).
+// 0.1mm is sub-pixel at typical CNC visualization zoom levels.
+const MIN_DISTANCE_SQ = 0.1 * 0.1
+
 export interface GCodeFrame {
   data: string
   vertexIndex: number
@@ -31,43 +38,53 @@ let _cachedGcodeInput: string | null = null
 let _cachedGcodeResult: GCodeGeometryResult | null = null
 
 /**
- * Process G-code string and generate Three.js BufferGeometry for visualization.
- * Results are cached - repeated calls with the same gcode string return the cached result.
+ * Shared parsing logic used by both sync and async code paths.
+ * Creates a Toolpath instance with addLine/addArcCurve callbacks that apply
+ * vertex decimation - skipping vertices within MIN_DISTANCE_SQ of the previous one.
  *
- * @param gcode - G-code string to process
- * @returns Geometry data with frames for animation/stepping through the toolpath
+ * Returns the toolpath interpreter and the arrays it populates.
  */
-export function processGCode(gcode: string | null | undefined): GCodeGeometryResult | null {
-  if (!gcode) {
-    return null
-  }
-
-  // Return cached result if input hasn't changed
-  if (gcode === _cachedGcodeInput && _cachedGcodeResult) {
-    return _cachedGcodeResult
-  }
-
+function createDecimatedToolpath() {
   const positions: number[] = []
   const colors: number[] = []
   const frames: GCodeFrame[] = []
-  let initialPosition: Vector3 | undefined = undefined // Track the toolpath origin (v1 from first addLine call)
+  let initialPosition: Vector3 | undefined = undefined
+
+  // Decimation state - tracks the last emitted vertex for distance checks
+  let lastX = NaN
+  let lastY = NaN
+  let lastZ = NaN
+  let lastMotion: string | undefined = undefined
 
-  // Create toolpath processor with callbacks
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   const toolpath: any = new (Toolpath as any)({
     // Called for each line segment (G0, G1 moves)
-    // Note: The toolpath library ensures continuity - v1 of current line = v2 of previous line
-    // So we only push v2 (the endpoint), not v1 - matching legacy implementation
     addLine: (modal: { motion?: string }, v1: { x: number; y: number; z: number }, v2: { x: number; y: number; z: number }) => {
       const { motion } = modal
       const color = motion ? (motionColor[motion as keyof typeof motionColor] || defaultColor) : defaultColor
-      
+
       // Capture the initial position from the first move's start point (v1)
       if (initialPosition === undefined) {
         initialPosition = new Vector3(v1.x, v1.y, v1.z)
       }
-      
-      // Only push the endpoint - matching legacy code exactly
+
+      // Vertex decimation: skip points too close to the previous vertex.
+      // Always keep vertex when motion type changes (G0↔G1 transitions)
+      // to preserve color boundaries in the polyline.
+      const dx = v2.x - lastX
+      const dy = v2.y - lastY
+      const dz = v2.z - lastZ
+      const distSq = dx * dx + dy * dy + dz * dz
+
+      if (distSq < MIN_DISTANCE_SQ && motion === lastMotion) {
+        return
+      }
+
+      lastX = v2.x
+      lastY = v2.y
+      lastZ = v2.z
+      lastMotion = motion
+
       positions.push(v2.x, v2.y, v2.z)
       colors.push(color.r, color.g, color.b)
     },
@@ -80,7 +97,7 @@ export function processGCode(gcode: string | null | undefined): GCodeGeometryRes
       v0: { x: number; y: number; z: number }
     ) => {
       const { motion, plane } = modal
-      
+
       // Capture the initial position from the first arc's start point (v1) if not already set
       if (initialPosition === undefined) {
         initialPosition = new Vector3(v1.x, v1.y, v1.z)
@@ -97,8 +114,6 @@ export function processGCode(gcode: string | null | undefined): GCodeGeometryRes
         endAngle += (2 * Math.PI)
       }
 
