ElevenLabs Agents API + MCP vs Hume EVI (Empathic Voice Interface)

ElevenLabs Agents API + MCP

API keys scoped to endpoint groups, with per-key credit limits and service accounts. $0.08 a minute excludes LLM tokens and carrier minutes.

Hume EVI (Empathic Voice Interface)

Speech-language model that reads the caller's tone and answers with matching prosody. One account-wide key, sent in the WebSocket and Twilio webhook URLs.

ElevenLabs Agents API + MCP

1. Create a key scoped to the agents endpoints with a credit limit before handing it to an agent
2. Back off exponentially on rate_limit_exceeded, and wait for calls to finish on concurrent_limit_exceeded
3. Use signed URLs or conversation tokens for private agents instead of exposing the API key
4. Set platform_settings.privacy.retention_days where you don't need 2 years of history
5. Pick a low-latency LLM, the pipeline waits on it every turn

Hume EVI (Empathic Voice Interface)

1. Create a config with a voice first, EVI 3 has no default
2. Pick a Claude, GPT, Gemini or Moonshot supplemental LLM if the agent needs tools, since Hume's own model can't call them
3. Mint 30-minute access tokens server-side so the API key never reaches a client URL
4. Turn on 'Do not retain data' and 'Do not use for training' at app.hume.ai before sensitive calls
5. Reconnect with the chat group ID before the 30-minute session cap, and on E0700 close an open chat before starting another