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https://speechify.ai/ SpeechifyAI - Voice AI Research Lab SpeechifyAI is a research lab advancing speech synthesis, voice cloning, and emotional expression — building voice AI indistinguishable from humans. voice ai speechifyai research lab https://speechify.ai/blog/tag/artificial-analysis Posts tagged "artificial-analysis" — SpeechifyAI All blog posts tagged artificial analysis posts tagged speechifyai https://docs.speechify.ai/agents/api-reference/v1/agents/knowledge-bases/-id-/patch Update Knowledge Base | SpeechifyAI API Update a knowledge base. knowledge base update speechifyai api https://speechify.ai/blog/simba-3-2-streaming-model Simba 3.2 is live on the TTS API as the recommended English model — SpeechifyAI Jul 8, 2026 - Simba 3.2 is now available on POST /v1/audio/speech and /v1/audio/stream — a streaming-native Simba 3 model with lower TTFB, richer expressivity, and a curated... https://docs.speechify.ai/agents/api-reference/v1/agents/sip-trunks/get List SIP Trunks | SpeechifyAI API List all SIP trunks in the caller's workspace. Cursor-paginated for uniformity with the other list endpoints: omit cursor for sip trunks list speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/flow/templates/post Create Flow Template | SpeechifyAI API Create a reusable flow template from a graph. create flow template speechifyai api https://docs.speechify.ai/build/api-reference/v1/audio/stream?explorer=true Stream Speech | SpeechifyAI API Synthesize speech and stream the audio back as it is generated, for low-latency playback. Set outputformat in the body for explicit stream speech speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/-id-/evaluation-config/put Update Evaluation Config | SpeechifyAI API Replace the agent's evaluation criteria + data-collection fields. update evaluation config speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/tests/runs/batch Run Tests (Batch) | SpeechifyAI API Queue runs for every (test, agent) pair in the body. Entries without an agentid fan out to every agent the test is run tests batch speechifyai api https://docs.speechify.ai/build/api-reference/get-started/authentication Speechify API Authentication - API Keys and Security | SpeechifyAI API Authenticate Speechify API requests with a Bearer API key. Get and rotate keys in the console, store them securely, and use a server-side proxy for frontends. keys and security api authentication speechify https://docs.speechify.ai/build/guides/text-to-speech/emotion-control Emotion Control in SpeechifyAI Build: SSML Styles | SpeechifyAI API Add emotional expression to Speechify text-to-speech using SSML style tags. 13 supported emotions including cheerful, sad, angry, calm, surprised, and more. emotion control speechifyai build ssml styles api https://docs.speechify.ai/build/changelog/2026/2/19 February 19, 2026 | SpeechifyAI API february speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/tool-definitions/test-mcp-connection Test MCP Connection | SpeechifyAI API Probe a customer-supplied MCP server config without persisting anything. The server opens the configured transport, runs the test mcp connection speechifyai api https://docs.speechify.ai/agents/changelog/2026/6/11 Voice Agents is now publicly available | SpeechifyAI API voice agents is now publicly available speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/conversations/-id-/messages List Messages | SpeechifyAI API Retrieve the transcript for a conversation in startedat order (oldest first). Cursor-paginated: omit cursor to fetch the list messages speechifyai api https://docs.speechify.ai/build/changelog/2026/5/9 API: New simba-3.0 streaming model | SpeechifyAI API api new simba streaming model speechifyai https://docs.speechify.ai/agents/guides/concepts/knowledge-base SpeechifyAI Agents Knowledge Bases - RAG Search | SpeechifyAI API Ground SpeechifyAI Agents in your documents with knowledge bases. Learn how extract, chunk, embed, and index power the built-in search_knowledge tool. speechifyai agents knowledge bases rag search api https://speechify.ai/blog/tag/tts Posts tagged "tts" — SpeechifyAI All blog posts tagged posts tagged tts speechifyai https://docs.speechify.ai/agents/api-reference/v1/agents/tool-definitions/post Create Tool | SpeechifyAI API Create