Slash-command settings should be session-scoped by default

What version of Codex are you using?

Codex CLI 0.148.0

What platform is your computer?

macOS arm64

What issue are you seeing?

Manual slash-command settings are unexpectedly sticky across unrelated sessions.

I used /fast as a one-off change for the current thread. Codex wrote service_tier = "fast" to ~/.codex/config.toml, so later fresh Codex processes and unrelated agents inherited the accelerated tier even though their launch commands did not request it.

The broader problem is not limited to /fast: most or all interactive slash-command selectors—such as model, reasoning effort, personality, and service tier—should be scoped to the current thread/session by default. A manual experiment in one conversation should not silently change defaults for future conversations.

What steps can reproduce the bug?

1. Start Codex without an explicit service-tier override.
2. Use /fast, intending it as a one-off current-thread change.
3. Observe that ~/.codex/config.toml gains service_tier = "fast".
4. Start a fresh, unrelated Codex process without a service-tier argument.
5. Observe that the new process inherits Fast.

What is the expected behavior?

Slash-command changes should affect only the current thread/session by default.

Persisting a choice for future sessions should require a separate, explicit action such as Make default, or a clearly labeled confirmation. The UI should distinguish:

• the effective value for the current thread;
• the configured default for future threads; and
• whether the current action will mutate persistent configuration.

This should apply consistently to /fast, /model, reasoning-effort, personality, and similar interactive selectors unless a setting is inherently global and clearly presented as such.

Why this matters

The current behavior makes one-off experimentation unsafe and can unintentionally change cost, latency, or behavior across unrelated agents and workstreams.

A command-line override such as -c service_tier=default is a workaround, but callers should not need to defensively override a persistent mutation they never intentionally made.

Additional information

Feedback was also submitted through /feedback without logs. Feedback thread ID: 01a01bb2-7780-7232-ba37-8d749e19ec8b.

Start by tracing how interactive slash-command selectors update the current thread and how those changes are written to ~/.codex/config.toml. Compare /fast with model, reasoning-effort, and personality handling, then determine how session values and persistent defaults should be separated. Done means one-off changes no longer affect unrelated future sessions and explicit default changes remain distinguishable.