Surface Codex reasoning tokens and rate limits in Anthropic usage

[sommaht]

Summary

Two small additions to the Codex → Anthropic usage mapping so clients can account for what a Codex turn actually cost.

• Reasoning tokens. parse_codex_usage already reads output_tokens_details.reasoning_tokens into CodexUsage, but map_codex_usage_to_anthropic dropped it. It is now emitted as output_tokens_details.{reasoning_tokens, thinking_tokens}. The second name is what Claude Code records for Anthropic models, so per-turn accounting in its transcripts becomes comparable across providers (verified: Claude Code keeps thinking_tokens in the transcript usage block; before this it was always 0 for Codex models).
• Rate limits. The codex.rate_limits stream event was only converted into a progress ping. Codex sends it before any usage exists, so both translators (buffered reducer and live-stream) keep the latest snapshot and attach it to the CodexUsage built from response.completed. The mapper emits it as a typed codex_rate_limits field (plan_type, limit_reached, primary/secondary used_percent, window_minutes, reset_at) on the terminal message_delta usage. Downstream proxies can log the subscription meter per response; Claude Code itself ignores the unknown key.

Example terminal usage after the change:

{"input_tokens":23,"output_tokens":24,"cache_read_input_tokens":0,"cache_creation_input_tokens":0,
 "output_tokens_details":{"reasoning_tokens":17,"thinking_tokens":17},
 "codex_rate_limits":{"plan_type":"prolite","limit_reached":false,
   "primary":{"used_percent":8.0,"window_minutes":10080,"reset_at":1789765755}}}

Test plan

• cargo test --release: all suites pass; adds a mapper test for reasoning + rate limits, extends the reducer and live-stream codex.rate_limits tests to assert the snapshot reaches the finish usage.
• cargo fmt --check clean.
• Manual: streamed /v1/messages against gpt-5.6-terra at xhigh effort reports 390 reasoning of 566 output tokens; a request through Claude Code shows thinking_tokens populated in the session transcript.

🤖 Generated with Claude Code