a tool. For webhook tools, the response includes the HMAC webhooksecret exactly once — store it immediately; subsequent create tool speechifyai api https://speechify.ai/blog/changelog SpeechifyAI Changelog — Blog Major changes to the SpeechifyAI platform — cross-product features, infrastructure milestones, and the kind of work that doesn't fit cleanly under either... speechifyai changelog blog https://docs.speechify.ai/build/changelog/2026/7/19 API: published rate & concurrency limits, and a docs_url on 429s | SpeechifyAI API concurrency limits and a https://docs.speechify.ai/build/guides/concepts/models SpeechifyAI Build TTS Models: Simba 3.2, 3.0, Multilingual, and English | SpeechifyAI API Compare Speechify text-to-speech models: Simba 3.2 (recommended, streaming-native English), Simba 3.0 (streaming-native, English + 6 European languages), Simba... speechifyai build https://docs.speechify.ai/build/changelog/2026/7/25 API: canonical Speechify-* header names (legacy X- aliases still work) | SpeechifyAI API legacy x api canonical speechify header https://speechify.ai/trust Trust & Security - SpeechifyAI How SpeechifyAI handles data, security, and reliability for voice AI in production — privacy, encryption, deployment options, access controls, and compliance... trust security speechifyai https://docs.speechify.ai/agents/api-reference/v1/agents/-id-/tools/-toolId-/delete Delete Agent Tool | SpeechifyAI API Remove a tool from the agent. A built-in instance is deleted; an attached external tool is detached (the workspace definition agent tool delete speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/batch-calls/-id-/get Get Batch Call | SpeechifyAI API batch call get speechifyai api https://docs.speechify.ai/build/guides/get-started/official-sdks SpeechifyAI Build SDKs: Python and TypeScript | SpeechifyAI API Install and use the official Speechify API SDKs for Python and TypeScript, or call the REST API directly. Both SDKs read SPEECHIFY_API_KEY automatically. speechifyai build sdks python typescript api https://docs.speechify.ai/agents/api-reference/v1/agents/-id-/tools/get List Agent Tools | SpeechifyAI API List everything this agent can do: built-in capabilities and attached external tool definitions (webhook / client / MCP) in agent tools list speechifyai api https://docs.speechify.ai/?sfy_source=speechify.ai&sfy_page=trust&sfy_placement=footer SpeechifyAI Build: TTS, Voices, Streaming, and SSML | SpeechifyAI API Use SpeechifyAI Build to generate speech, stream long-form audio, clone voices, and control delivery with SSML. speechifyai build tts voices streaming ssml https://x.com/SpeechifyAI Speechify (@SpeechifyAI) / X Available on iOS, Web, Chrome, Mac, and Android. speechify x https://speechify.ai/blog/tag/benchmarks Posts tagged "benchmarks" — SpeechifyAI All blog posts tagged posts tagged benchmarks speechifyai https://docs.speechify.ai/agents/api-reference/v1/agents/tests/folders/post Create Test Folder | SpeechifyAI API Create a test folder. Max depth is 3. create test folder speechifyai api https://speechify.ai/blog/api-key-scopes-and-usage-attribution API keys now carry clearer scopes and usage attribution — SpeechifyAI Jun 30, 2026 - Speechify API keys now have cleaner scope tiers, service-account inheritance, and usage attribution that makes spend easier to trace back to a workload. api keys carry clearer https://docs.speechify.ai/agents/api-reference/v1/agents/phone-numbers/post?explorer=true Import Phone Number | SpeechifyAI API Import a phone number into the workspace. The provider field determines the provisioning path: - livekit - LiveKit purchases the number on your behalf. US phone number import speechifyai api https://docs.speechify.ai/build/changelog/2025/12/24 December 24, 2025 | SpeechifyAI API december speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/flow/templates/-id-/delete Delete Flow Template | SpeechifyAI API Delete a flow template. delete flow template speechifyai api https://docs.speechify.ai/build/api-reference SpeechifyAI Build API - Speech Synthesis, Streaming, and Voice Cloning | SpeechifyAI API SpeechifyAI Build REST API reference. Base URL, Bearer API-key authentication, dated versioning, JSON responses, and endpoints for speech synthesis, streaming,... speechifyai build api synthesis streaming voice