For AI agents: a documentation index is available at the root level at /llms.txt and /llms-full.txt. Append /llms.txt to any URL for a page-level index, or .md for the markdown version of any page.
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DocumentationAPI ReferenceIntegrationsAdministrationChangelog
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Changelog

Stay up to date with the latest changes to Synthflow.
May 13, 2026
May 13, 2026
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May 12, 2026

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Synthflow TTS voice model

Synthflow TTS is now available as a voice model option in the agent editor. It delivers low-latency, natural-sounding speech across 32 languages with 12 built-in voices.

The GET /voices endpoint now supports search and provider query parameters for filtering, and voice responses include provider, gender, and languages fields.

Outbound number pooling for agents

You can now assign multiple outbound phone numbers to one agent and choose the caller ID for each outbound call. See the Outbound Number Pooling guide.

EndpointChange
GET /assistants/{model_id}Returns attached_phone_numbers with each attached number’s number, sid, and slug.
PUT /assistants/{model_id}/phone_numbersAttaches multiple outbound numbers using phone_numbers or phone_number_slugs.
DELETE /assistants/…/{phone_number_slug}Detaches one outbound number from the agent.
POST /callsAccepts from_phone_number to select the outbound caller ID for that call.

Knowledge Base API: New Endpoint

You can now update existing knowledge base sources by source ID. The endpoint supports name, url for link and file sources, and content for text sources.

EndpointChange
PUT /sources/{source_id}Updates the source name and type-specific fields.