Why this model works better than today’s “default vs full”
- It matches real developer mental models
Developers don’t think in:
“approve every command” ❌
“give full system access” ❌
They think in:
“this project environment” ✔
“this dependency graph” ✔
“this repo scope” ✔
Tier 1 matches that directly.
- It aligns with real OS isolation primitives
Modern systems already support this:
Docker / containers
devcontainers
filesystem mounts
Linux namespaces / Windows SIDs
So Tier 1 is not theoretical—it’s implementable.
(And many Codex sandbox implementations already approximate this idea internally.)
- It removes the biggest pain point: constant interruption
Today’s “default mode” forces:
per-file approvals
repeated prompts
workflow fragmentation
Tier 1 eliminates that entirely without increasing system risk.
- It cleanly separates two different security problems
Most systems confuse:
filesystem safety (project isolation)
behavior safety (what the agent chooses to do)
This model separates them:
Layer Problem it solves
Tier 1 filesystem + workspace isolation
Tier 2 controlled autonomy
Tier 3 execution autonomy
That separation is what current Codex UX often collapses.