Documentation Index
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Telnyx AI Assistants support multiple speech-to-text (STT) models for transcribing caller audio. The model you choose affects transcription accuracy, supported languages, and response latency. You can also tune provider-specific transcription behavior, such as end-of-turn detection, formatting, keyterm boosting, and Azure region selection.
Available models
| Model | Engine | Best for |
|---|
deepgram/flux | Deepgram | Conversational AI, optimized for turn-taking, English only |
deepgram/nova-3 | Deepgram | Fast multilingual transcription, recommended for multilingual assistants |
deepgram/nova-2 | Deepgram | Fast multilingual transcription on Deepgram’s previous-generation model |
azure/fast | Azure | Fast multilingual transcription with optional Azure region and API key configuration |
assemblyai/universal-streaming | AssemblyAI | Conversational, multilingual streaming transcription with configurable turn detection |
xai/grok-stt | xAI | Multilingual transcription using Grok STT |
deepgram/flux is English-only. For multilingual assistants, use deepgram/nova-3, deepgram/nova-2, azure/fast, assemblyai/universal-streaming, or xai/grok-stt.
Selecting a model
Portal
In the AI Assistants tab, edit your assistant and navigate to the Voice tab. Select your preferred STT model from the Transcription Model dropdown.
When you change models in the Portal, related settings are reset to the defaults for that provider. For example:
deepgram/flux sets language to English and applies Flux end-of-turn defaults.- Other Deepgram models enable
smart_format and numerals by default.
assemblyai/universal-streaming applies AssemblyAI turn detection defaults.azure/fast defaults the Azure region to latency, which auto-selects the closest supported Telnyx-managed region.
API
Set the transcription.model field when creating or updating an assistant:
curl -X POST https://api.telnyx.com/v2/ai/assistants \
-H "Authorization: Bearer $TELNYX_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"name": "My Assistant",
"model": "anthropic/claude-haiku-4-5",
"instructions": "You are a helpful voice assistant.",
"transcription": {
"model": "deepgram/flux"
}
}'
auto, supported models auto-detect the language:
"transcription": {
"model": "deepgram/nova-3",
"language": "es"
}
Languages
Supported language options depend on the selected model.
| Model | Language behavior |
|---|
deepgram/flux | English only |
deepgram/nova-3 | Auto-detect plus supported Deepgram Nova 3 language codes |
deepgram/nova-2 | Auto-detect plus supported Deepgram Nova 2 language codes |
azure/fast | Explicit Azure locale codes, such as en-US, es-MX, or fr-FR |
assemblyai/universal-streaming | auto for multilingual detection or en for English |
xai/grok-stt | auto plus supported Grok STT language codes |
Deepgram settings
Deepgram Flux end-of-turn detection
deepgram/flux is optimized for live voice agents. It provides end-of-turn detection so the assistant can start responding as soon as the caller finishes speaking. It also supports eager end-of-turn, which starts large language model (LLM) processing before the caller fully stops speaking to reduce perceived response latency.
When you select deepgram/flux in the Portal, these settings are applied by default:
| Field | Type | Range | Portal default | Description |
|---|
eot_threshold | number | 0.5-0.9 | 0.8 | Confidence required to trigger a final end of turn. Higher values require more confidence and may add latency. |
eot_timeout_ms | integer | 500-10000 | 5000 | Maximum silence duration, in milliseconds, before forcing an end of turn. |
eager_eot_threshold | number | 0.3-0.9 | 0.4 | Confidence required to start speculative LLM processing before final end-of-turn confirmation. Lower values trigger earlier. |
eager_eot_threshold must be less than or equal to eot_threshold. Setting both thresholds to the same value effectively disables eager end-of-turn behavior because the system waits for final end-of-turn confirmation before starting LLM processing.
The eager_eot_threshold field is controlled by the FE-eager-eot-threshold Portal feature flag. When that flag is disabled, the Portal hides the field, but API payloads can still include it if your account supports the setting.
0.1 seconds for wait time and endpointing plan thresholds.
Keyterm Boost
deepgram/flux and deepgram/nova-3 support keyterm, a comma-separated list of terms to boost during recognition. Use it for product names, customer names, acronyms, or domain-specific vocabulary.
Keyterm Boost also supports dynamic variables. Use variables when boosted terms are caller-specific, such as a customer name, participant names, account name, or product names passed into the assistant at conversation start.
"transcription": {
"model": "deepgram/nova-3",
"settings": {
"keyterm": "Telnyx,VoIP,SIP,{{customer_name}},{{product_name}}"
}
}
| Field | Type | Default | Description |
|---|
smart_format | boolean | true | Automatically formats transcripts for readability, including punctuation and casing. |
numerals | boolean | true | Converts spoken numbers to digits, for example “five hundred” to “500”. |
AssemblyAI settings
assemblyai/universal-streaming supports configurable turn detection. When you select it in the Portal, these defaults are applied:
| Field | Type | Range | Portal default | Description |
|---|
end_of_turn_confidence_threshold | number | 0-1 | 0.4 | Confidence required to trigger an end of turn. Higher values require more certainty before ending a turn. |
min_turn_silence | integer | 100-5000 | 400 | Minimum silence duration, in milliseconds, before a turn can end. |
max_turn_silence | integer | 100-5000 | 1280 | Maximum silence duration, in milliseconds, before forcing an end of turn. |
min_turn_silence must be less than or equal to max_turn_silence.
"transcription": {
"model": "assemblyai/universal-streaming",
"language": "auto",
"settings": {
"end_of_turn_confidence_threshold": 0.4,
"min_turn_silence": 400,
"max_turn_silence": 1280
}
}
Azure settings
azure/fast supports region selection and an optional Azure API key reference.
| Field | Type | Description |
|---|
region | string | Azure transcription region. The Portal defaults to latency, which auto-selects the closest supported Telnyx-managed region. |
api_key_ref | string | Optional integration secret reference for your Azure API key. When provided, the Portal only shows regions that support custom API keys. |
latency, australiaeast, centralindia, eastus, northcentralus, westeurope, and westus2. Additional Azure regions are available when using your own Azure API key.
"transcription": {
"model": "azure/fast",
"language": "en-US",
"region": "latency"
}
Create an assistant with tuned transcription settings:
curl -X POST https://api.telnyx.com/v2/ai/assistants \
-H "Authorization: Bearer $TELNYX_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"name": "Low Latency Assistant",
"model": "anthropic/claude-haiku-4-5",
"instructions": "You are a helpful voice assistant.",
"transcription": {
"model": "deepgram/flux",
"language": "en",
"settings": {
"eot_threshold": 0.8,
"eot_timeout_ms": 5000,
"eager_eot_threshold": 0.4,
"keyterm": "Telnyx,VoIP,SIP,{{customer_name}},{{product_name}}"
}
}
}'
