Sierra AI Review 2026: Pricing, Features and Verdict

What it is

Sierra is a conversational AI platform for businesses, used mainly by large consumer brands to run customer facing AI agents for service, retention and sales. It was co founded by Bret Taylor, former co CEO of Salesforce, founder of Quip, former CTO of Facebook and chair of OpenAI's board, and Clay Bavor, who led Google Labs, Project Starline and Google Lens over 18 years at Google. Sierra has offices in San Francisco, New York, Atlanta, London, Singapore, Tokyo, Paris, Madrid and Toronto.

Sierra goes beyond answering questions. Its pitch is an agent that remembers customers across channels and systems, plans multi step outcomes over days or weeks (Horizon), triggers proactive outreach and is optimized for satisfaction and revenue within your guardrails.

Like Decagon, it is not a helpdesk. It connects to your systems of record and hands off to your human team.

Pricing explained

Sierra publishes no prices. Its stated model is outcome based pricing:

• You pay when the agent completes an agreed outcome
• Outcomes can be a resolved support conversation, a saved cancellation, an upsell, a cross sell or a purchase
• If the conversation is unresolved, in most cases there is no charge
• Rates and outcome definitions are set in your contract

Sierra's argument is that this aligns incentives: it earns more only when its agent does more useful work, so it keeps optimizing after launch. Its newer Horizon agents extend the same model to multi day journeys: "you pay for results, not tokens."

The risk is in the definitions. What counts as resolved, how long a customer must stay quiet, whether a saved cancellation that churns next month still counts: all of that is negotiated. Ask for the exact outcome definitions and verification method in writing, and compare against published rates such as Intercom Fin at $0.99 per outcome or Zendesk at $1.50 committed per LLM verified resolution. All tracked prices are on the AI Price Index.

Key features

Ghostwriter and Agent Studio

Ghostwriter is what Sierra calls the agent building agent. You upload SOPs, call transcripts, whiteboard photos or audio recordings, or describe the goal in plain English, and Ghostwriter builds a multilingual, multichannel agent with guardrails. It then proposes updates based on flagged issues and insights, with every change visible for review. Agent Studio lets non engineers build and edit agents, and the Agent SDK gives engineering teams code level control.

Channels

One agent runs across:

• Voice: inbound and outbound, low latency, handles interruptions, noise and accents, and adapts tone to sentiment. Voice Personas set how the agent sounds across 60+ locales.
• Messaging: website, mobile app, WhatsApp, Apple Business Chat and SMS, with images and video in messages.
• Email: autonomous replies using CRM data and account context.
• ChatGPT: publish the same agent as a ChatGPT app through MCP, choosing which journeys and data to expose.
• Live Assist: suggested replies and one click actions for human care reps, from the same agent.

Sierra lists 58 languages across channels.

Horizon and the Context Engine

Horizon breaks complex outcomes into steps that run over days or months, combining inbound and outbound interactions. The Context Engine gives the agent memory across conversations, systems and touchpoints. Outcome optimization personalizes decisions to maximize satisfaction and revenue within your rules, and proactive engagement triggers next best actions from real world signals.

Insights and quality

Explorer runs deep research style analysis over conversations. Monitors flag conversations that need attention. Experiments run multivariate tests on conversation design. Observability shows every tool call, knowledge lookup and latency figure. Sierra also publishes agent benchmarks, including tau voice, which scores real time voice agents on 278 customer service tasks across retail, airline and telecom.

Payments

Sierra's payment infrastructure keeps cardholder data on dedicated PCI certified infrastructure that never touches its core platform, LLMs or storage. Sierra holds PCI DSS Level 1 Service Provider certification and says customers complete thousands of card and ACH transactions a day across voice and chat.

Model strategy

Sierra uses a constellation of frontier, open weight and proprietary models, choosing different models for decisions, understanding messages and generating responses, and switches LLM providers automatically if one has an outage. Supervisor models wrap the LLMs to reduce hallucinations and block abuse.

What users say

Sierra does not have a public review base large enough to rate on the sites we checked; its buyers are large enterprises that rarely post on G2 or Trustpilot. The evidence available is customer quotes on Sierra's site. Clear's VP of member experience describes the agent as augmentation, with humans always available. Casper's VP of operations points to 24/7 availability in any language. Minted stresses accuracy on personal orders. Singtel Singapore's CEO highlights agents that understand local expressions including Singlish. Ask for references in your industry and for resolution data from comparable deployments.

Privacy and security

Sierra's trust page lists SOC 2, HIPAA, GDPR, PCI, FedRAMP High, CCPA, CSA STAR, ISO 27001 and ISO 42001, the broadest list among the AI agent vendors we track. FedRAMP High matters for public sector buyers, and ISO 42001 is an audited AI management standard.

On data, Sierra says your data is used only as you instruct and is never shared with other customers, PII is automatically encrypted and masked, and agent access to your systems of record is deterministic and controlled to follow your policies. Built in filters and monitors block off limits topics. Detailed controls and security documents are available through its trust center.

Who it is for

• Large consumer brands in retail, travel, media, telecom and technology
• Regulated industries, including financial services, healthcare and public sector, that need FedRAMP High, HIPAA or PCI DSS Level 1
• Companies that want AI to drive retention and revenue, not only deflection
• Teams that want to pay per outcome and can negotiate outcome definitions

Who should skip it

• Small and mid size businesses; there is no self serve plan or published price
• Teams that want a fixed published rate card; see Fin or HubSpot Customer Agent
• Buyers looking for a helpdesk; Sierra sits on top of one
• Anyone who needs to be live in a week without vendor involvement

Alternatives

• Decagon: the closest rival, with plain language AOPs and per conversation pricing; see Decagon vs Sierra
• Intercom Fin: published $0.99 per outcome; see Intercom Fin vs Sierra
• Ada: enterprise AI agent across voice and digital channels
• Salesforce Agentforce: if your service team runs on Salesforce

Verdict

Sierra is a top tier choice for enterprises that weigh compliance, voice quality and pricing alignment above speed and transparency. Its certification list, PCI Level 1 payments, ChatGPT channel and Horizon long running agents are ahead of most rivals on paper, and outcome based pricing puts the vendor's revenue on the line. The cost is opacity: no published prices, negotiated outcome definitions and no public review base. Shortlist it next to Decagon, demand written outcome definitions, and benchmark every quote against published per resolution rates.