What
The session usage tool now accepts an optional breakdown parameter. When a session is available and a breakdown is requested, it computes and returns a detailed cost and context breakdown alongside the usual usage information.
Why
This lets tools or integrations that query session usage get a more detailed view of where cost and context are being spent, instead of just the summary totals.
Names in the bundlebreakdown
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Added since
A small documentation edit on Create custom subagents touched a line naming breakdown after this was published.
Explore and Plan skip your CLAUDE.md files and the git status snapshot to keep research fast and inexpensive. Every other built-in and [custom subagent](#configure-subagents) loads both, unless its definition sets the [`omitClaudeMd`](#sup…sub-agents see the edit
Confirmed since
Anthropic's documentation has since written up breakdown, on Beta.
Per-iteration token usage breakdown.api/beta see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up breakdown, on Beta.