Five9 vs Retell AI (2026)

Secure tool calling connects AI agents to enterprise systems to perform real-time actions such as authenticating customers, updating records, processing transactions and completing service tasks, which write to a system of record. The Agentic Experience Engine accesses data across systems, and multi-event triggers and business rules fire automation across applications.

A joint solution with Google Cloud connects the Intelligent CX Platform to Gemini Enterprise and Vertex AI, and the platform ships pre-built CRM integrations covering Salesforce, ServiceNow, Microsoft Dynamics 365 and Zendesk with screen pop, click-to-dial and activity logging.

Sourcefive9.com/news/news-releases/five9-launches-breakthrough-new-release-voice-ai-agents-power-next-generationread 2026-09-05

An Apps framework holds credentials for each external system, with agent functions across CRM (Salesforce, HubSpot, Dynamics 365, Zoho, GoHighLevel), helpdesk (Zendesk), scheduling (Calendly, Cal.com) and file storage (Google Drive, OneDrive), plus custom functions calling any HTTP API mid-call, a code tool running JavaScript, and MCP tools and nodes reaching remote MCP servers during a live conversation. Contact data also syncs both ways with the CRM.

Sourcedocs.retellai.com/integrations/overviewread 2026-09-05

Five9's Voice AI Agents run on a harness that enables autonomous workflows through coordinated multi-agent orchestration, with specialized agents working together across complex, multi-step journeys instead of one model handling everything.

The Agentic Experience Engine understands intent in real time, accesses data across systems and orchestrates personalized, goal-driven journeys, and the Agentic Voice Switch is a proprietary architecture that unifies speech, reasoning and voice generation natively in Five9's carrier-grade telephony.

Data, knowledge and orchestration are shared across the whole CX platform, and multi-event triggers and business rules sequence work across applications.

Sourcefive9.com/news/news-releases/five9-launches-breakthrough-new-release-voice-ai-agents-power-next-generationread 2026-09-05

Conversation flow agents are node-and-edge graphs with conversation, subagent, function, code, logic split, extract-variable, SMS, transfer and global nodes, transitions gated by either LLM-evaluated prompt conditions or deterministic equations, reusable subflows shared across flows, and Flex Mode compiling the graph into a runtime prompt for varied caller behavior. Multi-prompt state agents and agent-to-agent transfer cover the same ground for prompt-built agents, with versions and environment tags controlling what is live.

Sourcedocs.retellai.com/build/conversation-flow/overviewread 2026-09-05

Five9 covers voice, digital, chat and social messaging from one platform, and the Agentic Voice Switch is built natively into its own carrier-grade telephony. Work starts when a customer calls or messages, when multi-event triggers and business rules fire automation across applications, and through outbound campaigns and calling lists, with Web2Campaign shown in Five9's developer samples as a route for an external system to push records into a campaign. Voice AI Agents handle the spoken channel end to end and hand off to live agents with context intact.

Sourcefive9.com/products/capabilities/conversational-generative-agentic-airead 2026-09-05

Agents take inbound and outbound calls on Retell-managed numbers or imported ones over elastic SIP trunking, with setup for Twilio, Telnyx, Vonage, Avaya Aura, Genesys Cloud, Five9 and Amazon Connect. They also run browser web calls, a website widget in chat, voice and callback modes, two-way SMS and MMS, and scheduled batch call campaigns, and an inbound call and SMS webhook picks the agent and passes per-call context at ring time.

Sourcedocs.retellai.com/deploy/custom-telephonyread 2026-09-05

Five9's generative AI uses retrieval augmented generation to identify and summarize trusted answers from the customer's knowledge assets, so the agent answers from the enterprise's curated content rather than from model recall. Data, knowledge and orchestration are shared across the whole CX platform, so the same corpus serves self-service, agent assist and summarization. Five9 does not describe the index, refresh behavior, chunking or source level citation.

Sourcefive9.com/products/capabilities/conversational-generative-agentic-airead 2026-09-05

The platform builds and maintains knowledge bases from sources attached as URLs, documents across roughly twenty file formats, or custom text, chunking, embedding and storing them in a vector database at creation time, with retrieval tuned by query-rewrite instructions that condense recent dialogue into a standalone search query. Google Drive and OneDrive sources re-sync on a 24-hour refresh cycle, and knowledge bases are managed independently of any one agent through their own API.

Sourcedocs.retellai.com/build/knowledge-baseread 2026-09-05

Data, knowledge and orchestration are shared across the entire CX platform, the Agentic Experience Engine accesses data across systems to personalize a journey, and handoffs to human agents carry context so a customer does not restart. There is no persistent agent memory store with a set scope, lifetime or deletion control, and no memory product appears in the platform.

