Gradium

Gradium is a text-to-speech provider for OpenClaw. It renders standard audio replies (WAV), voice-note-compatible Opus output, and 8 kHz u-law audio for telephony surfaces.

Property	Value
Provider id	gradium
Auth	GRADIUM_API_KEY or config apiKey
Base URL	https://api.gradium.ai (default)
Default voice	Emma (YTpq7expH9539ERJ)

Install plugin

Gradium is an official external plugin. Install it, then restart Gateway:

openclaw plugins install @openclaw/gradium-speech
openclaw gateway restart

Setup

Create a Gradium API key, then expose it with an env var or the config key. Config takes precedence over the env var.

Env var

export GRADIUM_API_KEY="gsk_..."

Config key

{
  messages: {
    tts: {
      auto: "always",
      provider: "gradium",
      providers: {
        gradium: {
          apiKey: "${GRADIUM_API_KEY}",
        },
      },
    },
  },
}

Config

{
  messages: {
    tts: {
      auto: "always",
      provider: "gradium",
      providers: {
        gradium: {
          speakerVoiceId: "YTpq7expH9539ERJ",
          // apiKey: "${GRADIUM_API_KEY}",
          // baseUrl: "https://api.gradium.ai",
        },
      },
    },
  },
}

Key	Type	Description
messages.tts.providers.gradium.apiKey	string	Resolved API key. Supports ${ENV} and secret refs.
messages.tts.providers.gradium.baseUrl	string	HTTPS Gradium API URL on api.gradium.ai. Trailing slashes stripped. Default https://api.gradium.ai.
messages.tts.providers.gradium.speakerVoiceId	string	Default voice id used when no directive override is present.

Output format is chosen automatically by target surface (see Output) and is not configurable in openclaw.json.

Voices

Name	Voice ID
Arthur	3jUdJyOi9pgbxBTK
Christina	2H4HY2CBNyJHBCrP
Emma (default)	YTpq7expH9539ERJ
John	KWJiFWu2O9nMPYcR
Kent	LFZvm12tW_z0xfGo
Sydney	jtEKaLYNn6iif5PR
Tiffany	Eu9iL_CYe8N-Gkx_

Per-message voice override

When the active speech policy allows voice overrides, switch voices inline with a directive token (any of these are equivalent, all take a provider-native voice id):

/voice:LFZvm12tW_z0xfGo
/voice_id:LFZvm12tW_z0xfGo
/voiceid:LFZvm12tW_z0xfGo
/gradium_voice:LFZvm12tW_z0xfGo
/gradiumvoice:LFZvm12tW_z0xfGo

If the speech policy disables voice overrides, the directive is consumed but ignored.

Output

Output format is selected by target surface; the provider does not synthesize other formats.

Target	Format	File ext	Sample rate	Voice-compatible flag
Standard audio	wav	.wav	provider	no
Voice note	opus	.opus	provider	yes
Telephony	ulaw_8000	n/a	8 kHz	n/a

Auto-select order

Among configured TTS providers, Gradium’s auto-select order is 30. See Text-to-Speech for how OpenClaw picks the active provider when messages.tts.provider is not pinned.

Related

• Text-to-Speech
• Media Overview