Newton’sNEWTON’S RESEARCH · TOOL COMPATIBILITY
Codex and Claude Code Routing: What Changed by Aug 2026
Codex continues as the software-development workflow inside ChatGPT, with provider configuration still possible through managed profile files; Claude Code routes through `ANTHROPIC_BASE_URL`, but that variable alone does not change billing credentials unless a gateway credential is also active.
What the evidence establishes
Evidence is separated from inference and hypothesis so the conclusion can be challenged without changing the facts.
OpenAI documents Codex as an AI agent dedicated to coding tasks and includes it in the ChatGPT workflow.
OpenAI’s Codex docs and ecosystem documentation indicate custom providers are configured through model-provider config and use the Responses API when `wire_api = "responses"`.
Anthropic’s Claude Code LLM gateway guide states that `ANTHROPIC_BASE_URL` points Claude Code at a gateway, and requires credential precedence to move off native authentication.
Anthropic support guidance still warns against leaving `ANTHROPIC_API_KEY` active when using subscription billing.
If builders need lowest-friction continuity, Codex and Claude Code still matter most in our onboarding funnel. The key is to avoid promising full support where we only have configuration guidance or partial verification.
Codex truth line (as of Aug 29, 2026)
- Treat Codex as the verified-first path only when the profile is using OpenAI-compatible `Responses` wire format.
- Keep setup in profile-managed space (`~/.codex/config.toml` and `.env`) and avoid manual shell-only overrides.
- Use a non-sensitive repo task before broad rollout: list models, run a tiny edit, and confirm route identity and billing output.
Claude Code truth line (as of Aug 29, 2026)
Claude Code can be configured for LLM gateway usage, but gateway status is not automatic. `ANTHROPIC_BASE_URL` points traffic at a gateway endpoint; billing/auth still follows active subscription state unless one gateway credential is intentionally in use.
- Collect `/status` and environment checks before declaring production use. The docs require an active gateway auth line in status before trust.
- Unify model aliases/discovery so session startup sees reachable Newton’s model IDs.
- Treat this as assisted integration until end-to-end receipts and tool-call behavior are reproduced in real workflows.
The strategic choice is not broad support theater. It is reducing migration anxiety by giving builders one proven path for Codex and one explicit assisted path for Claude Code, each with rollback instructions.
Apply this to your workload.
Compare the available options using the same workload, model requirements, price, delay, and data constraints.