12 Best Sierra AI Alternatives in 2026: Ranked and Compared

Quick Summary

Callers leads this list for teams that run inbound and outbound at scale across voice and messaging. Decagon, Ada, and Zowie suit digital support automation. PolyAI, Cognigy, Parloa, and Five9 fit enterprise contact centers. Voiceflow, Retell, and Synthflow are for teams that'd rather build their own.

Looking for a Sierra AI Alternative?

Sierra builds polished AI agents for big brands. But its outcome-based pricing stays behind a quote, and standing up a new Agent OS takes time. If that gives you pause, it's worth seeing what else is out there.

Sierra does a lot well. It runs one agent across chat, voice, email, and more, and its Ghostwriter tool spins up agents fast. For large teams standardizing on a single platform, that's appealing. Still, plenty of other omnichannel AI agent platforms solve the same problems in different ways.

The reason people shop around is fit. Some teams want clear pricing they can budget. Some want to keep the contact center they already run. Others care most about outbound calling or step-level analytics. This guide walks through 12 strong options so you can match the tool to the job.

Why Listen to Us?

DoorDash, Einride, and PadSplit run live customer conversations on Callers. It runs one agent across phone, SMS, WhatsApp, email, and chat from a single shared context layer, covering sales, support, and retention for high-volume B2C.

Callers was engineered with Google Cloud, and that partnership shows under load. The platform scaled 30X and now carries hundreds of thousands of AI conversations every day without call quality slipping.

The Callers case studies go deeper.

Why Look for Sierra AI Alternatives?

Sierra is a strong product, so the reasons to compare are about fit and model, not quality.

Pricing is quote-only

Sierra uses outcome-based pricing, and it's not published. You request a quote to see numbers. That works for some buyers, but it makes early budgeting hard. Many teams want a clear per-minute or per-seat rate before they commit.

It's a platform to adopt

Sierra positions its Agent OS as the system of record for customer conversations. That's a big commitment. If you already run a contact center, CRM, and telephony you like, you might prefer a tool that slots in rather than one you build your operation around.

Rollout can take time

Standing up a new agent platform means onboarding, integration, and tuning. A simple use case can move quickly, but complex setups take longer. Teams that need to be live in weeks sometimes want a faster path.

Analytics stay high-level

Sierra reports on resolution and outcomes well. What some teams miss is step-level detail, the view of exactly where a script or call drops off. Without that, it's harder to see which line lost the customer and fix it.

Built for very large brands

Sierra targets the biggest companies in the world, including a large share of the Fortune 50. If you're a mid-market B2C team, that focus can feel like more platform than you need, at a price to match.

The 12 Best Sierra AI Alternatives

1. Callers

Callers is an omnichannel AI platform for high-volume B2C teams. One agent handles phone, SMS, WhatsApp, email, and chat, carrying context across all of them. Inbound support and outbound campaigns both run as first-class jobs, so a customer picks up wherever they left off.

Where Sierra asks you to adopt a new Agent OS, Callers drops into the stack you already run and goes live in weeks. Your operators build and edit agents in a no-code builder, so you're not waiting on engineering, and step-level analytics show exactly where each call or script wins or loses.

When your team does want help, a dedicated customer success manager is included on every plan, bringing AI optimization and strategic planning advice, not just onboarding.

Key features

• Omnichannel one brain: one agent across voice, SMS, WhatsApp, email, and chat with shared context

• Workflow Orchestration: sequences, conditional retries, pre-call triggers, and post-call actions across inbound and outbound

• No-code Script Builder: drag-and-drop flows with AI-assisted scripting, owned by operators

• Step-level analytics: see where conversations break down and what to fix

• White-glove customer success: a dedicated CSM on every plan, providing AI optimization recommendations and strategic planning advice

• AI and human routing: simple work stays with AI, high-stakes calls warm-transfer to your team

• Compliance built in: SOC 2, HIPAA, GDPR, CCPA, and PCI DSS

Pricing

Custom, usage-based per minute. Pricing is set with your team based on volume, so you pay for what you use rather than per seat. Book a demo to get a quote.