Sourcefive9.com/products/capabilities/ai-agentsread 2026-09-05

Contact records keyed by phone number carry custom fields populated by post-call extraction mappings, so the agent recalls preferences, past issues and commitments across every later conversation, with a merged timeline of that contact's calls and chats and a backfill job that re-applies mappings to historical calls. Scope is per contact and the record is separately deletable. It is implemented as contact field mappings, so retention follows the contact record.

Sourcedocs.retellai.com/integrations/build-contact-memoryread 2026-09-05

The dial of trust lets a business set its agents anywhere from fully scripted, for regulated sectors such as banking and healthcare, up to high trust, where the model manages multi-step conversations and calls APIs on its own, so the operator chooses how much latitude the agent has.

Around it sit built-in guardrails, LLM blinding so sensitive data is neither seen nor manipulated by the model, and workflow task verification, all part of an enterprise trust and governance layer that also includes automated post call AI evaluations.

Handoff to a person is a context-rich warm handoff, with AI and human agents working on the same unified platform instead of a cold transfer.

Sourcefive9.com/news/news-releases/five9-launches-breakthrough-new-release-voice-ai-agents-power-next-generationread 2026-09-05

Guardrails detect prohibited topics in both agent responses and user input and replace flagged content with a safe placeholder before it is spoken, and live monitoring lets a person follow the transcript in real time, listen in silently, take over from the agent mid-call or end the call, with an Update Live Call endpoint to inject context or trigger a response on a running session.

Sourcedocs.retellai.com/features/live-monitoringread 2026-09-05

A live trust center lists SOC 2 Type 2, ISO/IEC 27001:2022, ISO/IEC 27017:2015, PCI DSS v4.0.1, HIPAA, HITECH, Cyber Essentials, C5, the CSA STAR registry, TX-RAMP Level 2, CPNI, CCPA, CPRA and GDPR, with a DORA compliance report alongside. The SOC 2 Type 2 report, a HIPAA Type 1 attestation, the ISO 27001 and ISO 27017 certificates and the PCI DSS report are available through an access request, and completed SIG, CAIQ and HECVAT questionnaires are published for due diligence.

Five9 is a Level 1 PCI DSS Service Provider that engages an independent QSA annually across all twelve requirements, and it operates as a HIPAA Business Associate. Multi-Factor Authentication and Audit Logging are named product security features, with Access Log Management, Least Privilege and Password Security under access control. Voice biometrics authenticates the calling consumer and is a product Five9 sells, not a control over the customer's own tenant.

Sourcetrustcenter.five9.comread 2026-09-05

Retell is SOC 2 Type 1 and Type 2 certified and HIPAA and GDPR compliant, with a BAA, a DPA and a GDPR erasure process. Customer controls include role-based access control with Admin, Developer, Analyst and Viewer roles, API keys scoped read or edit per area, a webhook signing key with signature verification and IP allowlisting, expiring signed URLs for recordings and logs, per-agent data storage settings and a per-agent retention policy.

Sourcedocs.retellai.com/general/complianceread 2026-09-05

Audit Logging is listed among the product security features alongside data security and multi-factor authentication, with Access Log Management under access control, so there is a record of who did what on the platform.

AI Agent Studio is the environment to build, test, deploy and monitor Voice AI Agents, automated post-call AI evaluations leave an assessed record of every interaction, and workflow task verification confirms whether the agent completed what it undertook. Five9's reporting layer sits underneath, and its trust and governance layer gives regulated enterprises granular visibility and control. No per decision reasoning trace or tool call log for an individual agent run is published.

Sourcetrustcenter.five9.comread 2026-09-05

A monitor-call WebSocket streams transcript, tool call and node events from a live session, so the path the agent took through the flow is reconstructable turn by turn, backed by session history with transcripts and CSV export, per-call P50, P90 and P99 latency, disconnection reason codes, call_started, call_ended and call_analyzed webhooks, and AI QA scoring calls on hallucination rate, knowledge base accuracy, tool usage, latency and sentiment against customer-defined cohorts.

Sourcedocs.retellai.com/api-references/monitor-call-websocketread 2026-09-05

Delivery is cloud only, serving more than 3,500 enterprises across 140-plus countries, with no self-hosted, on-premise or single-tenant option.

The trust center carries a Data Center Colocations entry under infrastructure alongside business continuity and failover documentation, and the certification set includes region-specific schemes that apply where data is handled locally, C5 for Germany, Cyber Essentials for the United Kingdom, TX-RAMP Level 2 for Texas public bodies, and a DORA compliance report for EU financial entities.

The data center detail sits behind the trust center's access request, and Five9 describes no way for a customer to choose or move its region.

Sourcetrustcenter.five9.comread 2026-09-05

Data storage settings and a retention policy set per agent, plus expiring signed URLs, control what is stored and for how long, but not where data lives. Retell offers no region selection, VPC, single tenant, self hosted or on premises option, and its reliability page describes shared enterprise infrastructure without naming a region.

