Vapi vs. Retell AI for engineering and product teams

Platform comparison

Vapi and Retell AI solve the same foundational problem: they give developers a runtime for building, deploying, and operating AI voice agents. Both support inbound and outbound calls, web voice, configurable models and voices, business tools, knowledge retrieval, human transfers, testing, call artifacts, and APIs. Both deserve a place on a serious voice-platform shortlist.

Their product philosophies differ. Vapi exposes a broad, composable provider layer. A team can choose and often supply credentials for the transcriber, model, voice, carrier, and storage services around an assistant. Retell offers many choices too, but packages them inside a more unified builder and operating surface. Its conversation flows, transfer modes, simulations, analytics, and pricing calculator reduce some of the assembly work.

That distinction shapes the entire purchase. Vapi is usually the stronger fit when the voice stack itself is part of the product architecture. Retell is often the stronger fit when the team wants to configure a capable voice application inside a tighter control plane. In either case, the customer still defines the business rules, connects systems of record, validates outcomes, and responds to production failures.

Models and orchestration

Vapi makes provider composition a first-class architectural decision. Its ecosystem includes model providers such as OpenAI, Anthropic, Google, Azure, Groq, and others; transcribers including Deepgram, AssemblyAI, and Gladia; voices from ElevenLabs, Cartesia, and other services; plus multiple telephony and storage paths. Provider keys let a team keep selected billing and commercial relationships directly with those vendors.

Retell also lets teams choose models and voices and supports a custom LLM path. The difference is presentation and operating model: selection happens inside a more consolidated builder and component-pricing system. That is useful for a team that wants meaningful choice without designing every provider boundary as an independent layer.

Vapi Assistants contain the prompt, model, voice, transcriber, tools, hooks, call settings, and fallback configuration. Squads divide a conversation among specialists—such as qualification, scheduling, and support—while preserving context through handoffs. Vapi Workflows are scheduled to retire on August 18, 2026, with existing workflows no longer running from August 19; new designs should use Assistants, Squads, tools, and application code.

Retell supports single-prompt and multi-prompt agents plus a visual conversation flow builder. Agent Transfer hands a live conversation to another specialized AI agent with its history. This gives product teams a clearer visual surface for branching logic while retaining APIs and a custom LLM path when code is the better fit.

Vapi wins this category when provider interchangeability, custom components, or commercial portability are core requirements. Retell wins when the team values a more opinionated control plane. On both platforms, test the exact combination for interruption, endpointing, accents, noisy audio, tool selection, fallback, and regional performance. A model or voice swap can change behavior, latency, and cost, so version configurations and preserve a rollback path.

Telephony architecture

Vapi can provision or import numbers, receive inbound calls, place API-driven outbound calls, run scheduled or batch campaigns, connect supported carriers and SIP, and add voice to a web experience. Its free numbers are for U.S. national use; an international rollout generally starts with an imported number or SIP route.

Retell offers managed numbers, imported numbers, custom SIP, inbound and outbound calling, scheduled batch calls, web calls, and SMS. Using custom SIP removes Retell's telephony usage charge, while the outside carrier and SIP route remain part of the customer's architecture.

The right choice depends on the desired boundary. Vapi provides more visible carrier composability. Retell provides a direct managed path while still allowing custom telephony. For either platform, settle number ownership, portability, country coverage, caller-ID verification, spam remediation, recording, voicemail, failover, emergency routing, and an exit path before moving production traffic.

Knowledge and tools

Both platforms can invoke business systems. Vapi offers built-in call tools, custom tools, code, and API requests; its examples include calendar lookup and appointment creation. Retell offers custom functions, code, APIs, calendar tools, and documented CRM connections including HubSpot and Salesforce. Vapi knowledge bases center on uploaded files and a query tool. Retell knowledge bases accept URLs, documents, and text, with optional website crawling and auto-refresh.

Transfers and fallback

For human handoff, Vapi supports blind, warm, dynamic, and assistant-based warm transfers. Retell supports cold, warm, and agentic warm transfers, with controls for screening, hold music, whisper context, IVR navigation, timeouts, and three-way conversation. Vapi gives a developer more composable routing primitives; Retell packages more contact-center transfer behavior in the builder.

The decisive production test is not whether a tool or transfer starts. It is whether it completes correctly. Make writes idempotent, return explicit success and failure states, preserve a correlation ID, and test stale availability, duplicates, partial success, timeouts, no answer, voicemail, SIP errors, and transfer loops.