https://docs.speechify.ai/build/guides/text-to-speech/streaming SpeechifyAI Build Streaming: Real-Time Speech Audio | SpeechifyAI API Stream SpeechifyAI Build TTS audio in real time with chunked transfer encoding. Begin playback before full generation and handle up to 20,000 characters. speechifyai build real time streaming audio api https://docs.speechify.ai/build/api-reference/get-started/introduction Get started with the SpeechifyAI Build API | SpeechifyAI API Set up on the SpeechifyAI Build API: authenticate with a Bearer key and understand character, rate, and concurrency limits per plan. get started with speechifyai build api https://docs.speechify.ai/agents/guides/account/api-keys SpeechifyAI Agents API Keys - Create and Manage | SpeechifyAI API Create, list, and revoke Speechify API keys to drive Agents from your own code. The plaintext key shows once at creation - copy and store it securely. speechifyai agents api keys create manage https://docs.speechify.ai/agents/api-reference/overview SpeechifyAI Agents API - Real-time voice agents, conversations, and knowledge | SpeechifyAI API SpeechifyAI Agents REST API reference. Endpoints for agents, conversations, knowledge bases, tools, tests, telephony, memory, and audio assets. speechifyai agents real time api voice conversations https://docs.speechify.ai/build/api-reference/v1/audio/speech Create Speech | SpeechifyAI API Synthesize speech audio from text or SSML. Returns the complete audio file plus billing and speech-mark metadata in a single JSON response. create speech speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/-id-/knowledge-bases/get List Agent Knowledge Bases | SpeechifyAI API List knowledge bases attached to an agent. Cursor-paginated: omit cursor for the first page; walk pages while hasmore is true (default page size 50, max 200). knowledge bases list agent speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/outbound-calls?explorer=true Create Outbound Call | SpeechifyAI API Place an outbound call from an agent to a phone number. LiveKit originates the SIP INVITE through the outbound trunk bound to the outbound call create speechifyai api https://docs.speechify.ai/agents/voice-agent-telephony Voice Agent Telephony: Phone Numbers and Calls | SpeechifyAI API Voice agent telephony guide: attach a phone number, take inbound calls, and place outbound and batch calls with the Speechify Agents API. voice agent telephony phone numbers calls speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/-id-/tests/get List Agent Tests | SpeechifyAI API List all tests configured for the agent. Each entry includes the most recent run so a client can render pass/fail badges without list agent tests speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/sip-trunks/post?explorer=true Create SIP Trunk | SpeechifyAI API Create a SIP trunk. For provider=byoc supply sipaddress plus optional digest credentials and IP allowlist. For provider=twilio sip trunk create speechifyai api https://speechify.ai/industries SpeechifyAI by industry Explore SpeechifyAI product use cases by industry. speechifyai industry https://docs.speechify.ai/agents/api-reference/v1/agents/tests/-id-/patch Update Agent Test | SpeechifyAI API Update a test. Only fields present on the request body are changed. agent test update speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/tool-definitions/test-webhook-connection Test Webhook Connection | SpeechifyAI API Probe a customer-supplied webhook tool config without persisting anything. The server fires the exact request shape used on a real test webhook connection speechifyai api https://speechify.ai/blog/audio-404s-diagnosable-by-cause TTS 404s now name the fix instead of a generic not-found — SpeechifyAI Jul 27, 2026 - POST /v1/audio/speech, /stream, and /stream/with-timestamps now return voice_not_found or a model-not-found message on a missing voice or model, instead of an... https://docs.speechify.ai/build/api-reference/v1/voices/-id-/delete Delete Voice | SpeechifyAI API Delete a personal (cloned) voice delete voice speechifyai api https://speechify.ai/blog/hello-speechify-developers Hello Speechify Developers — SpeechifyAI Jun 19, 2026 - Welcome to the new Speechify developer blog. Expect updates from the AI and labs teams, product news, collaborations, and technical guides for the