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Gradium is a bundled text-to-speech provider for OpenClaw. The plugin can render normal 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) |
Setup
Create a Gradium API key, then expose it to OpenClaw with either an env var or the config key.
export GRADIUM_API_KEY="gsk_..."
{
messages: {
tts: {
auto: "always",
provider: "gradium",
providers: {
gradium: {
apiKey: "${GRADIUM_API_KEY}",
},
},
},
},
}
apiKey first and falls back to the GRADIUM_API_KEY environment variable.
Config
{
messages: {
tts: {
auto: "always",
provider: "gradium",
providers: {
gradium: {
voiceId: "YTpq7expH9539ERJ",
// apiKey: "${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 | Override the API origin. Trailing slashes are stripped. Defaults to https://api.gradium.ai. |
messages.tts.providers.gradium.voiceId | string | Default voice id used when no directive override is present. |
openclaw.json. See Output below.
Voices
| Name | Voice ID |
|---|
| Emma | YTpq7expH9539ERJ |
| Kent | LFZvm12tW_z0xfGo |
| Tiffany | Eu9iL_CYe8N-Gkx_ |
| Christina | 2H4HY2CBNyJHBCrP |
| Sydney | jtEKaLYNn6iif5PR |
| John | KWJiFWu2O9nMPYcR |
| Arthur | 3jUdJyOi9pgbxBTK |
Per-message voice override
When the active speech policy allows voice overrides, you can switch voices inline using a directive token. All of these resolve to the same voiceId override:
/voice:LFZvm12tW_z0xfGo
/voice_id:LFZvm12tW_z0xfGo
/voiceid:LFZvm12tW_z0xfGo
/gradium_voice:LFZvm12tW_z0xfGo
/gradiumvoice:LFZvm12tW_z0xfGo
Output
The runtime picks the output format from the target surface. The provider does not synthesize other formats today.
| 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.