Pros

• One agent across every channel, strong on inbound and outbound alike

• Live in weeks, no long platform migration

• Operators build and run agents without developers

• White-glove customer success on every plan, not just Enterprise

• Step-level analytics you can act on

• Fits your existing CCaaS, CRM, and telephony

Cons

• Pricing is demo-gated, so you request a quote to see rates

• Aimed at high-volume B2C, so very low-volume teams may not need it

Best for

High-volume B2C teams that want omnichannel automation across inbound and outbound without replacing their stack.

Why choose Callers over Sierra

Sierra wants to become your agent platform. Callers makes the operation you already run better and faster. It fits your current CCaaS, CRM, and telephony with no rip-and-replace, and it goes live in weeks.

You also get a dedicated customer success manager on every plan, so your team can lean on Callers' experience for both AI optimization and strategic planning, support that competitors usually reserve for their largest accounts.

2. Decagon

Decagon is an enterprise AI concierge platform that builds autonomous support agents for voice, chat, and email. Its Agent Operating Procedures let teams define workflows in plain language, which makes it one of the closest head-to-head options to Sierra.

Key features

• Omnichannel agents: one build deployed across voice, chat, and email

• Agent Operating Procedures: workflow logic written in natural language

• Voice AI: real-time interruption handling and outbound support

• Testing and QA: at-scale simulations and continuous quality monitoring

• Analytics: dashboards for deflection, CSAT, and cost

• Compliance: SOC 2 Type II and GDPR, with HIPAA eligibility on enterprise plans

Pricing

Custom, contact sales. Decagon doesn't publish pricing on its site, and it runs a usage-based enterprise model. Expect quote-only contracts sized to your volume.

Pros

• Strong autonomous resolution across channels

• Natural-language workflow design

• Deep testing and QA tooling

• Built for large consumer brands

• Solid compliance posture

Cons

• No public pricing

• Enterprise focus can be heavy for smaller teams

Best for

Large B2C support teams that want a highly configurable autonomous agent with strong testing tools.

Why choose Decagon over Sierra

If you're comparing concierge platforms directly, Decagon is the closest like-for-like. Its Agent Operating Procedures give you natural-language control, and its testing and QA tooling is a real strength for teams that iterate often. Pick Decagon over Sierra when autonomous digital resolution is your main goal.

3. Ada

Ada is an enterprise AI customer service platform whose autonomous agents resolve support requests end to end across messaging, voice, and email. Built for large support operations, it comes up often in head-to-head comparisons with Sierra and Decagon.

Key features

• Omnichannel agent: one agent across chat, voice, email, and social

• Unified Reasoning Engine: shared context, policies, and safeguards across channels

• Autonomous resolution: agents act on the customer's behalf and follow multi-step SOPs

• Multilingual: 60+ languages from one agent

• Integrations: connectors for Zendesk, Salesforce, Genesys, and more

• Compliance: SOC 2 Type II, HIPAA, GDPR, CCPA, and PCI

Pricing

Custom, contact sales. Ada publishes no prices and favors a conversation-based commitment model. It suits teams with very high volume, around 300,000 or more service conversations a year.

Pros

• High automated resolution rates at scale

• Wide language coverage

• Broad helpdesk integrations

• Strong safeguards against wrong actions

• Enterprise-grade compliance

Cons

• No public pricing

• Built for high volume, so a poor fit for smaller teams

Best for

Large enterprises with high-volume, multichannel support that want to automate a big share of contacts.

Why choose Ada over Sierra

Ada is proven at very high contact volumes, and it leans on a conversation-based commitment rather than charging per resolution. If you've got a huge support operation and want autonomous resolution with a model that scales cleanly with your traffic, Ada is a strong pick over Sierra.

4. Cresta

Cresta is a contact-center platform that unifies human and AI agents, combining autonomous agents, real-time agent assist, and conversation intelligence on its own Ocean-1 model. It fits large teams that still run big human contact centers.