Speechify... hello speechify developers https://speechify.ai/build SpeechifyAI Build, One API for Text-to-Speech and Cloning One developer API for voice AI: text-to-speech and voice cloning on the Simba models, from $6 per 1M characters. One key, one bill, 50K free. text to speech speechifyai build one api cloning https://docs.speechify.ai/build/api-reference/get-started/spend-limits Per-Key Monthly Spend Limits | SpeechifyAI API Set a monthly USD spend limit on any Speechify API key. Requests are refused with 402 spend_cap_exceeded once the key reaches its limit; the limit resets each... spend limits per key monthly speechifyai https://docs.speechify.ai/agents/guides/phone-numbers/add-a-phone-number Add or Import a Phone Number for SpeechifyAI Agents | SpeechifyAI API Import a phone number from LiveKit, Twilio, or your own SIP trunk into Speechify, add a label, and bind it to an agent that answers inbound calls. phone number speechifyai agents add import api https://docs.speechify.ai/build/streaming-tts-guide Streaming TTS Guide: Low-Latency Speech Audio | SpeechifyAI API Streaming text-to-speech guide: call POST /v1/audio/stream to receive audio chunks in real time, begin playback early, and handle up to 20,000 characters. streaming tts guide low latency speech audio api https://docs.speechify.ai/build/api-reference/get-started/api-limits Speechify API Limits: Characters, Rate, and Concurrency | SpeechifyAI API Reference for Speechify API limits: 2,000-character speech and 20,000-character stream requests, per-plan rate and concurrency limits, and handling 429 errors. api limits speechify characters rate concurrency https://docs.speechify.ai/agents/api-reference/v1/agents/conversations/get List Conversations | SpeechifyAI API List conversations owned by the caller, ordered by most recent. Cursor-paginated: omit cursor to fetch the first page; pass the list conversations speechifyai api https://docs.speechify.ai/?sfy_source=speechify.ai&sfy_page=pricing&sfy_placement=footer SpeechifyAI Build: TTS, Voices, Streaming, and SSML | SpeechifyAI API Use SpeechifyAI Build to generate speech, stream long-form audio, clone voices, and control delivery with SSML. speechifyai build tts voices streaming ssml https://docs.speechify.ai/build/guides/voice-cloning/overview Voice Cloning with SpeechifyAI Build | SpeechifyAI API Clone a custom voice from a 10-30 second sample with the Speechify API: create the voice, use it in any speech request, and delete it when done. voice cloning speechifyai build api https://docs.speechify.ai/agents/api-reference/get-started/api-limits Speechify API Limits: Characters, Rate, and Concurrency | SpeechifyAI API Reference for Speechify API limits: 2,000-character speech and 20,000-character stream requests, per-plan rate and concurrency limits, and handling 429 errors. api limits speechify characters rate concurrency https://docs.speechify.ai/agents/api-reference/v1/agents/flow/templates/get List Flow Templates | SpeechifyAI API List the reusable flow templates available to the workspace. Cursor-paginated: omit cursor for the first page; walk pages flow templates list speechifyai api https://speechify.ai/industries/agents/real-estate Real Estate voice agents — SpeechifyAI From lead qualification and showing scheduling to tenant support and maintenance requests, SpeechifyAI voice agents automate every phone-driven workflow across... real estate voice agents speechifyai https://speechify.ai/blog/tag/voice-cloning Posts tagged "voice-cloning" — SpeechifyAI All blog posts tagged voice cloning posts tagged speechifyai https://docs.speechify.ai/build/guides/concepts/spend-limits Per-Key Monthly Spend Limits | SpeechifyAI API Set a monthly USD spend limit on any Speechify API key. Requests are refused with 402 spend_cap_exceeded once the key reaches its limit; the limit resets each... spend limits per key monthly speechifyai https://docs.speechify.ai/build/changelog/2026/7/27 API: Free tier gets a burst allowance on /v1/audio/* | SpeechifyAI API free tier api gets https://speechify.ai/compare/agents/bland SpeechifyAI vs Bland — SpeechifyAI Bland is known for high-volume outbound with a clean all-in number ($0.11–0.14/min) — but the lower rate sits behind a $299–499/mo platform fee. SpeechifyAI is... vs bland speechifyai https://docs.speechify.ai/build/api-reference/overview