9 best Sierra alternatives in 2026, compared
Samuel Oram-Jones, 11 min read
The best Sierra alternatives in 2026 are Bland, Synthflow, Replicant, Cognigy, Kore.ai, PolyAI, Voiceflow, Ada, and Retell, and Bland ranks first for enterprise phone calls because it is full stack. This ranking compares each voice AI provider on how it charges, who builds the AI, and where calls can run, as of November 2026.
What are the best Sierra alternatives?
The best Sierra alternative overall is Bland, because one company builds every model on a call and prints what a minute costs.
- Bland: Best overall for enterprise phone calls
- Synthflow: Best for teams that sign one annual voice contract
- Replicant: Best for contact centers that want a quoted, vendor-run agent
- Cognigy: Best for enterprises with a platform team that connects its own models
- Kore.ai: Best for enterprises that run chat and voice agents on one platform
- PolyAI: Best for teams that want a managed service
- Voiceflow: Best for customer experience teams that design agents in a visual studio
- Ada: Best for support teams that automate chat, email, and voice
- Retell: Best for engineers who pick their own model and voice
Why do teams look for Sierra alternatives?
Teams look for Sierra alternatives when a bill cannot be forecast and a security review keeps growing, because Sierra publishes no rate and routes each turn across frontier, open-weight, and some of its own models.
Sierra says "With outcome-based pricing, Sierra gets paid only when we complete a task for you," and Sierra adds that routing or greeter-style interactions may be priced on conversation count "regardless of the outcome," so a finance team gets a figure only from an order form.
Sierra also says "Sierra automatically switches between LLM providers to optimize your agent," which means the model behind a caller's reply can change without the customer choosing it. Each provider behind that switch is one more company in a security review. Sierra sells one agent across chat, SMS, WhatsApp, email, and voice, and a team that mostly takes phone calls may want a provider where phone is the main product.
Sierra supports Apple Business Chat among its messaging channels, which matters to teams that want branded iMessage threads on the same flows as voice. Buyers comparing options should also ask who signs a BAA, the contract HIPAA requires before a vendor handles patient information, and where calls can run. For a direct comparison of two providers, Bland vs Sierra goes line by line.
As of November 2026, Sierra started as a chat-first platform for customer support and added voice later, and it has no self-serve mode, so a team can't build and test an agent before an order form.
Sierra's FedRAMP High is held through Knox Systems, under whose platform it is listed, rather than its own authorization, while Bland holds FedRAMP 20x Class A.
How do the 9 best Sierra alternatives compare?
These nine voice AI providers differ most in how they charge and in how much of a call each one builds, and Bland is the one that publishes a per-minute rate for all of its AI.
1. Bland: Best overall for enterprise phone calls
What does it do? Bland is a full stack voice AI provider that builds and runs its language, speech, and transcription models for inbound and outbound calls. It publishes sub-200ms latency and support for 1 million concurrent calls, and teams build calls in Pathways as connected steps they can test before launch.
Who is it for? Enterprises and contact centers running high-stakes calls at volume, including teams that want iMessage beside voice.
Pros
- No outside AI lab in the call path, so a security team reviews one AI company
- Dedicated orchestration and dedicated GPUs run by Bland, on Enterprise
- BAA on Enterprise, PCI DSS self-attested, FedRAMP 20x Class A
- Bland Speech v3 ranked first of 13 AI voices on Audio Realism Bench on 4 August 2026
- Forward-deployed engineers on Enterprise
- Native iMessage agents on Enterprise, sharing pathways with voice
- Staged releases that pause a new agent version when it performs worse than the last
- Call grading on the audio as well as the transcript
Cons
- Overkill for a small prototype, because Bland is built for production calls at volume
Idaho Housing and Finance Association saves $750,000 a year by replacing its IVR with Bland, which handles 4,000 inbound calls a day and cut average call time by 20%.
"We save thousands of dollars a day."
Greg Blake, Chief Information Officer, Idaho Housing and Finance Association
Pricing: Self-serve Start is $0.14 per minute with no platform fee, self-serve Build is $0.12 per minute with a $299 monthly platform fee, and Enterprise is priced to volume. Phone is billed separately at carrier cost. Enterprise adds native iMessage agents, warm transfers, a BAA, SSO, data residency, dedicated GPUs run by Bland, and forward-deployed engineers, alongside SMS and web chat.
