Codex provider

The Codex telemetry provider reads ~/.codex/sessions/ rollout files and surfaces them via AgentTelemetry. The rollout format is actually simpler than Claude's transcript: every event is a tagged union with a known type, and the model's context-window size is written directly into each token_count event — no per-model lookup table needed for the context fraction.

Data sources

CODEX_HOME lets users point Codex at a non-default state directory; the provider reads it once per PID and caches the result.

PID correlation

Filenames are unreliable for correlation. Codex writes timestamps in the host's local time, not UTC. On a UTC-3 machine a session that started at 13:43:38Z produces a filename with 10-43-38 — naive UTC parsing would match nothing.

The provider correlates by opening each candidate rollout file and reading the authoritative UTC timestamp from its first session_meta event's payload.timestamp. Matches within ±90 s of the process's start time.

What we extract

From each event_msg.payload where type == "token_count" (the latest populated info wins):

• total_token_usage.{input_tokens, cached_input_tokens, output_tokens, reasoning_output_tokens} — session cumulative
• last_token_usage.input_tokens — the live context signal (cumulative total_tokens grows unbounded across turns and would report >100% on any long session)
• model_context_window

From each response_item.payload:

• function_call / custom_tool_call events increment the unresolved call-id set
• function_call_output / custom_tool_call_output clear it
• If the last response item is an unresolved call, pending_tool gets its name

From each turn_context.payload:

• model (e.g. gpt-5.4, gpt-5-codex)

Pricing

Hardcoded in src/telemetry/codex/pricing.rs with a CODEX_PRICING_AUDITED_AT constant. Rates are estimates aligned with public OpenAI pricing tiers; every cost surfaces with cost_is_estimated: true.

The table covers gpt-5*, gpt-5-codex, and o3/o4 reasoning families. Reasoning output tokens are billed at the output rate.

Fields Codex leaves null

Schema stability

The rollout format is internal to Codex. The parser ignores unknown event types via a #[serde(other)] catchall. If a future Codex release changes the schema, telemetry falls back to null until we audit. See Stability and compatibility for the audit cadence.