Key features

• AI agent: autonomous voice and digital resolution

• Agent assist: real-time coaching and next-best-action for live agents

• Conversation intelligence: full coverage analytics, not sampled

• Quality management: AI scoring against custom rubrics

• Integrations: NICE, Genesys, Five9, Amazon Connect, Salesforce, and more

• Compliance: SOC 2 Type II, HIPAA, ISO 42001, GDPR, and TISAX

Pricing

Custom, contact sales. Cresta uses enterprise module and seat-based pricing that isn't published. Plan for a quote sized to your seats and volume.

Pros

• Lifts both human and AI agents

• Domain model trained on contact-center data

• Deep analytics and QA

• Wide CCaaS integrations

• Strong compliance depth

Cons

• No public pricing

• Heaviest fit for large, human-staffed centers

Best for

Large contact centers that want agent assist, QA, and analytics alongside automation.

Why choose Cresta over Sierra

Sierra focuses on autonomous agents. Cresta keeps your human agents in the loop and makes them better with real-time assist, coaching, and QA. If you still run a large human contact center and want to lift both people and automation, Cresta fits that reality better.

5. PolyAI

PolyAI is a voice-first customer service platform for enterprise. Its agents handle high-volume phone calls end to end, replacing old IVR menus with natural spoken dialog. Voice sits at the core of the product rather than bolted on the side.

Key features

• Voice-native agents: built on a model trained on large volumes of real calls

• Telephony workflows: inbound, outbound, overflow, and routing

• Build tooling: Agent Studio for non-technical teams plus a developer kit

• Analytics: dashboards and plain-language querying

• Integrations: CRM, booking, payments, and contact-center systems

• Compliance: SOC 2, HIPAA, GDPR, and PCI DSS

Pricing

Custom, per-minute, contact sales. PolyAI lists no tiers and quotes per-minute pricing after a demo.

Pros

• Purpose-built for messy phone conversations

• Handles interruptions and accents well

• Enterprise CX integrations out of the box

• Measurement-led deployments

• Strong compliance coverage

Cons

• No public pricing

• Voice-first, so lighter on digital-only use cases

Best for

Enterprises that run high phone volume and want a voice specialist.

Why choose PolyAI over Sierra

If voice is your main channel, PolyAI is tuned for exactly that. Its model handles real phone conditions like interruptions and background noise. Pick PolyAI over Sierra when spoken customer service is the problem you most need to solve.

6. Cognigy

Cognigy, now part of NiCE, is an enterprise agentic AI platform for customer service. It runs autonomous voice and chat agents across the contact center and connects deeply to existing CCaaS systems. The platform is built for large, multilingual operations.

Key features

• Voice and chat: turnkey voice gateway plus 30+ omnichannel connectors

• Agentic AI: goal-driven agents with progressive reasoning

• No-code builder: visual AI Agent Studio for business users

• CCaaS integration: works with NICE, Genesys, Avaya, and more

• Multilingual: 100+ languages and real-time translation

• Compliance: SOC 2 Type II, ISO 27001, HIPAA, and more

Pricing

Custom, contact sales. Cognigy doesn't publish pricing and routes buyers to a demo.

Pros

• Deep contact-center integration

• Very wide language coverage

• Business-user-friendly builder

• Enterprise-grade architecture

• Broad compliance certs

Cons

• No public pricing

• Built for large enterprises, not SMBs

Best for

Large multilingual contact centers adding agents onto an existing stack.

Why choose Cognigy over Sierra

Cognigy is built to layer onto the contact center you already run, with turnkey voice connectivity and 100+ languages. If you operate a large multilingual center and want deep CCaaS ties rather than a new platform, Cognigy is the more natural fit.

7. Parloa

Parloa is an enterprise AI Agent Management Platform that helps contact centers design, test, deploy, and improve autonomous agents across voice and chat. The emphasis is on managing agents over their whole lifecycle, with strong governance built in.