2. Synthflow: Best for teams that sign one annual voice contract
What does it do? Synthflow sells voice agents through one annual enterprise agreement that scopes in telephony, integrations, and launch support, and Synthflow offers WhatsApp and SMS chat beside voice.
Who is it for? Mid-market and enterprise teams that want a sales-scoped platform and will sign before they launch.
Pros
- SOC 2 Type 2, ISO/IEC 27001, HIPAA, and GDPR coverage
- Forward-deployed engineers launch agents with a customer's team where the agreement includes launch support
- Its own text-to-speech engine
Cons
- "Synthflow has no free plan or trial and no rate by the minute"
- Advertises <500ms latency and "99.99% uptime", while its terms test "P90 ≤ 2,800 ms bot response time"
- Says it is "Powered by proprietary orchestration and models from OpenAI, ElevenLabs, Deepgram, and custom in-house logic."
- No iMessage agents
Pricing: Annual agreement only, with purchased numbers at $1.50 a month.
3. Replicant: Best for contact centers that want a quoted agent
What does it do? Replicant sells AI agents for customer service across voice, chat, and SMS, and prices by quote.
Who is it for? Large contact centers that want a vendor-run deployment with contracted business outcomes.
Pros
- Voice, chat, and SMS on one platform
- SOC 2 Type 2, PCI DSS, and HIPAA certifications
- Says its platform is aligned with GDPR
Cons
- No public rate, only a pricing request
- Model providers undisclosed
- No iMessage agents
Pricing: Quote through a pricing request.
4. Cognigy: Best for enterprises with a platform team
What does it do? Cognigy sells a conversational AI platform that connects to language, speech, and transcription providers the customer chooses, including OpenAI, Azure, Anthropic, Amazon Bedrock, Google, and Mistral AI.
Who is it for? Large contact centers with their own platform team that want to wire together their own model and speech vendors.
Pros
- Voice Gateway connects an agent to the phone network over SIP
- SOC 2 Type II, ISO 27001, GDPR, and a HIPAA Type 2 report
- A wide choice of model and speech providers
Cons
- Cognigy says "Ensure that you have all the necessary API credentials to access the specific LLM you intend to use."
- Every connected provider is another company in a security review
- Pricing is a demo request, with no published rate
- No iMessage agents
Pricing: Quote through a demo request. Read Best Kore.ai alternatives for a platform with a similar enterprise shape.
5. Kore.ai: Best for enterprises that run chat and voice agents on one platform
What does it do? Kore.ai sells an enterprise agent platform for service, work, and process automation across digital and voice channels, with a native Voice Gateway.
Who is it for? Large enterprises that want one platform for chat, messaging, and voice agents.
Pros
- Messaging, social, email, SMS, and voice channels
- Speech-to-text and text-to-speech providers are set per language
- New workspaces get free credits worth $500
Cons
- Billed per session, not per minute, so a rate cannot be set beside a per-minute price
- Support plans start at $1,000/month
- No iMessage agents
Pricing: $0.20 per session, usage-based. On Enterprise a session is "the billing unit clocked for 15 minutes of interaction with the bot," and the plan is customized by contacting Kore.ai.
6. PolyAI: Best for teams that want a managed service
What does it do? PolyAI builds and runs a voice and chat agent for a customer, and ongoing use is priced per minute by quote. It also sells a Dialog-RSN-1 model API at 2¢ a minute.
Who is it for? Large consumer-facing companies that want PolyAI to build and run their agent.
Pros
- PolyAI handles the build
- Its own Raven model alongside OpenAI and Claude models
- SOC 2 Type II and ISO 27001
Cons
- No public per-minute rate on its managed agent
- Its contract says "the total handle time is rounded up to the next 30-second increment"
- Its model API leaves telephony and orchestration out
- No iMessage agents
Pricing: Quote only for the managed agent. Teams weighing a similar move from another vendor can read Best Parloa alternatives.
7. Voiceflow: Best for customer experience teams that design agents in a visual studio
What does it do? Voiceflow is a platform for building, testing, and deploying chat and phone agents, with a choice of the large model providers or a customer's own model.