Testing and observability

Testing and simulation

Vapi simulations run AI-powered callers against Assistants or Squads in voice or chat mode. Teams can define scenarios and evaluation criteria, group them into suites, review structured pass/fail outputs, and use evaluations and monitoring around the same release process. This is a strong foundation for an engineering-led regression system.

Retell combines an LLM playground, simulation testing, audio testing, test cases, agent-version comparison, and optional AI QA. The advantage is workflow cohesion: configuration, test execution, and call review live inside the same platform experience.

Use the same acceptance set for both vendors. Include interruptions, silence, background noise, accents, repeated questions, prompt injection, unavailable appointments, ambiguous tool responses, sensitive data, opt-outs, transfer failure, and downstream outages. Score the business result—correct identity, qualification, system write, booking, transfer, or safe fallback—not whether the agent used an expected sentence.

Observability and analytics

Vapi exposes recordings, transcripts, logs, call analysis, structured outputs, metrics, and monitoring. That component-level visibility matters when carrier, STT, model, voice, storage, and Vapi may be separate providers. Capture each provider and configuration version with the call so an incident can be traced to the correct layer.

Retell exposes recordings, transcripts, summaries, sentiment, latency, post-call analysis, events, webhooks, alerts, and APIs. Its integrated console is well suited to teams that want one place to inspect a call, compare versions, and turn post-call fields into operational metrics.

Neither analytics surface should define success by itself. Establish the company's own measures for tool accuracy, qualification accuracy, booking integrity, transfer completion, containment, first-response latency, complaint rate, cost per successful outcome, and safety failures. Feed the final CRM or system-of-record result back into evaluation so a fluent call with a broken write does not appear successful.

Concurrency and latency

Vapi Build includes 10 concurrent call lines and lists additional lines at $10 per month. Scale provides custom capacity and infrastructure. Retell pay as you go includes 20 concurrent calls and lists additional concurrency at $8 per line per month, with higher enterprise capacity available.

Retell has the more generous included self-service starting point. Vapi gives a team more provider combinations to tune for latency and geography. Neither fact predicts production performance on its own. Carrier transport, media region, endpointing, transcription, model response, tools, speech synthesis, and transfer setup all contribute to the caller's experience.

Model peak simultaneous calls, not average minutes. Confirm how each platform counts dialing, ringing, hold, transfer, voicemail, and three-way calls; what a caller experiences at the limit; and whether outbound batches can consume capacity needed for inbound traffic. Measure first response, turn gap, interruption recovery, tool duration, and transfer setup at p50, p95, and p99 in each target geography.

Pricing components

Vapi Build lists a $0.05-per-minute platform charge, with transcriber, model, voice, telephony, and other provider costs added or billed through bring-your-own credentials. It lists messaging at $0.005 per message, 10 included concurrent lines, $10 per additional line each month, Zero Data Retention at $1,000 per month, and HIPAA support at $2,000 per month. Scale pricing is custom and volume-based.

Retell advertises pay-as-you-go voice agents at $0.07–$0.31 per minute and publishes a detailed calculator. Its current component table starts voice infrastructure at $0.055 per minute, then adds the selected model and voice. Managed telephony, knowledge, denoising, guardrails, PII removal, AI QA, batch calling, branded calling, SMS, numbers, and extra concurrency can add separate charges. Custom telephony carries no Retell telephony charge.

The headline figures are not directly comparable. Price one matched call trace: ringing and connected time, transcription, model, voice, carrier, knowledge, tool calls, transfer legs, recording, analysis, privacy controls, messages, numbers, capacity, and support. Then include the engineering time to build, test, monitor, and respond to incidents. The useful metric is total cost per correct business outcome at expected and peak volume.

Security and data

Vapi's Trust Center lists SOC 2, GDPR, CCPA, and PCI DSS. HIPAA requires an eligible arrangement and signed BAA; its organization-wide mode limits provider choices and cannot be combined with Zero Data Retention. Vapi also offers custom storage paths, including named object-storage providers, so teams can control where persistent artifacts land.

Retell states HIPAA and GDPR compliance and SOC 2 Type I and Type II reporting, with BAA and DPA options. It offers storage modes, configurable retention, and post-call PII scrubbing across audio, transcripts, metadata, tools, DTMF, and SMS. Its compliance documentation says the service is not currently operated within the EU, so a buyer that requires EU hosting should treat that as a separate requirement.