Key features

• Multichannel agents: voice, chat, and messaging as one interaction

• Agent lifecycle: design, test, scale, and optimize in one place

• No-code builder: Parloa Studio for subject-matter experts

• Model orchestration: bring your own LLM, STT, and TTS

• Testing and analytics: simulations, versioning, and monitoring

• Compliance: ISO 27001, SOC 2, PCI DSS, HIPAA, and more

Pricing

Custom, contact sales. Parloa publishes no pricing and sells through a demo and sales process.

Pros

• Full agent lifecycle tooling

• Strong governance and compliance

• Wide language coverage

• Flexible model choice

• Deep CCaaS integrations

Cons

• No public pricing

• Enterprise procurement cycle and budget

Best for

Regulated enterprises that need governed agents across voice and chat.

Why choose Parloa over Sierra

Parloa treats agent management as the core job, with testing, versioning, governance, and monitoring built in. For a regulated enterprise that needs tight control and audit trails across voice and chat, that lifecycle focus can matter more than Sierra's build-once model.

8. Zowie

Zowie is an AI customer service platform known for ecommerce and retail. It started chat-first and now covers chat, email, voice, and social. The standout is tight, deterministic control over sensitive actions like refunds and account changes.

Key features

• Multichannel support: chat, email, voice, social, and API

• Decision Engine: rules-based control for money-touching actions

• Platform modules: build, deploy, and supervise agents

• QA and monitoring: every conversation scored, with reasoning logs

• Multilingual: one build supports 70+ languages

• Compliance: GDPR, SOC 2, EU AI Act, DORA, and HIPAA

Pricing

Custom, contact sales. Zowie uses annual, outcome and usage-based contracts sized to your volume. No prices are published.

Pros

• Deterministic control over risky actions

• Strong ecommerce and retail fit

• Full QA and monitoring

• Wide language coverage

• Flexible model and voice choice

Cons

• No public pricing

• Retail focus may not suit every industry

Best for

Ecommerce and retail brands that want tight control over refunds and account actions.

Why choose Zowie over Sierra

Zowie's Decision Engine keeps sensitive actions on rails, separate from the language model, so refunds and account changes follow your policy every time. For retail teams worried about wrong actions on money-touching workflows, that control is a clear reason to pick Zowie.

9. Five9

Five9 is a cloud contact center platform, or CCaaS. It runs voice and digital channels with routing, workforce management, and a growing set of AI agents and agent-assist tools. The fit here is teams that want a full contact center rather than just an agent layer.

Key features

• Omnichannel CCaaS: voice, chat, email, SMS, and social

• AI agents: autonomous self-service agents across channels

• Agent assist: real-time help, summaries, and live transcription

• No-code automation: IVA and Studio for self-service flows

• Analytics and WFM: reporting, quality management, and workforce tools

• Compliance: SOC 2 Type II, ISO 27001, PCI DSS Level 1, and HIPAA

Pricing

Published. Digital plans start at $119 per seat per month and Core at $159 per seat per month, with a 50-seat minimum. Higher tiers are quote-only.

Pros

• Complete contact center in one platform

• Published entry pricing

• Broad channel coverage

• Strong compliance

• Large integration and partner network

Cons

• Per-seat model, not per-minute

• AI is one part of a bigger, more complex suite

Best for

Mid-market and enterprise teams that want a full AI-driven contact center.

Why choose Five9 over Sierra

Five9 gives you the whole contact center, from routing to workforce management, with AI built across it. It also publishes entry pricing, so you can budget without a quote. If you need a complete platform rather than an agent layer, Five9 covers more ground than Sierra.

10. Voiceflow

Voiceflow is a build-your-own agent platform. Its visual, low-code canvas lets teams design, test, and ship AI agents across voice and chat. The audience is CX and product teams, and agencies, that want to own the build.