SpeechifyAI Build API - Speech Synthesis, Streaming, and Voice Cloning | SpeechifyAI API SpeechifyAI Build REST API reference. Base URL, Bearer API-key authentication, dated versioning, JSON responses, and endpoints for speech synthesis, streaming,... speechifyai build api synthesis streaming voice https://docs.speechify.ai/agents/api-reference/v1/agents/conversations/-id-/memories List Conversation Memories | SpeechifyAI API List memories extracted from a specific conversation. list conversation memories speechifyai api https://speechify.ai/blog/api-key-monthly-spend-limits API keys can now enforce monthly USD spend limits — SpeechifyAI Jul 2, 2026 - Speechify API keys can now carry a monthly USD spend limit, returning 402 spend_cap_exceeded once a key reaches its budget for the calendar month. api keys spend limits enforce https://docs.speechify.ai/agents/api-reference/get-started/introduction Get started with the SpeechifyAI Agents API | SpeechifyAI API Set up on the SpeechifyAI Agents API: authenticate with a Bearer key and understand rate and concurrency limits per plan. get started with speechifyai agents api https://docs.speechify.ai/agents/api-reference/v1/agents/phone-numbers/available Search Available Phone Numbers | SpeechifyAI API Search carrier inventory for phone numbers available to purchase. Currently restricted to the US (country=US); pass areacode phone numbers search available speechifyai api https://speechify.ai/blog/tts-free-tier-burst-allowance Free tier TTS requests get a burst allowance — SpeechifyAI Jul 27, 2026 - Free-tier /v1/audio/* requests get a 10-request burst bucket instead of capping at the 1 req/s sustained rate, so a first quickstart script no longer 429s on... free tier get a tts requests burst https://speechify.ai/blog/building-an-automated-audiobook-pipeline-with-the-speechify-tts-api Building an automated audiobook pipeline with the Speechify TTS API — SpeechifyAI Jul 3, 2026 - Turn long-form ePub or Markdown into a single narrated chapter MP3 with a runnable Python demo: chunk on sentence boundaries, synthesize each chunk, stitch... https://speechify.ai/blog/best-tts-providers-2026-comparison Best TTS Providers 2026: Comparison of the Top 10 APIs — SpeechifyAI Jul 23, 2026 - The top 10 text-to-speech APIs of 2026, benchmarked on the independent Artificial Analysis Speech Arena. Simba 3.2 is tied for the best-rated voice at $6 to... of the https://speechify.ai/blog/multilingual-voice-agents Voice agents can now switch language mid-call — SpeechifyAI Jul 24, 2026 - One agent serves multiple languages in a single session, with no transfer and no dropped context - configure it with additional_languages. voice agents switch language mid call speechifyai https://docs.speechify.ai/agents/api-reference/v1/agents/ivr-menus/-id-/get Get IVR Menu | SpeechifyAI API Fetch one menu's full shape. Returns 404 for missing, soft-deleted, or foreign-tenant menus — existence information is never leaked across tenants. get ivr menu speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/-id-/evaluation-config/get Get Evaluation Config | SpeechifyAI API Retrieve the agent's post-call evaluation criteria + data-collection config. get evaluation config speechifyai api https://docs.speechify.ai/?sfy_source=speechify.ai&sfy_page=models&sfy_placement=models-docs SpeechifyAI Build: TTS, Voices, Streaming, and SSML | SpeechifyAI API Use SpeechifyAI Build to generate speech, stream long-form audio, clone voices, and control delivery with SSML. speechifyai build tts voices streaming ssml https://docs.speechify.ai/agents/guides/configure-an-agent Configure a Speechify Voice Agent: Prompt, Voice, Language | SpeechifyAI API Configure every field on a Speechify agent's Agent tab: name, first message, system prompt, voice, and language, then save changes for the next call. voice agent configure speechify prompt language https://docs.speechify.ai/agents/changelog/2026/7/20 API: per-agent max_call_duration_seconds | SpeechifyAI API agent max api per call duration https://docs.speechify.ai/agents/api-reference/v1/agents/-id-/flow/versions/-versionId- Get Agent Flow Version | SpeechifyAI API Return the full flow graph for a specific published version. get agent flow version speechifyai api https://docs.speechify.ai/agents/guides/get-started/enterprise-sso