-      // Use THREE.ArcCurve to properly handle clockwise/counterclockwise arcs
-      // This matches the legacy implementation exactly
       const arcCurve = new ArcCurve(
         v0.x, // aX
         v0.y, // aY
@@ -115,39 +130,58 @@ export function processGCode(gcode: string | null | undefined): GCodeGeometryRes
         const point = points[i]
         const z = v1.z + ((v2.z - v1.z) / points.length) * i
 
+        let px: number, py: number, pz: number
         if (plane === 'G17') { // XY-plane
-          positions.push(point.x, point.y, z)
+          px = point.x; py = point.y; pz = z
         } else if (plane === 'G18') { // ZX-plane
-          positions.push(point.y, z, point.x)
+          px = point.y; py = z; pz = point.x
         } else if (plane === 'G19') { // YZ-plane
-          positions.push(z, point.x, point.y)
+          px = z; py = point.x; pz = point.y
         } else {
-          // Default to XY-plane if plane is not specified
-          positions.push(point.x, point.y, z)
+          px = point.x; py = point.y; pz = z
+        }
+
+        // Apply decimation to arc points too, but always keep the last
+        // point of each arc for continuity with the next segment
+        const isLast = (i === points.length - 1)
+        if (!isLast) {
+          const adx = px - lastX
+          const ady = py - lastY
+          const adz = pz - lastZ
+          if (adx * adx + ady * ady + adz * adz < MIN_DISTANCE_SQ) {
+            continue
+          }
         }
+
+        lastX = px
+        lastY = py
+        lastZ = pz
+
+        positions.push(px, py, pz)
         colors.push(color.r, color.g, color.b)
       }
+
+      lastMotion = motion
     }
   })
 
-  // Process G-code synchronously
-  // Call method directly on toolpath instance to preserve 'this' context
-  if (toolpath && typeof (toolpath as { loadFromStringSync?: (gcode: string, callback: (line: string) => void) => void }).loadFromStringSync === 'function') {
-    (toolpath as { loadFromStringSync: (gcode: string, callback: (line: string) => void) => void }).loadFromStringSync(gcode, (line: string) => {
-      frames.push({
-        data: line,
-        vertexIndex: Math.floor(positions.length / 3) // Current vertex count
-      })
-    })
-  }
+  return { toolpath, positions, colors, frames, getInitialPosition: () => initialPosition }
+}
 
-  // Create BufferGeometry
+/**
+ * Build a GCodeGeometryResult from raw position/color/frame arrays.
+ */
+function buildGeometryResult(
+  positions: number[],
+  colors: number[],
+  frames: GCodeFrame[],
+  initialPosition: Vector3 | undefined
+): GCodeGeometryResult {
   const geometry = new BufferGeometry()
   geometry.setAttribute('position', new BufferAttribute(new Float32Array(positions), 3))
   geometry.setAttribute('color', new BufferAttribute(new Float32Array(colors), 3))
   geometry.computeBoundingBox()
 
-  // Calculate bounding box
   let boundingBox: { min: Vector3; max: Vector3 } | undefined
   if (geometry.boundingBox) {
     boundingBox = {
@@ -155,7 +189,6 @@ export function processGCode(gcode: string | null | undefined): GCodeGeometryRes
       max: geometry.boundingBox.max.clone()
     }
   } else if (positions.length > 0) {
-    // Manual bounding box calculation if computeBoundingBox didn't set it
     let minX = Infinity, minY = Infinity, minZ = Infinity
     let maxX = -Infinity, maxY = -Infinity, maxZ = -Infinity
     for (let i = 0; i < positions.length; i += 3) {
@@ -172,13 +205,127 @@ export function processGCode(gcode: string | null | undefined): GCodeGeometryRes
     }
   }
 
