I've been leaning on Claude Code hard for a few weeks, with long sessions and lots of sub-agents. I wanted to know where the money actually goes, so I priced every call in my logs at list price. 954 of my 7,802 calls sent more than 400k tokens of context. Those 12% of calls cost 31% of the total.

What I counted

Claude Code keeps a .jsonl file per session under ~/.claude/projects. Each API call is logged with its token counts: input, cache writes, cache reads and output. The same message can show up on several lines, so I counted each message id once.

I took a call's context to be input plus cache reads plus cache writes. Then I priced everything at Anthropic's list prices as of 26 Oct. Opus 5.5 is $4 in and $20 out per million tokens, with cache reads at $0.20. I'm on a plan, so treat these as API-equivalent figures.

The result 

band calls % calls cost % cost <100k 2787 35.7% $114.83 20.3% 100-200k 2898 37.1% $174.04 30.8% 200-400k 1163 14.9% $101.71 18.0% 400k+ 954 12.2% $174.78 30.9%

That's $565 across all the logs. Sub-agents were $289 of it, a bit over half. Output tokens barely matter. Nearly all the cost is context being sent again and again.

Every call re-sends the whole conversation. Cache reads are cheap per token, but at 400k tokens a call even the cheap rate adds up. A session that runs past a few hundred thousand tokens pays that price on every turn after.

The other thing I noticed was limits. I hit the 5-hour limit on 14 separate occasions in about two weeks. In the 5 hours before each one I'd used between roughly $19 and $43 of list-price usage. That spread is too wide to say anything about the limit from my logs alone.

What I'd try, though I haven't tested it: clear the session when a task is done instead of carrying on. Start the next task from a short summary. Use a cheaper model for sub-agents that only read and search. I haven't measured whether any of that saves money yet.

Run it on your own logs

I put the script on GitHub: ctxtax. It's one Python file with no packages to install, and it only reads local files. It prints numbers, never message text.

curl -O https://raw.githubusercontent.com/TrueHorison/ctxtax/main/ctxtax.py python ctxtax.py

A few limits. It's three weeks of my kind of work. List prices aren't what subscribers pay. The 400k cut-off is my choice. And it only reads Claude Code logs.

The thing I can't work out alone

The usage-limit threads are full of "my limit feels smaller" with no way to compare. python ctxtax.py --meter prints one line per limit hit: the day, the usage in the 5 hours before it, and the model mix. It prints numbers only. If a few people paste theirs in the comments, we'd have a record we can actually compare.

What share of your cost comes from the 400k+ calls?

Written with AI help.