Cache Money

Keep the Anthropic prompt cache warm during Claude Code sessions — especially during peak hours when usage limits are tighter — by scheduling lightweight pings tuned to your cache TTL.

Why This Matters

Claude Code sends the full conversation context with every API call. Anthropic caches this prefix server-side and serves subsequent calls from cache at ~10% of the base input price. But the cache expires after a TTL period of inactivity:

TTL Tier	Duration	Cache Write Cost	Who Gets It
Default	5 minutes	1.25x base input	All plans (no ttl field specified)
Extended	1 hour	2x base input	Max-tier plans (server-side in Claude Code), or explicit ttl: "1h" via API

Cache reads cost 0.1x base input regardless of TTL tier — that's the 90% saving.

If a session sits idle past its TTL, the next call pays full cache-write price for the entire context — up to 1M tokens. During peak hours (weekdays 5:00 AM – 11:00 AM PT), Anthropic's rolling session limits are consumed faster, making every cache miss doubly expensive: higher rebuild cost plus faster quota burn.

For detailed technical background, consult references/cache-mechanics.md.

Workflow

Step 1: Assess Timing

Determine the current time and day of week in Pacific Time (PT) using:

TZ=America/Los_Angeles date "+%A %H:%M PT"

Classify the current window:

Condition	Status
Weekday, 5:00 AM – 11:00 AM PT	Peak hours active — cache warming strongly recommended
Weekday, 4:47 AM – 4:59 AM PT	Peak approaching — pre-warming recommended
Weekend or outside peak	Off-peak — cache warming optional, still saves on idle sessions longer than the TTL

Report the status to the user in one line before proceeding.

Step 2: Detect Cache TTL

Determine which TTL tier is active. Ask the user:

Are you on a Max-tier plan (which enables 1-hour cache TTL in Claude Code), or the default (5-minute cache TTL)?

Use the answer to set the ping interval:

TTL Tier	Cache Duration	Ping Interval	Safety Margin
Extended (1h)	60 minutes	55 minutes	5 minutes
Default (5min)	5 minutes	4 minutes	1 minute

If the user is unsure, default to the 5-minute TTL (4-minute ping interval) — it's safe for all plans and the overhead is minimal.

Step 3: Start the Cache Ping Loop

Invoke the /loop skill to schedule the recurring ping at the determined interval:

For 1-hour TTL (Max-tier):

Skill tool: skill="loop", args="55m Cache ping. Reply with only: ok"

For 5-minute TTL (default):

Skill tool: skill="loop", args="4m Cache ping. Reply with only: ok"

Each ping triggers one lightweight API call that renews the cached prompt prefix. The response is minimal — just "ok" — so token consumption per ping is negligible.

Step 4: Confirm to User

After starting the loop, report:

1. TTL tier: Which cache duration was detected (5-min or 1-hour)
2. Interval: The chosen ping interval and why
3. Peak window: Whether currently in peak hours
4. How to stop: End the session or cancel the loop
5. Savings: Cached tokens cost ~90% less than uncached — on a large context this adds up fast

Timing Reference

Timezone	Peak Start	Peak End
PT (Pacific)	5:00 AM	11:00 AM
MT (Mountain)	6:00 AM	12:00 PM
CT (Central)	7:00 AM	1:00 PM
ET (Eastern)	8:00 AM	2:00 PM
GMT / UTC	1:00 PM	7:00 PM
CET (Central Europe)	2:00 PM	8:00 PM
IST (India)	6:30 PM	12:30 AM
JST (Japan)	10:00 PM	4:00 AM (+1)
AEST (Sydney)	11:00 PM	5:00 AM (+1)

Important Notes

• The cache is per-session. Each active Claude Code conversation has its own cached prefix. The ping must happen within the same session to renew it.
• The ping only works while the session is open. Closing the terminal or ending the session invalidates the cache regardless of the loop.
• Off-peak sessions still benefit if idle periods exceed the TTL — the cache expires based on inactivity, not time of day.
• The first API call after cache expiry is always a full-price write. Every subsequent call within the TTL is a cache read at ~10% cost.