codex-subagent-router/skills/codex-subagent-router/references/platforms.md

Runtime and Configuration

Use this reference for actual host/configuration diagnosis. This is not a prerequisite checklist for every task.

Separate four kinds of evidence

1. Official model documentation: product and API capabilities.
2. Local configuration: requested defaults, providers and role bindings.
3. Current child-tool schema: what this session accepts.
4. Tool results: what was created, observed, completed or interrupted.

Do not substitute one for another. A model available in an API or the task picker may be absent from child tools. A CLI success does not verify a Desktop child path.

Inspect only relevant configuration fields; never dump environment blocks, credential files or HTTP authorization headers. Resolve CODEX_HOME from the environment, falling back to the user's .codex directory; do not overwrite that environment variable.

Optional Codex defaults

For clients that support the documented keys, an example is:

# Example only; merge intentionally into the existing configuration.
model = "gpt-6.1-sol"
model_reasoning_effort = "medium"

[agents]
default_subagent_model = "gpt-6.1-sol"
default_subagent_reasoning_effort = "medium"
max_concurrent_threads_per_session = 3

This is not an automatic router, permission grant or universal host configuration. Never overwrite an existing config to install this example. Preserve user model/provider choices and verify the actual client accepts the keys. Per-agent configuration and host overrides may change resolution.

The Sol default assumes GPT-6.1 Sol is exposed and suits mixed engineering work. Resolve parent and child availability separately: a model in the picker does not prove child support. Explicitly route bounded tasks to GPT-6 Luna where supported; do not make Luna a universal fallback for arbitrary inherited work. If 6.1 is unavailable, use the compatibility routes. A fixed sol_* or luna_* role may still bind an older model: inspect the binding, then use an overridable role if available and appropriate. Do not rename or claim to upgrade a fixed role through prompt text.

For an authorized migration, preserve a supported effective effort. GPT-6.1 Sol's API accepts low/medium/high/xhigh/max and rejects none/minimal; use low as an initial replacement for those settings and check representative work. Tool calling requires Responses; its Chat Completions support is without tools. Desktop/CLI controls, including Ultra, must be checked separately against the actual host; do not copy them into API requests. Installation does not apply any of these configuration changes.

The official Codex configuration describes the child-thread limit as excluding the parent. A collaboration tool may expose a different active-slot count including the parent. Use that live tool's counting and release semantics; do not copy either number blindly.

When selecting a route, explicitly request model and effort with a compatible fork mode if supported. Check omitted-setting inheritance, custom-agent bindings and override restrictions. A prompt cannot implement an unsupported model switch.

Native Responses Multi-agent beta is a separate mechanism: children share the request model and tools, and its active-descendant limit excludes root. Codex host schemas may expose per-child model overrides and different slot semantics. Select the actual mechanism first; do not put API beta fields into Codex TOML or promise cross-model native children. See Sol 6.1 adaptation for beta opt-in, history handling and incompatible request options.

Diagnosis and safe fallbacks

Resolve the executable actually used by the relevant client, inspect its help/schema and record its version when needed. Do not prescribe speculative CLI flags or launch model calls merely to print a marker. Use an authorized real task to verify child execution.

Missing role/sandbox/timeout fields mean working role, read-only scope and deadlines are contract limits only. Keep requested and observed identity distinct. A completed task with unknown model identity can be accepted for its output, but cannot satisfy an explicit identity-verification gate.

No close tool: retain the truthful idle/completed/interrupted state and follow the host's actual capacity behavior. No child tools: continue locally; do not launch another user-owned task or nested CLI as an unapproved substitute.

Configuration changes may require a fresh session or explicit reload. Writing a file is not evidence that the current session adopted it.

Sources

Checked 2026-09-14: Codex subagents, OpenAI model catalog. Recheck changed product/API facts before altering real configuration.

Model recommendation and migration checked 2026-10-06: Codex models, GPT-6.1 Sol, migration guidance. Configuration keys above retain their original reference date; the current client schema takes precedence.