What
- A new "max effort" mode was added: a helper decides when to force maximum effort, gated by a reminder-enabled check before it's applied.
- A status-line reminder ("Max effort · … · /effort to change") is shown when effort is set to max; whether it appears is controlled by the
CLAUDE_CODE_MAX_EFFORT_REMINDERenvironment variable, falling back to a remote flag (tengu_proud_clover, off by default unless enabled server-side). - The VS Code extension's feature-gate table gained the corresponding max-effort reminder gate, wired from
maxEffortReminderEnabled. - The reminder is shown in a warning color rather than a subtle one when the environment variable or flag is set.
- Underneath, the request-building code for side-queries now accepts an
effortoption that becomesoutput_config.efforton the API call; if a model rejects it, Claude Code remembers the model doesn't support it and retries without the field, logging a telemetry event.
Why
This lets you run Claude Code at maximum effort and know at a glance when that mode is active, via /effort to change it, while the underlying request logic gracefully falls back for models that don't support the effort parameter.
Names in the bundleoutput_config.effort
output_config.effort
preserved-thinking modified, high confidence
| Changing top-level `output_config.effort` (restarts the cache, doesn't affect thinking) | A [per-message `output_config`](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#effort-changes) | `mid-conversation-output…see the edit
output_config.effort
mid-conversation-system-messages modified, high confidence
A `role: "system"` message can also carry `output_config.effort` to change the [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level from the next `user` turn on. This is in beta on Claude Fable 5.1, Claude Mythos 5.…see the edit
output_config.effort
preserved-thinking modified, high confidence
| Changing top-level `output_config.effort` (restarts the cache, doesn't affect thinking) | A [per-message `output_config`](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#effort-changes) | `mid-conversation-output…see the edit
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 mid-conversation-system-messages touched a line naming output_config.effort after this was published.
A `role: "system"` message can also carry `output_config.effort` to change the [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level partway through a conversation. This is in beta on Claude Fable 5.1, Claude Mythos …build-with-claude/mid-conversation-system-messages see the edit
Confirmed since
Anthropic's documentation has since written up output_config.effort, on Events.
How hard Claude works on each turn. Sets `output_config.effort` on every Messages call the session makes.api/beta/sessions/events see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
output_config.effort on preserved-thinking