Retell AI vs Sierra AI (2026)
Comparing Retell AI and Sierra AI? Both are AI Agents & Chatbots and Voice & Phone AI tools in the directory, which is why buyers put them on the same shortlist. Below is a side-by-side look at pricing and an estimated monthly bill, channels, compliance claims, and integrations, plus when each is the better fit, so you can pick on the facts rather than either vendor's own sales page.
At a glance
| Attribute |
 Retell AI
|
 Sierra AI
|
|---|---|---|
| What it is | Self-serve platform for building, testing, and monitoring AI phone agents, priced per minute with published component costs. | AI agent mirrors the nuances of human communication, ensuring seamless and organic customer service interactions while improving customer satisfaction. |
| Pricing | Paid · $0.07/min | Per resolution · Custom |
| Est. monthly cost | $840/mo $0.07 per minute | No published price to estimate |
| Founded | 2023 | 2023 |
| Categories | AI Agents & Chatbots Voice & Phone AI | AI Agents & Chatbots Enterprise Voice & Phone AI |
| Channels | ||
| Chat | ✓ | ✓ |
| — | ✓ | |
| Voice | ✓ | ✓ |
| SMS | ✓ | ✓ |
| — | ✓ | |
| Compliance (vendor-claimed) | ||
| SOC 2 | ✓ | ✓ |
| HIPAA | ✓ | ✓ |
| GDPR | ✓ | ✓ |
| ISO 27001 | ✓ | ✓ |
| PCI DSS | — | ✓ |
| FedRAMP | — | ✓ |
| ISO 42001 | — | ✓ |
| EU AI Act | — | ✓ |
| Data residency | US | Not verified |
| Languages | 55 languages | 59 languages |
| What the AI can do | ||
| Takes actions | ✓ | ✓ |
| Hands off to a human | ✓ | ✓ |
| Choice of LLM | ✓ | — |
| Buying | ||
| Free trial | Free credits ($10) on pay-as-you-go | Not verified |
| How you buy | Self-serve signup | Not verified |
| Minimum commitment | No minimum, no contract (pay as you go) | — |
| Company | Independent, venture-backed | Independent, venture-backed |
| Works with | Twilio Vonage Telnyx Cal.com n8n Make GoHighLevel HubSpot | Salesforce Zendesk Shopify Twilio Stripe Snowflake |
| Key features |
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| Next step |
Full listing Visit site → |
Full listing Visit site → |
Estimates assume 5,000 conversations a month, 60% handled by AI and 10 agent seats, at each vendor's published list price (the cost calculator's model); treat them as a floor, not a quote. Compliance rows are what vendors publicly claim, and “Not verified” means we have not confirmed that fact yet, not that the tool lacks it.
Choose Retell AI or Sierra AI?
Choose Retell AI if
Best for: Developers and operations teams that want to build their own AI phone agents from interchangeable speech, LLM, voice and telephony parts, with published per-minute pricing from $0.07, free starting credits, 55 languages, US hosting and SOC 2, HIPAA and GDPR coverage.
- you prefer a flat subscription to usage-based billing
Look elsewhere if you want a finished support agent or a help desk integration out of the box: Retell is a builder's platform, and its verified integrations are telephony, automation and scheduling tools rather than ticketing systems.
Choose Sierra AI if
Best for: Large brands that want one branded agent deployed across chat, voice, email, SMS and WhatsApp, with voice agents that can take a payment mid-call, outcome-based pricing, 59 languages and the broadest compliance list in the directory including FedRAMP, ISO 42001 and the EU AI Act.
- you need enterprise scale, security, and compliance
- you need Email and WhatsApp coverage
- you need a vendor that publicly claims PCI DSS, FedRAMP, and ISO 42001
- you would rather pay per resolved ticket than per seat
Look elsewhere if you are not an enterprise: Sierra sells multi-year contracts by quote with no trial or self-serve start, and its verified facts do not include a stated data residency.
About Retell AI
Retell AI is a platform for building AI phone agents that answer and place calls. You compose an agent from interchangeable parts: a speech-to-text layer, your choice of LLM, a voice from providers like ElevenLabs, and telephony via Twilio, Vonage, Telnyx, or your own SIP trunk. The platform handles the hard real time bits, interruption handling, latency, call transfer, and IVR navigation, and adds testing, monitoring, and post call analysis aimed squarely at contact center and front desk workloads.
The company came out of Y Combinator's Winter 2024 batch, founded in 2023, with Evie Wang among the cofounders. It grew unusually fast for a seed stage company: a $4.6 million seed led by Alt Capital in September 2024 arrived alongside a reported $3 million in annual revenue within months of launch. Named customers include telehealth company Ro, plus BPOs and contact center operators.
Pricing is published and usage based, which is refreshingly rare. Retell quotes $0.07 to $0.31 per minute all in, depending on your voice and model choices, with components itemized: text-to-speech from $0.015 per minute, LLM costs from $0.003 to $0.16 per minute, US telephony around $0.015 per minute. Every account includes 20 concurrent calls, extra concurrency is $8 per line monthly, phone numbers cost $2 monthly, and new accounts get $10 in free credits. Enterprise plans with dedicated infrastructure are custom.
Choose Retell if you have some technical ability, want a working phone agent this week, and value published per minute economics you can model before committing. Its contact center tilt (batch calling, warm transfer, IVR traversal) makes it a natural fit for support lines. Look elsewhere if you want a fully managed enterprise deployment with a vendor doing the tuning, or a pure no-code experience for a non-technical team.
Read the full Retell AI listing → · See Retell AI alternatives →
About Sierra AI
Sierra builds conversational AI agents for the enterprise, and it arrived with about as much star power as a startup can carry. It was founded in 2023 by Bret Taylor and Clay Bavor, and if those names ring a bell it is because Taylor co-created Google Maps, served as CTO of Facebook and co-CEO of Salesforce, and currently chairs the board of OpenAI, while Bavor spent eighteen years at Google leading its virtual and augmented reality work. Company lore says the whole thing was hatched over a grilled branzino lunch in Palo Alto.
The product lives up to the pedigree. From a single build, Sierra deploys a branded agent across chat, voice, email, SMS, and even ChatGPT, following your policies, adopting your brand's voice, and escalating gracefully when a conversation gets thorny. Its voice agents are a standout: they hold natural, low-latency conversations, read sentiment, and can even take a credit card or ACH payment over the phone in one uninterrupted call, with no clumsy handoff to a separate system.
Under the hood sits Agent OS, a platform for building, testing, and supervising agents, with tooling to run voice simulations and rehearse behavior before anything reaches a real customer. Pricing is outcome-based, tied to conversations or successful resolutions and wrapped in multi-year enterprise contracts, so Sierra is aimed at large brands rather than weekend experimenters. Reported customers include SoFi, Ramp, and Brex, and the company says its agents already serve a meaningful slice of the Fortune 50.
Sierra's fundraising has kept pace with its towering ambition, vaulting the company into the rarefied tier of the most valuable AI startups in barely two years. For enterprises that want polished, on-brand agents across every channel and are willing to invest the time and budget to do it properly, Sierra is a genuine marquee choice.
Read the full Sierra AI listing → · See Sierra AI alternatives →
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