My Claude Code week started ending on Wednesday. I blamed the September 14 cut, like everyone on r/ClaudeAI did. Then I opened the usage screen and the biggest line was not me typing. It was the helpers I had told it to launch.
So I read a month of my own logs before touching a single setting. 455 sessions, 63,000 requests, and a number next to every saving tip I had been told to apply.
Which of the five fixes everyone lists gives a measurable share of the week back, and which one costs quality?
Claude Code writes one JSONL file per session under ~/.claude/projects/, and one file per subagent run next to it. Every assistant line carries the usage of its request: input, output, cache reads, cache writes.
The first trap is double counting. The log writes the same answer about twice (1.96 lines per request in my month), so summing every line gave 18.6 billion tokens. De-duplicated on message id and request id, it was 9.3 billion. Every number below is the de-duplicated one.
The second limit is bigger. Anthropic publishes the weekly limit as percentages and plan multipliers, never as a token count. So everything here is tokens from one workload, not a share of your week. The order may change for you. The usage screen will tell you.
The cut itself is simple arithmetic. Call the old weekly limit 100. The summer promotion made it 150. The permanent level since September 14 is 125. From 150 to 125 is the 17% people feel, and Anthropic's "+25%" is true at the same time.
2,631 subagent runs in the month. They took 48.1% of all tokens and wrote 64% of all output, which is the heaviest line on the meter.
Each one pays an entry price. Before a subagent does anything, its opening request already carries a median of 47,117 tokens: the instructions, the tool list, the skill list, all sent again. Someone else measured 16 to 21k on a different machine with tiny agent prompts, and their line stuck with me: your agent file is a rounding error inside its own launch cost.
The model is the other half. A subagent inherits the main session's model unless the agent file says otherwise. Switch to the biggest model for yourself and every helper runs on it. In my logs the smallest model handled under 1% of subagent requests.
Two habits, then. Skip the subagent for a job you could do in place. Pin a small model on the ones you keep. Nobody has measured what pinning saves as a share of the week, and a small model that needs more turns can cost more, so this stays a habit with a direction rather than a percentage.
The main session's prompt cache lives one hour on a subscription. A subagent's lives five minutes. My logs agree with the docs on this: every cache write from a subagent landed on the 5-minute tier, every write from a main session on the 1-hour tier.
A Reddit user whose subagents wait on long builds saw cache writes go from 12 million tokens to 3 million after the change. In my own logs it barely matters: 2 requests in 1,000 arrived after a wait of five minutes, though each one rewrote about 75,000 tokens. If your subagents idle, turn it on. If they run in short bursts, leave it, because an hour of cache costs more to write.
This is the one I did not expect. A message sent within five minutes of the previous one wrote about 1,200 tokens of cache. After a pause of more than an hour, the median was 130,332. The session at that moment held about 175,000 tokens, so most of it was written again.
Two cheap habits. Clear the session when a task is done, while the cache is still warm, so the next task starts small. And when Claude Code offers to resume a big session from a summary after a break, take it. A model switch mid-session empties the cache too, since each model keeps its own.
The caveat: 79 cold returns is a small sample, and some of them follow a compaction rather than pure idle.
One developer ran the same 29 real tasks at all five effort levels. Mean cost per task went from $2.50 at low to $8.84 at max. Medium passed 28 of 29, more than any level above it. His words: the curve appears to peak at medium.
Then the catch. On the hard problems he picked, low passed 0 of 5 and high passed 5 of 5. A low attempt took two minutes, a high one thirty-three. So medium to build, high when a mistake is expensive, max almost never. Those costs are in dollars on an older model, not a share of your week.