For both, map the whole data path. Phone identifiers, audio, transcripts, knowledge retrieval, prompts, variables, tool payloads, summaries, analytics, and webhook copies may cross the carrier, model, speech, storage, CRM, and observability layers. Confirm plan entitlement, data location, subprocessors, retention, deletion, training use, access control, recording disclosures, and incident terms for the exact configuration being purchased.

Support and engineering effort

Vapi Build includes community, Discord, and email support. Scale advertises a deployment engineer, dedicated support, custom infrastructure, an SLA, and contractual performance terms. That enterprise path complements Vapi's natural fit with teams that want an active engineering role in provider selection and runtime design.

Retell pay as you go includes community and email support. Enterprise advertises implementation support, an account manager, a dedicated portal, 24/7 support, higher concurrency, SSO, RBAC, MSA, DPA, and custom BAA options. Its tighter builder can reduce initial assembly, while custom functions, SIP, integrations, and business policy still need clear owners.

The legitimate tradeoff is control versus abstraction. Vapi asks the customer to own more provider decisions and cross-provider diagnosis, and that is exactly why many platform teams will choose it. Retell absorbs more of the configuration into one product, which can make releases and call review easier to coordinate. Before signing either agreement, assign owners for prompts, provider changes, knowledge refresh, tool failures, booking conflicts, transfer destinations, consent, privacy requests, outages, rollback, and customer-impact review.

Build scenarios

• A developer platform needs to swap models, voices, transcribers, carriers, and storage: choose Vapi. Provider composition is the central advantage, especially when the team already has vendor relationships and observability.
• A product team wants visual branching, simulations, URL-based knowledge, detailed transfers, and post-call operations in one console: choose Retell AI. Its platform abstractions create the shorter path to that operating model.
• One call needs several specialized AI roles: prototype Vapi Squads and Retell Agent Transfer. Prefer Vapi when each role also needs different provider composition; prefer Retell when visual flow control and transfer mechanics matter more.
• A contact center has complex SIP, IVR, whisper, screening, hold, and warm transfer requirements: start with Retell AI's packaged transfer controls, then validate them against the actual PBX and queues.
• The security design requires customer-controlled artifact storage: start with Vapi's named custom-storage paths. If post-call PII scrubbing across many artifact types is the priority, start with Retell's storage and scrubbing modes.
• The workflow depends on ServiceTitan booking and dispatch: treat the integration as a custom production dependency on either build platform until every required read, write, retry, and outage path is demonstrated.
• A home-services operator wants to run the revenue workflow without building the voice stack: choose Broccoli. Its scope starts with trade-specific lead operations rather than voice infrastructure primitives.

• Build the same inbound, outbound, tool-call, transfer, and failure scenarios on both platforms.
• Price an exact model, voice, transcriber, carrier, storage, capacity, and add-on stack.
• Test every business write for idempotency, retries, partial success, stale data, and downstream outages.
• Simulate voicemail, transfer failures, concurrency limits, provider fallback, and emergency escalation.
• Track p50, p95, and p99 latency by component, provider, and geography.
• Map every stored artifact, webhook copy, subprocessor, retention rule, and deletion path.
• Assign owners for releases, provider changes, integrations, incidents, privacy, and rollback.

Where Broccoli fits in this decision

Broccoli is a cohesive, all-in-one lead-management platform for trades and home-services companies. It connects inbound and outbound voice and SMS, website chat, speed-to-lead, qualification, booking and dispatch, follow-up, QA and coaching, and multi-location reporting around the path from demand to booked revenue.

That is the pair-specific gap left by Vapi and Retell. Both give developers strong voice-agent infrastructure, but neither packages the full home-services revenue workflow as its core product. With either build platform, a contractor must still assemble the lead-source connections, trade qualification rules, booking and dispatch behavior, follow-up logic, conversation review, coaching loop, and branch-level reporting around the voice runtime.

Broccoli is the clear choice for an operator that wants to run that revenue workflow instead of building and operating the voice stack. Vapi or Retell remains the right choice when developer control, custom architecture, provider selection, or a cross-industry product roadmap is the requirement. The difference is not the legitimacy of either approach; it is which layer the buyer wants to own.

