API Changelog

GPT-5.1 is now supported

Added GPT-5.1 support for agents.

• POST /assistants/ (Create an agent)
• PUT /assistants/:model_id/ (Update an agent)

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 "agent": {
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    "llm": "gpt-5.1"
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  }

Knowledge Base Sources: Content field added

Added a new content field to the knowledge base sources endpoint to provide text content directly when adding text sources.

• PDF/Web sources: Use url field with a link to the hosted file or webpage
• Text sources: Use content field to provide text directly

Endpoint:

• POST /knowledge_base/:knowledge_base_id/sources

List Calls Response Update

The GET /v2/calls endpoint now returns additional call metadata and pagination information to provide more comprehensive call details.

New Fields:

• pagination object with total_records, limit, and offset for paginated responses
• judge_results — Call quality judging results
• agents_used — Array of agents used during the call
• executed_actions — Actions executed during the call
• type_of_call — Call direction (inbound/outbound)
• error_message — Error details if call failed
• call_status — Current status of the call
• labels — Array of labels associated with the call
• agent_phone_number — Phone number used by the agent
• deployment_type — Type of deployment
• name — Name of the call recipient

Removed Fields:

• timeline, recording_sid, and voice_engine_type are no longer returned

New Webhook Logs Endpoints

We’ve added two endpoints to manage Webhook Logs programmatically.

Endpoints Added:

• GET /logs — List webhook logs
• GET /logs/:webhook_log_id — Retrieve a webhook log by ID

New Simulations Endpoints

We’ve added a comprehensive set of new endpoints to manage Simulation Cases and Simulation Sessions programmatically.

• Case Management: Create, list, retrieve, update, delete, and generate simulation cases.
• Session Management: Start a simulation and list/retrieve simulation sessions.
• Listings: List simulation cases by agent and list all simulations.

Endpoints Added:

• POST /simulations — Create a simulation case
• GET /simulations — List simulation cases
• GET /simulations/:case_id — Get a simulation case
• PUT /simulations/:case_id — Update a simulation case
• DELETE /simulations/:case_id — Delete a simulation case
• POST /simulations/generate — Generate simulation cases
• GET /simulations/agent/:agent_id — List simulation cases by agent
• POST /simulations/start — Start a simulation
• GET /sessions — List simulation sessions
• GET /sessions/:session_id — Get a simulation session
• GET /simulations/all — List simulation cases
• GET /simulations/:case_id — Get a simulation case

Read more about the feature here: https://docs.synthflow.ai/simulations

Subaccount Update: Import/Return Products

Added support to the update subaccount endpoint to manage importing objects like phone numbers from the parent workspace to subaccounts.

• New optional field operation_type (string): allowed values import, return.
• New optional field products.phone_numbers[].number to specify E.164 numbers to import to or return from the subaccount_id.

• PUT /subaccounts/:subaccount_id — Update a subaccount

New timeout value for custom actions

You can now specify a failure_timeout field when creating or updating a custom action. This allows you to control how long a custom action is allowed to run before it is automatically terminated if the timeout is reached.

Deprecated Language Value

The es language code is no longer supported. Please use es-ES for Spanish when creating or updating agents.

• POST /assistants/ — Create an agent
• PUT /assistants/:model_id/ — Update an agent

Phone books: new API endpoints

New endpoints added:

• POST /phonebooks/ (Create a phone book)
• GET /phonebooks/ (List phone books)
• DELETE /phonebooks/:phone_book_id/ (Delete a phone book)
• POST /phonebooks/:phone_book_id/entries/ (Create a phone book entry)
• DELETE /phonebooks/:phone_book_id/entries/:entry_id (Delete a phone book entry)

GPT-5 is now supported

Added GPT-5 support for agents.

• POST /assistants/ (Create an agent)
• PUT /assistants/:model_id/ (Update an agent)

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 "agent": {
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    "llm": "gpt-5-chat"
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  }