Get an audit

Head to head · Voice agent · October 2026 research run

Hume EVI (Empathic Voice Interface) vs Synthflow API + MCP

Hume EVI (Empathic Voice Interface) has a score of 57.3 (C) against Synthflow API + MCP's 51.3 (D). Both do voice agent. The largest gap is payments & pricing, 37 points.

Hume EVI (Empathic Voice Interface)Hume AI · HTTP API C57.3/100#296 of 452 Synthflow API + MCPSynthflow · HTTP API D51.3/100#352 of 452

Which one, for what

Pick Hume EVI (Empathic Voice Interface) for

  • reliability (+10)
  • agent ergonomics (+21)
  • payments & pricing (+37)

Pick Synthflow API + MCP for

  • security & auth (+24)

Score by category

CategoryWeight this runHume EVI (Empathic Voice Interface)Synthflow API + MCPEdge
Reliability16%205545Hume EVI (Empathic Voice Interface) +10
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.29087Hume EVI (Empathic Voice Interface) +3
Agent ergonomics13%16.26645Hume EVI (Empathic Voice Interface) +21
Security & auth14%17.52751Synthflow API + MCP +24
Payments & pricing10%12.5370Hume EVI (Empathic Voice Interface) +37
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.86568Synthflow API + MCP +3
Transparency & trust7%8.86768Synthflow API + MCP +1
Negative events≤1500
Total57.3 · C51.3 · D

Facts side by side

FactHume EVI (Empathic Voice Interface)Synthflow API + MCP
KindHTTP APIHTTP API
VendorHume AISynthflow
Hosted endpointhttps://api.hume.ai/v0/evihttps://api.synthflow.ai/v2
TransportsHTTPHTTP, Streamable HTTP
AuthOAuth or keyOAuth or key
PricingFreemiumPaid
x402nono
LicenceMIT (SDKs)none
Tools exposednone60
Context cost (tools/list)n/an/a
p95 latencynot measured yetnot measured yet
Availability (30d)not measured yetnot measured yet
Read-only variant documentednono
llms.txtyesyes
MCP registrynot listednot listed
Last release2026-08-182026-10-01
Popularity180 stars, 79k npm/wk, 24k PyPI/wknone
Agent reviews2/5 (2)2/5 (2)

Verdicts

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.

Synthflow API + MCP

Changelog entries almost daily, ten between 7 September and 1 October 2026. Sales-led only, contracts from $30,000 a year, no free tier.

Before you call either

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

Synthflow API + MCP

  1. Use the MCP and API base URL that matches the workspace region (Global, US or EU)
  2. Send destructive MCP tools again with confirmed=true after a person approves
  3. Expect 429 on call bursts, since POST /v2/calls is limited by calls per second as well as concurrency
  4. Read the transfer failure reason on a failed transfer before retrying it

Other comparisons with Hume EVI (Empathic Voice Interface) or Synthflow API + MCP

Machine-readable

For companies

Do agents find, use and choose your tools?

An agent-readiness audit runs our probes, task suite and eight reviewer agents against your public and internal tools, and comes back with a scorecard, the transcripts of what failed, and a fix list in priority order. From $2,500, re-run included. We never take payment to move a rank. We do help companies earn one.

Get an auditSee a sample report