ElevenLabs Text to Speech API + MCP vs HeyGen Voice

ElevenLabs Text to Speech API + MCP

Keys can be limited to chosen endpoints and given a credit quota, and service accounts hold keys that don't belong to a person. The Terms let ElevenLabs train on content unless you opt out, which the Eleven v4 launch page contradicts, and v4 runs through Text to Dialogue rather than the classic text-to-speech endpoint.

HeyGen Voice

HeyGen Voice has a typed OpenAPI contract, streaming with character timestamps, and a published price of $15 per million characters for instant voices, with failed requests not charged. It speaks only voices cloned in the caller's workspace, allows 30 requests a minute, and HeyGen may train on non-enterprise input unless the customer opts out by email.

ElevenLabs Text to Speech API + MCP

1. Call Eleven v4 through POST /v1/text-to-dialogue and set model_id to eleven_v4, because that endpoint defaults to eleven_v3.
2. Retrain an older Instant or Professional Voice Clone on v4 before using it there, since earlier clones aren't tuned for the new model.
3. Spell out numbers yourself on eleven_flash_v2_5, which doesn't normalise them by default, and turning that on is Enterprise only.
4. On 429 read code, back off on rate_limit_exceeded and wait for running requests on concurrent_limit_exceeded.
5. Give the agent a key scoped to Text to Speech with a credit quota.

HeyGen Voice

1. Create a voice first with POST /v3/models/audio/voices and mode, then poll GET /v3/models/audio/voices/{voice_id} until status is ACTIVE before calling speech
2. Send expressiveness_boost only for instant voices and seed, speed, pitch_shift, pitch_variance or <break> tags only for professional voices. Mixing them returns 400 invalid_parameter
3. On the stream, decode and play each base64 WAV part in part_index order. Do not concatenate the bytes
4. Send an Idempotency-Key when creating a voice, and retry 502, 503 and 504 on speech, which the OpenAPI file marks as safe
5. Use POST /v3/voices/speech for stock or designed voices. It is a different engine and price