Subagent budget of 30,000 tokens (new in 2.1.291) is not configurable and not documented

What changed

Starting with Claude Code 2.1.291, the Agent tool description shown to the main session contains:

Each agent you launch has a budget of 30,000 tokens. The budget does not count the context the agent starts with: its system prompt, its tools, and your prompt to it.

The string is present in the 2.1.291 binary and absent from 2.1.289 and 2.1.287 (checked with grep -a "has a budget of" on the installed version binaries). I could not find it mentioned in the CHANGELOG entries for 2.1.290 / 2.1.291.

Problem

• I found no way to change the budget: nothing in the settings reference, no environment variable, no frontmatter field in the subagent docs (.claude/agents/*.md).
• 30,000 tokens is too small for subagents that have to read project material before they can work (skills, conventions, several source files). In my setup a coding subagent needs most of that budget just for required reading.
• Observed in one session on 2.1.291: a web-research subagent returned at 29,788 tokens and reported that it had only covered part of the requested search scope. Another subagent in the same session reported 55,626 tokens and completed, so it is also unclear whether the budget is enforced or only advisory.
• The main session adapts to the stated budget (smaller briefs, doing work itself instead of delegating), which changes behaviour for workflows built around delegation.

Expected

• A way to configure the per-agent budget: a settings key and/or environment variable, ideally also a per-agent frontmatter field, including an option to disable it.
• Documentation of the budget: what counts toward it, whether it is hard-enforced, and what happens when an agent reaches it.
• A changelog entry for the change.

Workaround

Pinned to 2.1.289 with DISABLE_AUTOUPDATER=1.

Environment

• Claude Code 2.1.291 (native install), macOS (Darwin 25.6.0)
• Custom subagents defined in ~/.claude/agents/