-  const result: GCodeGeometryResult = {
+  return {
     geometry,
     frames,
     boundingBox,
-    firstVertex: initialPosition // Return the toolpath origin (initial position)
+    firstVertex: initialPosition
+  }
+}
+
+/**
+ * Process G-code string synchronously and generate Three.js BufferGeometry.
+ * Results are cached - repeated calls with the same gcode string return the cached result.
+ * Applies vertex decimation to skip near-identical vertices.
+ *
+ * @param gcode - G-code string to process
+ * @returns Geometry data with frames for animation/stepping through the toolpath
+ */
+export function processGCode(gcode: string | null | undefined): GCodeGeometryResult | null {
+  if (!gcode) {
+    return null
   }
 
+  // Return cached result if input hasn't changed
+  if (gcode === _cachedGcodeInput && _cachedGcodeResult) {
+    return _cachedGcodeResult
+  }
+
+  const { toolpath, positions, colors, frames, getInitialPosition } = createDecimatedToolpath()
+
+  // Process G-code synchronously
+  if (toolpath && typeof (toolpath as { loadFromStringSync?: (gcode: string, callback: (line: string) => void) => void }).loadFromStringSync === 'function') {
+    (toolpath as { loadFromStringSync: (gcode: string, callback: (line: string) => void) => void }).loadFromStringSync(gcode, (line: string) => {
+      frames.push({
+        data: line,
+        vertexIndex: Math.floor(positions.length / 3)
+      })
+    })
+  }
+
+  const result = buildGeometryResult(positions, colors, frames, getInitialPosition())
+
+  // Cache the result
+  _cachedGcodeInput = gcode
+  _cachedGcodeResult = result
+
+  return result
+}
+
+// Number of G-code lines to process per chunk before yielding to the UI thread.
+// Larger chunks = less overhead but longer freezes; smaller = smoother UI but slower overall.
+const ASYNC_CHUNK_SIZE = 5000
+
+/**
+ * Process G-code asynchronously in chunks, yielding to the UI thread between
+ * chunks so the loading spinner stays animated and the browser remains responsive.
+ *
+ * Populates the same cache as processGCode, so subsequent sync calls return
+ * the cached result instantly.
+ *
+ * @param gcode - G-code string to process
+ * @param signal - Optional AbortSignal to cancel processing early
+ * @returns Geometry data, or null if cancelled / empty input
+ */
+export async function processGCodeAsync(
+  gcode: string | null | undefined,
+  signal?: AbortSignal
+): Promise<GCodeGeometryResult | null> {
+  if (!gcode) {
+    return null
+  }
+
+  // Return cached result if input hasn't changed
+  if (gcode === _cachedGcodeInput && _cachedGcodeResult) {
+    return _cachedGcodeResult
+  }
+
+  const { toolpath, positions, colors, frames, getInitialPosition } = createDecimatedToolpath()
+
+  if (!toolpath || typeof (toolpath as { loadFromStringSync?: unknown }).loadFromStringSync !== 'function') {
+    return null
+  }
+
+  const typedToolpath = toolpath as { loadFromStringSync: (gcode: string, callback: (line: string) => void) => void }
+
+  // Split into lines and process in chunks
+  const lines = gcode.split('\n')
+  const totalLines = lines.length
+
+  for (let start = 0; start < totalLines; start += ASYNC_CHUNK_SIZE) {
+    // Check for cancellation between chunks
+    if (signal?.aborted) {
+      return null
+    }
+
+    // If the sync path populated the cache while we were yielding, use it
+    if (gcode === _cachedGcodeInput && _cachedGcodeResult) {
+      return _cachedGcodeResult
+    }
+
+    const end = Math.min(start + ASYNC_CHUNK_SIZE, totalLines)
+    const chunk = lines.slice(start, end).join('\n')
+
+    typedToolpath.loadFromStringSync(chunk, (line: string) => {
+      frames.push({
+        data: line,
+        vertexIndex: Math.floor(positions.length / 3)
+      })
+    })
+
+    // Yield to UI thread between chunks (skip yield for the last chunk)
+    if (end < totalLines) {
+      await new Promise<void>(resolve => setTimeout(resolve, 0))
+    }
+  }
+
+  // Final cancellation check
+  if (signal?.aborted) {
+    return null
+  }
+
+  const result = buildGeometryResult(positions, colors, frames, getInitialPosition())
+
   // Cache the result
   _cachedGcodeInput = gcode
   _cachedGcodeResult = result
diff --git a/apps/web/src/routes/Setup/components/VisualizerScene.tsx b/apps/web/src/routes/Setup/components/VisualizerScene.tsx
index aac0b51e8..a11d24595 100644
--- a/apps/web/src/routes/Setup/components/VisualizerScene.tsx
+++ b/apps/web/src/routes/Setup/components/VisualizerScene.tsx
@@ -10,7 +10,7 @@ import { Loader2 } from 'lucide-react'
 import { useGetSettingsQuery, useGetExtensionsQuery } from '@/services/api'
 import { machineToThree, type MachineLimits, type Coordinate } from '@/lib/coordinates'
 import type { HomingCorner } from '@/lib/machineLimits'
-import { processGCode } from '@/lib/gcodeVisualizer'
+import { processGCode, processGCodeAsync } from '@/lib/gcodeVisualizer'
 