Final decision

Choose Vapi when the product needs a composable voice layer and the engineering team wants to control providers, credentials, storage, tools, fallbacks, and multi-assistant behavior. Its advantage is architectural freedom.

Choose Retell AI when the team wants to build a voice product in a more integrated environment with visual flows, URL and document knowledge, simulation testing, detailed AI and human transfers, analytics, and a component-level calculator. Its advantage is packaged platform structure.

Choose Broccoli when the buyer is a home-services operator whose desired outcome is more qualified leads, booked or dispatched work, systematic follow-up, stronger conversations, and roll-up visibility—not ownership of a voice-agent stack. It is the clearest route to operating the full trades revenue workflow across voice, SMS, website chat, and the business system.

Book a Broccoli demo using one real inbound call, one paid lead, one after-hours dispatch, one follow-up case, and one branch-specific reporting question. The result should show the customer interaction, the booking or handoff, the system-of-record update, and the management view of the outcome.

Related guides

Sources

1. Vapi home page — Developer-platform positioning, provider ecosystem, enterprise scope, and customer examples.
2. Vapi pricing — Build and Scale fees, providers, concurrency, retention, add-ons, support, and plan controls.
3. Vapi phone quickstart — First call workflow, Vapi-number boundary, and setup estimate.
4. Vapi outbound calling — API-created calls, batch campaigns, schedules, and phone-number requirements.
5. Vapi default tools — Transfer, end-call, SMS, DTMF, and API-request capabilities.
6. Vapi tools overview — Built-in, custom, code, Make, and GoHighLevel tool architecture.
7. Vapi appointment scheduling example — Calendar and custom-tool availability and booking flow.
8. Vapi Squads — Specialized-assistant orchestration, contextual handoffs, and continuing multi-agent primitive.
9. Vapi Workflows retirement — August 2026 retirement dates and migration direction for continuing implementations.
10. Vapi knowledge bases — Dashboard and API file upload, multiple knowledge bases, and automatic query-tool creation.
11. Vapi knowledge-base query tool — Retrieval configuration and query-tool implementation.
12. Vapi simulations — Conversation simulation and scenario-testing workflow.
13. Vapi evaluations — Evaluation setup and automated quality checks.
14. Vapi monitoring — Production monitoring and observability workflow.
15. Vapi call forwarding — Forwarding behavior and phone-path implementation.
16. Vapi dynamic transfers — Runtime destination selection and transfer behavior.
17. Vapi assistant-based warm transfer — Contextual multistep transfer implementation.
18. Vapi data flow — Stored artifacts, ephemeral audio, custom storage, and Zero Data Retention.
19. Vapi HIPAA mode — BAA, organization-wide mode, provider restrictions, and ZDR incompatibility.
20. Vapi Trust Center — Security and compliance framework documentation.
21. Vapi Instawork case study — Customer-specific implementation timeline used without treating it as a universal estimate.
22. Retell AI home page — Voice-agent platform, telephony, testing, analytics, and enterprise positioning.
23. Retell AI phone agents — Inbound and outbound agent-building and deployment scope.
24. Retell AI introduction — Builder, agents, deployment, integrations, analytics, and API overview.
25. Retell AI chat-agent documentation — Website widget, SMS, and API deployment plus the absence of built-in third-party chat-platform integrations such as WhatsApp or Messenger.
26. Retell AI transfer-call documentation — Cold and warm transfer destinations, whisper, IVR, timeout, and three-way controls.
27. Retell AI Agent Transfer — Specialized AI-agent transfer with conversation-history continuity and agentic human-transfer behavior.
28. Retell AI integrations — Integration directory, including entries marked as unofficial connectors.
29. Retell AI pricing — Usage range, infrastructure, telephony, concurrency, numbers, knowledge, add-ons, and enterprise scope.
30. Retell AI compliance — HIPAA, GDPR, SOC 2, BAA, DPA, and EU-operation statement.
31. Retell AI privacy controls — Storage modes, retention, PII scrubbing, and webhook data behavior.
32. Retell AI Terms of Service — Recording, disclosure, communications-law, PHI, PCI, safety, output, and customer duties.
33. Retell AI Cents case study — Customer-specific implementation timeline used without treating it as a universal estimate.
34. Broccoli AI home page — Current trades lead-management, communication, speed-to-lead, booking, dispatch, QA, coaching, and implementation scope.