No overridable default effort level: settings effortLevel is rewritten by /effort, CLAUDE_CODE_EFFORT_LEVEL hard-locks it

Summary

There is no way to pin a default effort level for new sessions that /effort can still override in-session. The two candidate mechanisms each fail in the opposite direction, and neither matches how the model equivalent works:

• effortLevel in ~/.claude/settings.json is too soft: /effort and /model write back into that same file, so it cannot act as a pin.
• CLAUDE_CODE_EFFORT_LEVEL is too hard: it overrides --effort and /effort, so exporting it disables in-session effort changes entirely.

Model configuration has both halves — ANTHROPIC_MODEL (overrides the model setting, still changeable with /model) and ANTHROPIC_DEFAULT_MODEL (applies only when no file sets model). Effort has only the hard-locking form.

Detail

1. The settings key cannot serve as a pin, because in-session commands rewrite it.

With "effortLevel": "high" set in ~/.claude/settings.json, using /effort adds a per-model entry:

{
  "effortLevel": "high",
  "modelSettings": {
    "claude-opus-5": { "effortLevel": "low" }
  }
}

Per the settings docs, modelSettings is resolved one model at a time together with effortLevel, so the more specific per-model entry then wins over the top-level key on every subsequent session. The user's intended default is silently superseded by a value written as a side effect of a transient in-session command. (This is the effort-level analogue of #63413, which reports the same write-back behavior for /model.)

2. The env var name does not follow the model convention, and the wrong guess fails silently.

The model variable is ANTHROPIC_MODEL; the effort variable is CLAUDE_CODE_EFFORT_LEVEL. Guessing ANTHROPIC_EFFORT by analogy produces no warning and no effect — an export that appears correct does nothing, with no diagnostic anywhere.

3. Precedence is inverted relative to the model variable.

From the environment variables reference:

--model and /model override ANTHROPIC_MODEL, while CLAUDE_CODE_EFFORT_LEVEL overrides --effort and /effort.

So the model variable sets a default the user can still move, while the effort variable is an absolute lock. (#90419 reports the user-facing symptom of this — in-session effort changes silently not applying when the variable is exported.)

Expected behavior

An effort equivalent of ANTHROPIC_DEFAULT_MODEL — for example ANTHROPIC_DEFAULT_EFFORT or CLAUDE_CODE_DEFAULT_EFFORT_LEVEL — that seeds new sessions and is still overridable by --effort and /effort. Alternatively, a settings scope for effortLevel that in-session commands do not write back into, so a file-based pin is possible.

Steps to reproduce

1. Set "effortLevel": "high" in ~/.claude/settings.json.
2. Start a session, run /effort, pick a different level.
3. Inspect ~/.claude/settings.json — a modelSettings.<model>.effortLevel entry now exists and outranks the top-level key for every later session on that model.
4. Separately, export ANTHROPIC_EFFORT=medium — no effect, no warning.
5. export CLAUDE_CODE_EFFORT_LEVEL=high — applies, but /effort is now inert for the session.

Related issues

• #90419 — in-session effort changes not persisting when CLAUDE_CODE_EFFORT_LEVEL is set (symptom of point 3)
• #63413 — session-only flag for typed /model (same write-back-as-side-effect problem, model side)
• #95347 — effortLevel has no session-scoped write channel
• #82114 — per-model default effort levels (closed as not planned; modelSettings now provides this, which is what makes point 1 reachable)

Environment

• Claude Code 2.1.241

Docs referenced

• https://code.claude.com/docs/en/env-vars (Precedence; CLAUDE_CODE_EFFORT_LEVEL row)
• https://code.claude.com/docs/en/settings (effortLevel / modelSettings resolution)