 export type VizMode = 'machine' | 'wcs'
 
@@ -622,9 +622,9 @@ export function VisualizerScene({ gcode, limits: _limits, view, viewKey, machine
   const { t } = useTranslation()
   const [webglAvailable, setWebglAvailable] = useState<boolean | null>(null)
 
-  // Deferred gcode loading: show loading indicator in outer DOM, then pass gcode to Canvas
-  // after the browser has painted the overlay. This ensures the spinner is visible before
-  // the heavy processGCode call blocks the main thread inside the Canvas.
+  // Async gcode loading: process gcode in background chunks so the UI stays
+  // responsive, then pass the gcode string to GCodeToolpath once the cache is
+  // populated (so its synchronous useMemo hits the cache instantly).
   const [deferredGcode, setDeferredGcode] = useState<string | null | undefined>(gcode)
   const [isProcessing, setIsProcessing] = useState(false)
 
@@ -635,34 +635,31 @@ export function VisualizerScene({ gcode, limits: _limits, view, viewKey, machine
       return
     }
 
-    // Show loading overlay immediately
+    // Show loading overlay and clear stale geometry while processing
     setIsProcessing(true)
-    setDeferredGcode(null) // Clear stale geometry while loading
-
-    // Double requestAnimationFrame ensures the browser has actually painted
-    // the loading overlay before we let the heavy processGCode run
-    let rafId1 = 0
-    let rafId2 = 0
-    rafId1 = requestAnimationFrame(() => {
-      rafId2 = requestAnimationFrame(() => {
-        // This triggers GCodeToolpath's useMemo which runs processGCode synchronously.
-        // The loading spinner will be visible (though frozen) during the blocking parse.
+    setDeferredGcode(null)
+
+    const abortController = new AbortController()
+
+    // processGCodeAsync processes gcode in chunks, yielding to the UI thread
+    // between chunks so the loading spinner stays animated. When it resolves
+    // the result is cached, so GCodeToolpath's sync processGCode call is instant.
+    processGCodeAsync(gcode, abortController.signal).then(() => {
+      if (!abortController.signal.aborted) {
         setDeferredGcode(gcode)
-      })
+        setIsProcessing(false)
+      }
+    }).catch(() => {
+      if (!abortController.signal.aborted) {
+        setIsProcessing(false)
+      }
     })
+
     return () => {
-      cancelAnimationFrame(rafId1)
-      cancelAnimationFrame(rafId2)
+      abortController.abort()
     }
   }, [gcode])
 
-  // Clear loading state after deferred gcode has been processed and rendered
-  useEffect(() => {
-    if (deferredGcode && isProcessing) {
-      setIsProcessing(false)
-    }
-  }, [deferredGcode]) // eslint-disable-line react-hooks/exhaustive-deps
-
   useEffect(() => {
     if (typeof window === 'undefined') {
       setWebglAvailable(false)