Nexus Auto

Nexus Auto picks a Fireworks open model or an Anthropic or OpenAI model for each turn. Set it up in a coding harness, an LLM gateway, or an SDK.

Use the model ID auto.

• Easy turns go to a Fireworks open model.
• Harder turns go to an Anthropic or OpenAI model on your own account.
• You pay the chosen model’s rate for each turn, not a closed model’s rate on every turn.

Nexus Auto was formerly FireRouter. The firerouter model ID no longer works; use auto instead.

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Which models auto can use

With only your Fireworks key, auto uses Fireworks open models. If you connect an Anthropic or OpenAI Provider Key, it can also use those models.

To keep auto on open models only, run nexus auto --providers fireworks.

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Set up

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Nexus CLI

Connect your tool with Nexus Desktop or the Nexus CLI. Both set the model to auto:

nexus claude   # or codex, chatgpt, cursor, vscode, and more

Setup steps for each tool are in Coding Harnesses.

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LLM gateway

Point your LLM gateway, such as LiteLLM or Portkey, at Fireworks with your Fireworks API key and the model auto. Clients behind the gateway use only their gateway key.

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API and SDK

Point the OpenAI SDK at Fireworks and set the model to auto:

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_FIREWORKS_API_KEY",
    base_url="https://api.fireworks.ai/inference/v1",
)

response = client.chat.completions.create(
    model="auto",
    messages=[{"role": "user", "content": "Say pong in one word."}],
)
print(response.model, response.choices[0].message.content)

auto also works with the Anthropic SDK and the Responses API. Examples for both are in APIs and SDKs.

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Provide Anthropic and OpenAI credentials

Nexus Auto calls closed models through your own Anthropic, OpenAI, or Amazon Bedrock account.

• Provider Keys (recommended): an admin connects the key once in Nexus settings, and it applies to everyone on the account.
• Request headers: send x-anthropic-api-key or x-openai-api-key with each request.

Without a credential for a provider, Nexus Auto uses the other models.

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Check which model served a turn

The response model field names the model that served the turn, such as glm-5p3 or claude-opus-5-5. In Claude Code, the status line also shows it.

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Cost and effort

• Open models bill to your Fireworks account at serverless rates.
• Closed models bill to the Anthropic or OpenAI account whose credential served the turn.
• Set effort in your tool. Higher effort asks for a more thorough attempt.

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Supported models

Family	Model IDs	Credential
Claude Opus, Sonnet, Fable	claude-opus-5-5, claude-sonnet-5-5, claude-fable-5-1	Anthropic
GPT Sol, Astra, Luna	gpt-6.1-sol, gpt-6-astra, gpt-6-luna	OpenAI
Kimi, GLM, DeepSeek	kimi-k3, kimi-k3-fast, glm-5p3, glm-5p3-fast, glm-5p3-flash, deepseek-v4p1-flash	Fireworks

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Pin a specific model

On Enterprise, to use one model for every turn, use its ID instead of auto, such as nexus claude --model glm-5p3 or "model": "glm-5p3" in a request.

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Web search

Web search is built into Nexus. In Claude Code, Claude Desktop, Codex, and ChatGPT, the app’s native web search remains available. Fireworks runs the search server-side, so no search MCP server is required.

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Troubleshooting

Nexus Auto never uses an Anthropic or OpenAI model. No closed-model credential is reaching it. Run nexus auto to see what’s connected, and connect a Provider Key if none is.