PolyAI vs Sierra AI (2026)
Comparing PolyAI and Sierra AI? Both are Enterprise 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 |
 PolyAI
|
 Sierra AI
|
|---|---|---|
| What it is | Voice AI agents that sound human and resolve calls for enterprises: no hold time, 24/7. | AI agent mirrors the nuances of human communication, ensuring seamless and organic customer service interactions while improving customer satisfaction. |
| Pricing | Paid · Custom (per-minute) | Per resolution · Custom |
| Est. monthly cost | No published price to estimate | No published price to estimate |
| Founded | 2017 | 2023 |
| Categories | Contact Center & CCaaS Enterprise 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, UK, EU, APAC | Not verified |
| Languages | 75 languages | 59 languages |
| What the AI can do | ||
| Takes actions | ✓ | ✓ |
| Hands off to a human | ✓ | ✓ |
| Choice of LLM | Not verified | — |
| Buying | ||
| Free trial | Free signup; build your first agent free | Not verified |
| How you buy | Self-serve signup | Not verified |
| Minimum commitment | — | — |
| Company | Independent, venture-backed | Independent, venture-backed |
| Works with | Salesforce HubSpot Zendesk Microsoft Dynamics 365 OpenTable Zapier | 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 PolyAI or Sierra AI?
Choose PolyAI if
Best for: Enterprises in hospitality, banking, utilities and other high-call-volume sectors that want voice agents that sound human, survive interruptions and accents, and can take payments or health information on the phone, with SOC 2, HIPAA, PCI DSS, GDPR and ISO 27001 coverage, 75+ languages and a free build-your-first-agent signup.
- you prefer a flat subscription to usage-based billing
Look elsewhere if your support is chat and email: PolyAI is voice-only. Pricing is per minute by quote, and its verified facts do not include a stated data residency.
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 autonomous AI agents
- you need Email and WhatsApp coverage
- you need a vendor that publicly claims FedRAMP, ISO 42001, and EU AI Act
- 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 PolyAI
PolyAI answers the phone. While most of this directory started with chat and added voice later, PolyAI has been voice-first since three Cambridge machine-learning PhDs, Nikola Mrkšić, Pei-Hao Su, and Tsung-Hsien Wen, founded it in London in 2017 out of the university's Machine Intelligence Lab. Its agents are known for sounding genuinely human and for surviving the things that break lesser systems: interruptions, accents, background noise, and callers who change their mind mid-sentence. Restaurants, hotels, banks, and utilities use it to answer every call instantly, day and night, with customers like PG&E, UniCredit, Golden Nugget, and Fogo de Chao on the roster.
The platform matured into what the company calls an agentic dialog platform: Dialog Studio (formerly Agent Studio) for building and managing agents without code, a developer kit for deeper work, and its own dialog models: the audio-native Dialog-RSN-1 for calls and Raven, trained on more than a billion enterprise conversations, for webchat and multilingual text. Inside Dialog Studio sits Wren, an agent that builds agents from a description, reviews production calls on a schedule, and drafts and tests fixes that wait for a person to approve them. Compliance boxes (SOC 2, HIPAA, PCI) are ticked, which matters because taking payments and health information over the phone is exactly where voice AI earns its keep.
Investors have noticed the wedge. In December 2025 PolyAI raised an $86 million Series D at a valuation around $750 million, with NVIDIA's venture arm participating, bringing total funding past $200 million. Commercially it bills on usage, priced per minute of conversation, with rates scoped to your call volume rather than published on the site.
Choose PolyAI when the phone is your problem. If most of your support pain is hold music, missed calls, and staffing the night shift, a voice-native specialist will beat a chat-first platform's bolted-on telephony, and PolyAI is one of the most proven voice specialists in the market.
Read the full PolyAI listing → · See PolyAI 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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