PolyAI vs Sierra
A side-by-side comparison of PolyAI and Sierra on what each one charges, what it meters, and which plan every capability actually sits on.
Capability by capability
Nothing we track differs between them.
Channels
| Capability | PolyAI | Sierra |
|---|---|---|
| Not published | IncludedNo plans are published, so plan gating cannot be assessed. | |
| Live chat | Not published | IncludedNo plans are published, so plan gating cannot be assessed. |
| Voice | IncludedThe only channel. Calls arrive over a SIP or PSTN integration into the customer's existing CCaaS platform or telephony provider. | IncludedNo plans are published, so plan gating cannot be assessed. |
| Not published | IncludedNo plans are published, so plan gating cannot be assessed. |
AI resolution
| Capability | PolyAI | Sierra |
|---|---|---|
| Autonomous resolution agent | Not published | IncludedThe whole product. Sierra bills only on outcomes such as "a resolved support conversation", which presupposes autonomous resolution. |
| Action-taking (API calls) | Included"Other systems can be integrated via APIs", with an Agent Developer Kit for custom functions and flow control, and a Connect Portal handling OAuth 2.0 and field mapping. Card payments are taken through a documented PCI Pal integration. | Included"Enable your agent to take action to assist customers by securely connecting it with any internal or external system", including systems of record from order management to CRM. |
| Handoff to human | Not published | IncludedEscalation exists and is usually not billed: "if a case needs to be escalated, in most cases, there's no charge". The exceptions are unpublished. |
| Guardrails & citations | Not published | IncludedGuardrails are published as "supervisory layers to reduce hallucinations, ensure security, and prevent abuse", and PII is "automatically encrypted and masked". Citation behaviour is not addressed anywhere, so half of this attribute is Unknown. |
| Multilingual AI | IncludedPublished counts conflict: 75 languages on the about page, 45 as standard on the technology page FAQ, and 43 individually named on the languages page under a 75+ title. | IncludedSierra publishes "voice, chat, email, and WhatsApp in 59 languages", available 24/7/365. |
AI voice
| Capability | PolyAI | Sierra |
|---|---|---|
| Voice agent | IncludedThe entire product. PolyAI describes itself as an Agentic Dialog Platform answering inbound calls for enterprise contact centres. | IncludedVoice is listed as a first-class agent channel alongside chat, email and WhatsApp. No per-minute rate or telephony passthrough is published. |
Enterprise
| Capability | PolyAI | Sierra |
|---|---|---|
| HIPAA / BAA | Not publishedHedged rather than certified: "Where relevant, our systems are designed to meet HIPAA requirements." No attestation and no BAA offer is published, and healthcare is a named vertical. | IncludedNot assessable; no plans are published. |
| SOC 2 | IncludedNone stated. No plans are published, so plan gating cannot be assessed either way. | IncludedNot assessable; no plans are published. |
| ISO 27001 | IncludedNone stated. No plans are published. | IncludedNot assessable; no plans are published. |
| GDPR | IncludedNone stated. No plans are published. | IncludedNot assessable; no plans are published. |
Developer
| Capability | PolyAI | Sierra |
|---|---|---|
| REST API | IncludedOpen APIs and an Agent Developer Kit are published as product surfaces. No public API reference and no data-export endpoint is documented, so what the API can read out is Unknown. | Not publishedNo public API reference is published on sierra.ai. The Agent SDK page describes extensibility without documenting an API. |
| SDKs | IncludedThe Agent Developer Kit is published as the programmatic control surface, documented at docs.poly.ai. | IncludedThe Agent SDK is a published product surface, described as extensible so customers can write and connect their own integrations. No public API reference is published. |
Both entries last checked Sep 9, 2026.
What PolyAI costs
- Billing unit
Per minute of voice agent use - Free tier
Not published - AI pricing
Not published - Vendor calls it
minute - Human handoff
Not published - Reopened chat
Not published - AI billing window
Not published - Data export
Not published - Automation export
Not published
7 of 9 not published by PolyAI, checked
What Sierra costs
- Billing unit
Per outcome - Free tier
Not published - AI pricing
Not published - Vendor calls it
Outcome - Human handoff
Not published - Reopened chat
Not published - AI billing window
Not published - Data export
Not published - Automation export
Not published
7 of 9 not published by Sierra, checked