Key features

• Visual builder: drag-and-drop design with API and SDK access

• Voice and chat: deploy across multiple channels

• Bring-your-own LLM: use any major model, no lock-in

• Analytics: real-time conversation data

• Team tooling: multi-client workspaces and white-labeling

• Compliance: SOC 2 referenced on site

Pricing

Custom, contact sales. Voiceflow's own pricing page is now quote-only, with an agency path and a business path, both after a demo.

Pros

• Full design control

• Model and channel flexibility

• Good collaboration features

• Strong agency and white-label support

• Large community and templates

Cons

• You build and maintain the agent yourself

• No public self-serve pricing on its own page

Best for

Teams that want to design and own their agent rather than adopt a platform.

Why choose Voiceflow over Sierra

Sierra hands you a managed agent platform. Voiceflow hands you the canvas and lets your team build exactly what you want, with your own models and full control. If in-house ownership and design flexibility matter more than a done-for-you platform, Voiceflow is the better base.

11. Retell AI

Retell AI is a developer-first platform for building AI phone agents. It gives engineers granular control over voices, models, and telephony through an API, with clear per-minute rates published up front. The product aims squarely at technical teams.

Key features

• Voice and chat agents: phone-first, with chat support

• Choice of voices: Retell infra plus ElevenLabs, Cartesia, and more

• Choice of models: GPT, Claude, and Gemini options

• Telephony: Twilio or bring-your-own SIP

• Developer tooling: API, webhooks, transcripts, and add-ons like KB and AI QA

• Compliance: SOC 2 certified, HIPAA-ready with a BAA

Pricing

Published. Pay-as-you-go voice runs from $0.07 to $0.31 per minute, with $10 in free credits. Enterprise is custom.

Pros

• Transparent per-minute pricing

• Granular control over the stack

• Flexible voices and models

• Strong developer experience

• Free credits to start

Cons

• Assembly and coding required

• Less suited to non-technical teams

Best for

Developers who want to build voice agents with fine control and clear costs.

Why choose Retell AI over Sierra

Retell gives you visible per-minute pricing and full control over voices, models, and telephony. If you've got engineers and want to assemble voice agents your way at a price you can see, Retell is a more transparent, hands-on choice than Sierra.

12. Synthflow

Synthflow is a no-code voice AI platform for automating phone calls. It handles inbound and outbound with native telephony, plus agency and white-label tooling. These days it aims mainly at enterprises and resellers.

Key features

• No-code builder: build voice agents without engineering

• Telephony: native network, SIP, or approved enterprise telephony

• Call handling: routing, escalation, and human handoff

• Integrations: CRM, calendar, webhooks, and knowledge sources

• Agency tooling: sub-accounts and white-label rebilling

• Compliance: SOC 2, GDPR, HIPAA, and ISO 27001

Pricing

Published floor. Synthflow's own page is now enterprise-only, starting at $30,000 per year, scoped to your call volume and setup.

Pros

• No-code phone automation

• Native telephony included

• Strong agency and white-label options

• Broad integrations

• Solid compliance

Cons

• Own-page pricing now starts high

• Model and voice provider fees can be separate

Best for

Agencies and enterprises that want no-code phone automation or a reseller model.

Why choose Synthflow over Sierra

Synthflow is a much narrower tool than Sierra, and for some teams that's the point. If all you need is inbound and outbound phone automation you can build yourself or white-label to clients, Synthflow does that job without a full CX platform or an enterprise sales cycle. It suits agencies and teams with a specific calling need, not those standardizing a whole support operation.

Choose the Right Sierra AI Alternative

There's no single best tool here, only the best fit for your needs.

If you run digital support at scale, Decagon and Ada give you strong autonomous resolution, and Zowie adds tight control for retail. If you run a large contact center, Cresta, Cognigy, Parloa, and Five9 cover voice, agent assist, and CCaaS integration. If you'd rather build your own, Voiceflow, Retell, and Synthflow give you the pieces.

If phone and messaging are central, Callers is built for that. It fits your current stack, goes live in weeks, and shows you step-level analytics on every call, all on clear usage-based pricing.

Book a demo to see Callers in action.