Sourcedocs.retellai.com/accounts/data-retentionread 2026-09-05

A suite of prepackaged self-service applications and code-free tooling streamlines Intelligent Virtual Agent and AI Agent deployment, so a common use case ships ready to adopt, and AI Agent Studio covers what the packaged set does not. Whether the packaged set can be browsed is not stated.

Sourcefive9.com/products/capabilities/ai-agentsread 2026-09-05

The quick start has the customer pick a template as the first build step, Agent Handbook ships toggleable preset prompt packs for personality, accuracy and safety, and reusable subflows package parts of a conversation flow as shared components adopted across agents. The template catalog sits inside the dashboard, and Retell does not publish how broad it is.

Sourcedocs.retellai.com/get-started/quick-startread 2026-09-05

Models are blended by Five9, not chosen by the customer. Data, knowledge and orchestration are shared across the CX platform, and the Google Cloud partnership integrates the Intelligent CX Platform with Gemini Enterprise and Vertex AI, so more than one model provider is in play, with the Agentic Voice Switch unifying speech, reasoning and voice generation across them and Five9 choosing the model. Customers get no model selector, routing policy or bring your own key path, and the dial of trust governs how much autonomy a model gets, not which model runs.

Sourcefive9.com/news/news-releases/five9-launches-breakthrough-new-release-voice-ai-agents-power-next-generationread 2026-09-05

The customer picks the language model in agent settings and tunes temperature, fast tier, structured output, retries and timeouts, choosing across providers including OpenAI, Anthropic and Google, or runs their own model entirely through the custom LLM WebSocket protocol while Retell handles telephony, transcription and turn-taking. Speech recognition and text-to-speech providers are separately selectable.

Sourcedocs.retellai.com/build/llm-optionsread 2026-09-05

A Developer Program at five9.com/development offers comprehensive Cloud API documentation, a fully-featured sandbox, code samples on GitHub, dedicated developer support and early access to release previews for compatibility testing.

Five9's GitHub organization, Five9DeveloperProgram, publishes working samples against the Agent and Supervisor REST API, the Configuration Web Services API, the CRM SDK, Click-to-Dial and Web2Campaign, and third-party client libraries build against a REST and WebSocket API at api.five9.com covering admin, supervisor and Studio endpoints. AI Agent Studio is the build, test, deploy and monitor environment for Voice AI Agents. The full API documentation and sandbox sit behind Developer Program membership, while the sample repositories are public.

Sourcefive9.com/developmentread 2026-09-05

Retell publishes a REST API at api.retellai.com with an OpenAPI specification and a Postman collection, covering calls, chats, agents, response engines, knowledge bases, contacts, apps, tests and phone numbers. Developers also get official TypeScript and Python SDKs, a browser Web SDK, a command line interface, a hosted MCP server at mcp.retellai.com for Cursor, Claude Desktop and Claude Code, signed webhooks, and an LLM WebSocket protocol for bringing your own model. A published deprecation feed with dated breaking-change notices sits alongside it.

Sourcedocs.retellai.com/api-references/overviewread 2026-09-05

Automated post-call AI evaluations assess every completed interaction instead of a supervisor's sample, and workflow task verification confirms the agent actually completed the task it undertook, giving a readable result on the customer's own agent. AI Agent Studio is a unified environment to build, test, deploy and monitor Voice AI Agents before release, and Developer Program members get a full sandbox plus release previews to test against new versions before general availability. Five9 also reports that containment targets were exceeded across 100,000 calls in an early rollout.

Sourcefive9.com/news/news-releases/five9-launches-breakthrough-new-release-voice-ai-agents-power-next-generationread 2026-09-05

Retell ships five testing surfaces with readable results. An LLM Playground inspects tool calls and transitions and replays any turn, LLM simulation testing has an AI-simulated user run a scenario while success criteria grade each run, and batch tests over many cases report pass rate and per-case results in a testing history. Web and phone call testing and production A/B testing, which splits live traffic between agent versions, complete the set. Test case definitions, batch tests and test runs each have their own API.

Sourcedocs.retellai.com/test/test-overviewread 2026-09-05

Agents act programmatically. Secure tool calling connects them to enterprise systems to authenticate customers, update records and process transactions, pre-built CRM integrations carry screen pop and activity logging into Salesforce, ServiceNow, Dynamics 365 and Zendesk, and the platform exposes REST and WebSocket APIs. Five9 agents work voice and digital CX channels through a carrier-grade telephony platform and do not control a browser, run hosted sessions or automate an interface.

Sourcefive9.com/products/capabilities/ai-agentsread 2026-09-05

Agents cannot control a browser, a desktop session or a remote computer. The Press Digit tool and press digit node let the agent infer and press keypad digits to walk a third party's DTMF input IVR menu on an outbound call, and voicemail handling detects and responds to another system's automated flow.

Sourcedocs.retellai.com/build/single-multi-prompt/press-digitread 2026-09-05