Use Codex and Claude Code

mistral.rs can back coding-agent clients through the compatibility APIs those clients already speak.

Client	API surface	Base URL to configure
Codex	OpenAI Responses	`http://localhost:1234/v1`
Claude Code	Anthropic Messages	`http://localhost:1234`

Use default for a single-model server. With multi-model serving, use a model id exactly as it appears in GET /v1/models.

Start mistral.rs

Start a model that is tuned for tool use and code:

mistralrs serve -p 1234 -m Qwen/Qwen3-Coder-Next

Check that the server is reachable:

curl http://localhost:1234/v1/models

For Codex and Claude Code, let the coding agent own normal file edits, shell commands, and repository inspection. Enable mistral.rs server-side agent tools only when you deliberately want web search or Python code execution to happen inside the mistral.rs server as well.

Codex

Codex uses the OpenAI Responses wire API for custom providers. Put provider configuration in your user-level ~/.codex/config.toml; Codex ignores provider configuration in project-local .codex/config.toml files.

model = "default"
model_provider = "mistralrs"
model_context_window = 32768
model_reasoning_summary = "none"
model_supports_reasoning_summaries = false

[model_providers.mistralrs]
name = "mistral.rs"
base_url = "http://localhost:1234/v1"
wire_api = "responses"
request_max_retries = 1
stream_max_retries = 0
stream_idle_timeout_ms = 300000

[profiles.mistralrs]
model = "default"
model_provider = "mistralrs"

Then launch Codex with the mistralrs profile:

codex --profile mistralrs

If a reverse proxy enforces authentication, add env_key = "MISTRALRS_API_KEY" under [model_providers.mistralrs] and export that variable before launching Codex. The local mistral.rs server itself does not validate API keys.

Codex tool calls arrive through /v1/responses as Responses function tools. mistral.rs routes them through the same tool-calling path used by Chat Completions. For direct Responses examples, see the OpenAI Responses API guide.

Claude Code

Claude Code should use the Anthropic-compatible root URL, without /v1. Claude Code appends /v1/messages and /v1/messages/count_tokens itself.

For a persistent local setup, add this to ~/.claude/settings.json or to a project-local .claude/settings.local.json:

{
  "model": "sonnet",
  "env": {
    "ANTHROPIC_BASE_URL": "http://localhost:1234",
    "ANTHROPIC_API_KEY": "not-used",
    "ANTHROPIC_DEFAULT_SONNET_MODEL": "default",
    "ANTHROPIC_DEFAULT_OPUS_MODEL": "default",
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "default",
    "ANTHROPIC_CUSTOM_MODEL_OPTION": "default",
    "ANTHROPIC_CUSTOM_MODEL_OPTION_NAME": "mistral.rs default",
    "ANTHROPIC_CUSTOM_MODEL_OPTION_DESCRIPTION": "Local model served by mistral.rs",
    "CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC": "1"
  }
}

Or set the same values for one shell session:

export ANTHROPIC_BASE_URL=http://localhost:1234
export ANTHROPIC_API_KEY=not-used
export ANTHROPIC_MODEL=sonnet
export ANTHROPIC_DEFAULT_SONNET_MODEL=default
export ANTHROPIC_DEFAULT_OPUS_MODEL=default
export ANTHROPIC_DEFAULT_HAIKU_MODEL=default
export ANTHROPIC_CUSTOM_MODEL_OPTION=default
export CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1
claude

Mapping the Sonnet, Opus, and Haiku defaults to default makes the sonnet setting and Claude Code background or planning calls use the single loaded mistral.rs model. If you serve several models, map each Claude Code default to the local model id you want for that role.

Claude Code client tools arrive as Anthropic tool definitions and later tool_result content blocks. mistral.rs translates these to its internal tool format. For direct Anthropic examples, see the Anthropic Messages API guide.

Server-side agent tools

The coding clients already provide their own editing and shell tools. Server-side mistral.rs tools are separate:

Feature	How it reaches mistral.rs
Client-side tool use	Codex Responses function tools or Claude Code Anthropic tools
Server web search	`web_search_options` or Anthropic `web_search_*` server tools
Server code execution	`enable_code_execution` or Anthropic `code_execution_*` server tools

Server-side web search and code execution require the corresponding mistral.rs agentic runtime flags at server startup. Use them when you want the model server to perform web search or Python execution independently of the coding client’s own terminal tools.

Examples

Copyable config snippets live in examples/server/:

File	What it shows
`codex_config.toml`	User-level Codex provider config for `/v1/responses`.
`claude_code_settings.json`	Claude Code settings for `/v1/messages`.

Troubleshooting

Symptom	Fix
Codex returns 404	Include `/v1` in the Codex provider `base_url`.
Claude Code returns 404	Remove `/v1` from `ANTHROPIC_BASE_URL`.
The client requests an Anthropic model id	Use `default`, or map Claude Code default model env vars to your local ids.
A remote server accepts any key	Put authentication in a reverse proxy. mistral.rs does not validate compatibility API keys.
Claude Code sends beta fields your proxy rejects	Set `CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1` in Claude Code.
Long streams time out	Raise Codex `stream_idle_timeout_ms` or Claude Code `API_TIMEOUT_MS`.