Update docs for hot/cold storage pricing

- Split storage into hot ($0.50/GB-month) and cold ($0.02/GB-month) tiers
- Hot storage: local NVMe cache, sampled every few seconds while active
- Cold storage: object storage, measured hourly, charged 24/7
- Updated PricingRates component to show both tiers
- Updated billing FAQ to clarify hibernation charges

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: Claude Code

src/components/react/PricingRates.tsx

@@ -4,7 +4,8 @@ import { Switch } from '@/components/ui/switch';
 export const HOURLY_RATES = {
   cpu: 0.07,
   ram: 0.04375,
-  storage: 0.5,
+  storageHot: 0.5,
+  storageCold: 0.02,
 };
 
 export function PricingRates() {
@@ -53,16 +54,21 @@ export function PricingRates() {
           unit={perSecond ? '/GB-second' : '/GB-hour'}
         />
         <RateCard
-          title="Storage"
-          rate={`$${HOURLY_RATES.storage.toFixed(2)}`}
+          title="Hot Storage"
+          rate={`$${HOURLY_RATES.storageHot.toFixed(2)}`}
           unit="/GB-month"
-          description="Prorated to the hour. Storage is aggregated across all Sprites."
+          description="Local NVMe cache for active working data, sampled every few seconds."
+        />
+        <RateCard
+          title="Cold Storage"
+          rate={`$${HOURLY_RATES.storageCold.toFixed(2)}`}
+          unit="/GB-month"
+          description="Object storage for persistent data, measured hourly."
         />
       </div>
 
       <p className="text-xs text-[var(--sl-color-gray-2)] pt-2 border-t border-[var(--sl-color-hairline)]">
-        All compute resources are billed per second. Storage is billed hourly
-        but aggregated monthly.
+        All compute resources are billed per second. Hot storage is sampled every few seconds while active; cold storage is measured hourly.
       </p>
     </div>
   );

src/content/docs/reference/billing.mdx

@@ -56,26 +56,39 @@ Compute is billed **per-second** with no minimum. If you run a command for 30 se
 
 ## Storage Billing
 
-### How It Works
+Sprites use a two-tier storage system: **hot storage** for active working data and **cold storage** for persistent object storage.
+
+### Hot Storage
+
+Hot storage is the local NVMe cache used by the filesystem (JuiceFS) for active working data.
+
+- **Sampled every few seconds** while your Sprite is active
+- **Only charged while running**: No hot storage charges when hibernated
+- **Automatically managed**: The filesystem handles caching transparently
+
+Hot storage represents the working set of data actively being used during your session.
+
+### Cold Storage
 
-Storage is billed monthly based on the actual data stored on your Sprite's filesystem:
+Cold storage is the object storage bucket where all your Sprite's persistent data lives.
 
+- **Measured hourly** by summing the actual size of all objects in your bucket
+- **Always charged**: Cold storage accrues 24/7, even when hibernated
 - **TRIM-friendly**: You only pay for data actually written
 - **Deleted files reduce cost**: Deleting files reduces your storage bill
-- **Compression**: Data is compressed in storage
 
 ### Starting Allocation
 
 Every Sprite includes 100 GB of storage capacity. Storage does not autoscale yet.
 
 ### Typical Usage
 
-| Environment | Storage | Within Plan? |
-|------------|---------|--------------|
-| Minimal (OS + tools) | ~2 GB | Yes |
-| Dev environment | ~5 GB | Yes |
-| With datasets | ~10 GB | Yes |
-| Large datasets | ~60 GB | +10 GB overage |
+| Environment | Hot Storage (active) | Cold Storage | Within Plan? |
+|------------|---------------------|--------------|--------------|
+| Minimal (OS + tools) | ~1 GB | ~2 GB | Yes |
+| Dev environment | ~2 GB | ~5 GB | Yes |
+| With datasets | ~3 GB | ~10 GB | Yes |
+| Large datasets | ~5 GB | ~60 GB | +10 GB overage |
 
 ## Cost Optimization
 
@@ -136,10 +149,10 @@ Usage and billing information is available through your Fly.io dashboard and org
 > Compute billing starts when you execute a command and stops when the command completes or the Sprite hibernates.
 
 **Do I pay while hibernated?**
-> No compute charges while hibernated. You only pay for storage.
+> No compute or hot storage charges while hibernated. You only pay for cold storage (object storage), which accrues 24/7.
 
 **How is storage measured?**
-> Storage is measured based on actual data on disk, not allocated capacity. It's sampled periodically throughout the month.
+> Hot storage (NVMe cache) is sampled every few seconds while your Sprite is active. Cold storage (object storage) is measured hourly based on actual data stored, not allocated capacity.
 
 **Are checkpoints billed?**
 > Yes, checkpoints count toward your storage usage.