Claude Code vs Codex CLI in 2026: An Honest Head-to-Head

TL;DR: Claude Code and Codex CLI are the two leading agentic coding CLIs, and the real difference is the wire protocol, not the vibes. Claude Code speaks Anthropic's Messages API and is configured with ANTHROPIC_BASE_URL + ANTHROPIC_API_KEY. Codex CLI (0.130+) speaks only OpenAI's Responses API, configured in ~/.codex/config.toml and reading OPENAI_API_KEY. The punchline in this claude code vs codex cli comparison: you don't have to pick one. Because llmapi.pro exposes both protocols on the same base URL with the same key and the same models, you can run both CLIs side by side off one sk-relay-... key.

Claude Code vs Codex CLI: the core difference is the protocol

Both tools do the same job — an agent in your terminal that reads your repo, edits files, runs commands, and iterates. Where they diverge is how they talk to a model endpoint, and that decides what you configure.

	Claude Code	Codex CLI
Protocol	Anthropic Messages	OpenAI Responses (wire_api = responses)
Config surface	Env vars	~/.codex/config.toml
Base URL var	ANTHROPIC_BASE_URL	base_url in provider block
Key var	ANTHROPIC_API_KEY	OPENAI_API_KEY
Model select	claude --model <id> or /model <id>	model in config / provider block

A detail that bites people: Codex CLI 0.130+ removed the old chat/completions wire format. It now only supports the Responses API, so a provider block has to set wire_api = responses. If you're following a tutorial that points Codex at a /chat/completions URL, it's out of date. We covered that change in depth in OpenAI protocol and Codex CLI support is live.

Workflow: how each one feels day to day

Claude Code leans into a conversational loop. You launch it, it plans, and you steer with natural language and slash commands. Switching models mid-task is a first-class move:

# pick a model at launch
claude --model claude-opus-4-8

# or switch in-session
/model claude-sonnet-4-6

That in-session /model switch is handy when you want a heavier model for a gnarly refactor and a lighter one for routine edits, without restarting your session.

Codex CLI is more config-forward. Your provider, model, and wire format live in a TOML file, so once it's set the behavior is stable and reproducible across runs. That's a genuine strength for scripted or CI-adjacent use, where you want the same configuration every time and no surprise prompts about which model is active.

Neither workflow is objectively better. Terminal-first developers who like to keep a long, exploratory session usually settle into Claude Code; those who want a pinned, declarative setup tend to prefer Codex. The good news is that the choice no longer locks you to one vendor's models.

The punchline: you don't have to choose

The reason this is a real "both" and not a forced one: llmapi.pro exposes both protocols on the same base URL, with the same key and the same models.

• https://llmapi.pro/v1/messages — Anthropic Messages (what Claude Code wants)
• https://llmapi.pro/v1/chat/completions and https://llmapi.pro/v1/responses — OpenAI (what Codex wants)

Same sk-relay-... key (get one at /register), same model catalog — claude-opus-4-8, claude-sonnet-4-6, and the rest from GET /v1/models. So you can drive both CLIs against the same account.

Claude Code setup

Two env vars and you're running:

export ANTHROPIC_BASE_URL=https://llmapi.pro
export ANTHROPIC_API_KEY=sk-relay-your-key

claude --model claude-opus-4-8

Full walkthrough, including persisting the env vars and verifying the connection, is in the Claude Code API key setup guide.

Codex CLI setup

Codex reads ~/.codex/config.toml. Define a provider block that points at the /v1 root and selects the Responses wire format:

model = "claude-opus-4-8"
model_provider = "llmapi"

[model_providers.llmapi]
name = "llmapi.pro"
base_url = "https://llmapi.pro/v1"
wire_api = "responses"

Then give Codex the key via the variable it reads:

export OPENAI_API_KEY=sk-relay-your-key
codex

Two things worth calling out:

1. base_url is the /v1 root, not a full endpoint path. Setting wire_api = "responses" is what selects the OpenAI Responses endpoint for you.
2. Codex reads OPENAI_API_KEY for the key value, even though the key is your sk-relay-... key. The variable name is OpenAI's; the value is yours.

If you also use VS Code-based agents, the same one-key idea covers them — see Cline & Roo Code with a Claude-compatible API.

Which one should you actually use?

A short, honest decision guide:

• Long, exploratory sessions with frequent model switching → Claude Code. The in-session /model command and conversational loop fit that rhythm.
• Pinned, declarative, reproducible setup → Codex CLI. Everything lives in config.toml, which is easy to commit and share with a team.
• You can't decide, or different teammates prefer different tools → run both off one key. There's no extra account to manage.

The catch

Be clear-eyed about what a relay is: a third party between your CLI and the model. That has real implications.

• It's another hop in your network path. If your own connection or proxy is flaky, both CLIs feel it. When something stalls, check the exact error text and HTTP status your terminal prints before assuming the worst.
• You're trusting the relay with your requests. That's a deliberate trade for a single key, both protocols, and a shared model catalog. If your policy forbids routing code through a third party, that trade isn't for you — and that's a legitimate reason not to use any relay.
• Version drift is real. Codex's removal of the chat/completions wire format is exactly the kind of breaking change to watch. Pin your CLI versions if reproducibility matters.

For most terminal-first developers the win is simple: stop maintaining two vendor accounts and two billing relationships to evaluate two tools. Point both at https://llmapi.pro/v1, use one sk-relay-... key, and let the CLI you prefer win on its own merits.

llmapi.pro is an independent, Claude-compatible API relay; we are not affiliated with Anthropic. Claude Code, Codex CLI, and OpenAI are used for identification only.