Cache Tax for Claude Code

Keep Claude Code's prompt cache warm during breaks.

Cache Tax is a Claude Code mod that refreshes your prompt cache while you step away and shows the estimated rewrite cost before a cold send. Run /keepwarm 90m before a break. Pings cost tokens; choose a window you expect to return within.

Install · Website · How it works · Costs and limits · Commands

A two-line recap in a 330k-token session triggered a $6.61 estimate. After resending, the reported cache write was $6.28. Recorded on 2.1.1; current wording says “up to” the estimated token count. These are API-equivalent costs, not extra subscription charges.

Install

Needs Claude Code 2.1.287 or later, a one-hour cache and Claude Code left running. Mods are on by default. Pings cost tokens, including uncapped output.

claude plugin marketplace add karanb192/claude-code-mods
claude plugin install cache-tax@claude-code-mods

Restart Claude Code or run /reload-plugins in an open session. No early-access flag is needed. If you set CLAUDE_CODE_ENABLE_FUNCTION_HOOKS previously, remove it; current Claude Code ignores it.

In a warm session, run /keepwarm to arm six hours. Use /keepwarm 90m for a shorter window, or /keepwarm off to stop.

Check the main cache lifetime. Included subscription usage defaults to one hour. API-key, usage-credit and cloud-provider sessions default to five minutes, so set promptCacheTtl to "1h" for those billing paths. A 50-minute timer cannot protect a five-minute main cache. See Limits for the fork evidence.

Prefer a settings hook? The hook version warns by default, refuses once with CACHE_TAX_BLOCK=1, and provides a standalone status-line countdown. Warming is part of this mod.

How it works

Before a break: /keepwarm arms a bounded window. After 50 idle minutes, a timer inside Claude Code sends one tool-less fork over the session's transcript. It reads usage after every ping and stops if reads are zero or writes reach 10% of reads. There is no background transcript-polling loop.

When you return cold: for a context of at least 50,000 tokens, the guard drops your ordinary message once when its one-hour clock says cold. It shows the estimated rewrite price. Resend to continue, or /clear and start from a note.

A detected cold write automatically arms at least three hours of keepwarm. /cache-tax shows the current cache estimate, warming window and this session's cold-write tally.

Windows belong to individual sessions. An already-cold session waits for your next turn before pinging. A window ends at its deadline; /keepwarm off also cancels it and clears the always setting.

A recorded warming ping

Sonnet 5, 16 September 2026: the status reported 75k tokens read at $0.02. Nothing appeared in the conversation during the live run. This capture used the one-minute testing interval on 2.0.0; its card's $0.45 rewrite estimate used an older Sonnet price row, versus $0.30 for the same context with the current row. The two-cent ping is a receipt for that session, not a fixed price.