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How LLMs work

Every agent has an LLM model (llm_id) that controls what the agent says and does. The agent and the LLM model are separate resources so you can share one brain across multiple agents — update the system prompt once and every agent using that model picks up the change immediately. 
Agent (voice, first message, call behaviour)
  └── LLM model (system prompt, provider, model, tools, knowledge bases)
When you create an agent, OneInbox automatically creates an LLM model with sensible defaults and returns its id as llm_id.

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Providers

OneInbox supports several LLM providers. Platform providers work out of the box — no credentials needed.
ProviderModelsCredential required
OpenAIgpt-4o, gpt-4o-mini, gpt-5No — platform-provided
Shisashisa-v2-llama3.3-70bNo — platform-provided
Anthropicclaude-sonnet-4-5, claude-haiku-4-5Yes — add an integration
Groqllama-3.3-70b-versatile, gemma2-9b-itYes — add an integration

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Set a system prompt

The system prompt defines the agent’s persona, goals, and rules. Update it at any time without rebuilding the agent: 
curl -X PATCH https://api.oneinbox.ai/v1/models/<llm_id> \
  -H "Authorization: Bearer <api_key>" \
  -H "Content-Type: application/json" \
  -d '{
    "system_prompt": "You are Aria, a friendly sales rep for Acme Corp. Keep replies under two sentences. When the caller says goodbye, call end_call.",
    "temperature": 0.7
  }'
FieldDefaultWhat it does
system_promptGeneral assistantThe agent’s persona, goals, and rules
temperature0.7Creativity. Lower = more consistent, higher = more varied

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Switch provider or model

To use a different provider or model, pass provider and model together: 
curl -X PATCH https://api.oneinbox.ai/v1/models/<llm_id> \
  -H "Authorization: Bearer <api_key>" \
  -H "Content-Type: application/json" \
  -d '{
    "provider": "openai",
    "model": "gpt-4o-mini"
  }'
For Anthropic or Groq, pass credential_id as well: 
curl -X PATCH https://api.oneinbox.ai/v1/models/<llm_id> \
  -H "Authorization: Bearer <api_key>" \
  -H "Content-Type: application/json" \
  -d '{
    "provider": "anthropic",
    "model": "claude-haiku-4-5",
    "credential_id": "<crd_abc123>"
  }'
See Integrations for how to add a credential for Anthropic or Groq.

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Attach tools

Tools give the agent the ability to take actions during a call. They are attached to the LLM model — not to the agent directly: 
curl -X PATCH https://api.oneinbox.ai/v1/models/<llm_id> \
  -H "Authorization: Bearer <api_key>" \
  -H "Content-Type: application/json" \
  -d '{
    "tool_ids": ["<tool_id_1>", "<tool_id_2>"]
  }'
This replaces the full tool_ids list. Include all tool IDs you want active — any not listed are detached. See Tools for how to create tools.

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Attach a knowledge base

Knowledge bases let the agent answer questions from your documents or URLs. They are attached to the agent — not to the LLM model directly: 
curl -X PATCH https://api.oneinbox.ai/v1/agents/<agent_id> \
  -H "Authorization: Bearer <api_key>" \
  -H "Content-Type: application/json" \
  -d '{
    "kb_ids": ["<kb_id_1>", "<kb_id_2>"]
  }'
This replaces the full kb_ids list. Include all knowledge base IDs you want active — any not listed are detached. See Knowledge bases for how to create and manage them.

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Get an LLM model

curl https://api.oneinbox.ai/v1/models/<llm_id> \
  -H "Authorization: Bearer <api_key>"

{
  "id": "llm_xyz789",
  "provider": "openai",
  "model": "gpt-4o-mini",
  "system_prompt": "You are Aria...",
  "temperature": 0.7,
  "tool_ids": ["tool_abc123"]
}

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API reference

List models · Get model · Update model