Speechify Enterprise SSO - SAML/OIDC single sign-on | SpeechifyAI API Set up enterprise SAML or OIDC single sign-on for a Speechify workspace through the WorkOS Admin Portal. Owners and admins connect an identity provider once;... single sign on enterprise sso speechify saml oidc https://docs.speechify.ai/build/changelog/2026/7/10 API: cloned voices on simba-3.2 (manual approval) | SpeechifyAI API manual approval api cloned voices simba https://speechify.ai/blog/author/luke Luke Oliff — SpeechifyAI Luke Oliff is a Developer Relations leader based in the UK. For the better part of a decade he has been working with voice technology, developer tooling, and... luke oliff speechifyai https://docs.speechify.ai/agents/guides/phone-numbers/batch-calls Batch Outbound Phone Calls with SpeechifyAI Agents | SpeechifyAI API Place outbound calls to many recipients in one request with a Speechify agent: send per-call variables, schedule batches up to 30 days ahead, and track status. phone calls speechifyai agents batch outbound api https://docs.speechify.ai/?sfy_source=speechify.ai&sfy_page=blog-simba-3-tops-artificial-analysis-tts-leaderboard&sfy_placement=migration-sdks&sfy_product=build SpeechifyAI Build: TTS, Voices, Streaming, and SSML | SpeechifyAI API Use SpeechifyAI Build to generate speech, stream long-form audio, clone voices, and control delivery with SSML. speechifyai build tts voices streaming ssml https://docs.speechify.ai/agents/api-reference/v1/agents/memories/-memoryId- Delete Memory | SpeechifyAI API Soft-delete one memory row. delete memory speechifyai api https://speechify.ai/blog/speechify-version-api-date-pinning Speechify-Version gives API clients a stable date pin — SpeechifyAI Jun 25, 2026 - Speechify APIs now support the Speechify-Version header, so HTTP clients can pin a dated contract while SDKs send their build-date version automatically. api clients speechify version gives https://speechify.ai/blog/tts-output-format-sample-rate-bitrate TTS now accepts sample-rate and bitrate-specific output formats — SpeechifyAI Jul 2, 2026 - Speechify TTS speech and streaming endpoints now accept output_format values like pcm_16000, ulaw_8000, and bitrate-tuned mp3 variants without changing... sample rate https://speechify.ai/blog Blog — SpeechifyAI Technical writing across Speechify Labs (voice AI research), SpeechifyAI (the product), SpeechifyAI API (developer-facing engineering), and the SpeechifyAI... blog speechifyai https://speechify.ai/industries/agents/financial-services Financial Services voice agents — SpeechifyAI From account inquiries and loan origination to claims processing, collections, and compliance verification, SpeechifyAI voice agents automate customer and... financial services voice agents speechifyai https://docs.speechify.ai/build/changelog/2026/6/27 API: GET /v1/voices returns an object envelope | SpeechifyAI API api get voices returns object https://docs.speechify.ai/build/changelog/2026/6/28 API: voice-gender value notSpecified is now not_specified | SpeechifyAI API api voice is now not specified gender value https://docs.speechify.ai/agents/voice-agent-api Voice Agent API: Build a Realtime Voice Agent | SpeechifyAI API Voice agent API guide: create an agent with POST /v1/agents, start a realtime conversation, and embed it. Speech, LLM, and telephony in one API. voice agent api build realtime speechifyai https://docs.speechify.ai/build/guides/concepts/api-versioning API Versioning | SpeechifyAI API How Speechify API date-based versioning works, including the Speechify-Version header, workspace defaults, and deprecation windows. api versioning speechifyai https://docs.speechify.ai/agents/api-reference/v1/agents/knowledge-bases/get List Knowledge Bases | SpeechifyAI API List knowledge bases owned by the caller. Cursor-paginated: omit cursor to fetch the first page. The default page size is knowledge bases list speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/-id-/get Get Agent | SpeechifyAI API Retrieve a voice agent by ID. get agent speechifyai api https://docs.speechify.ai/agents/api-reference/v1/agents/conversations/-id-/shadow-token Mint shadow-call token | SpeechifyAI API Mint a listen-only realtime access token so an authorized observer can join an ongoing voice-agent conversation as a hidden mint shadow call token speechifyai