Who is it for? Customer experience teams and agencies that design agents visually and pick their own models.
Pros
- Visual studio across voice and chat
- Free trial with no credit card
- Says it does not use customer data to train any model
Cons
- Every interaction consumes credits that vary by vendor and model, so a minute has no single price
- Enterprise pricing is by request
- Phone is a Twilio-style connection to a number the customer brings
- No iMessage agents
Pricing: Usage-based billing in credits, with pricing on request.
8. Ada: Best for support teams that automate chat, email, and voice
What does it do? Ada sells an agentic customer experience platform that deploys customer service agents across voice, messaging, and email.
Who is it for? Enterprise support teams that handle high volumes of customer inquiries on several channels.
Pros
- Voice, messaging, and email in one Conversation Hub
- HIPAA, SOC 2, GDPR, and PCI DSS
Cons
- Charges for every conversation, so a long call and a short one can cost the same
- Resolution-based pricing is offered to enterprises with specific needs
- No iMessage agents
Pricing: Per conversation, or per resolution for some enterprises, with no published rate. Teams comparing chat-led support agents can read Decagon alternative for enterprises.
9. Retell: Best for engineers who pick their own model and voice
What does it do? Retell is a platform for building and monitoring voice and chat agents, billed per minute with the language model and voice priced as separate lines.
Who is it for? Developer-led teams that want to choose their own language model and voice.
Pros
- A wide choice of language models and voices
- SOC 2, HIPAA, and GDPR coverage
Cons
- Advertises "We guarantee >99.9% uptime", while its terms say "at least 99.5% uptime"
- Language model and voice bill as separate lines on top of voice infrastructure
- No iMessage agents
Pricing: $0.07 to $0.31 per minute depending on the language model and voice, with Retell Voice Infra, GPT-4.1, and an ElevenLabs Flash voice coming to $0.14 per minute before phone.
How does one call run on Bland and on Sierra?
A call on Bland stays with one AI company, while a call on Sierra can touch several AI companies, counting Sierra.
1 AI company on each call
$0.14 a minute for all of its AI on self-serve Start, no platform fee
- TranscriptionSeveral providers, not named
- Language modelA constellation of LLMs that combines frontier, open-weight, and proprietary models
- SpeechA constellation of voice models, none named
Several AI companies on each call, counting Sierra
No published rate a buyer gets a quote from sales
Which of these sounds most human?
Bland ranks highest of these providers on Design Arena's Audio Realism Bench: Bland Speech v3 ranked 1st of 13 AI voices at 1365 on 4 August 2026. Sierra says "Every turn is routed to the optimal model."
- #1BlandBland Speech v31365
- 2ndMicrosoftMAI-Voice-21224
- 3rdxAIGrok TTS1156
- 4thOpenAIGPT Realtime 21119
- 5thGoogleGemini 2.5 Pro TTS1109
- Not rankedSierra's own voicesNot ranked
Ranks are among 13 AI voices, and Sierra's own voices weren't ranked. Real human recordings scored 1500, at the right edge of this scale. Bars start at 600, not zero. Source: Design Arena's published results.
How much do Sierra alternatives cost?
Sierra alternatives split into providers that publish a rate, such as Bland's self-serve Start plan at $0.14 per minute and Retell at $0.14 per minute before phone, and providers that quote, which is Sierra's own model. Synthflow, Replicant, Cognigy, and PolyAI sell by quote or annual agreement, Kore.ai charges per session, and Ada charges per conversation. Enterprise pricing is custom, set with Bland's sales team.
A rate that leaves out the language model can't be compared with one that includes it, so these two bills price the AI in one production minute, before phone.
What does each Bland plan include?
| Included | Self-serve: Start | Self-serve: Build | Enterprise (custom) |
|---|---|---|---|
| Price per minute | $0.14 | $0.12 | Custom |
| Platform fee | $0 | $299 a month | Contracted to volume |
| Transfer time per minute | $0.05 | $0.04 | Custom |
| Concurrent calls | 10 | 50 | Custom |
| Calls a day | 100 | 2,000 | Unlimited |
| Knowledge bases | 10 | 50 | Unlimited |
| Voices | 1 | 5 | Unlimited |
| Uptime SLA | 99.9% | 99.9% | 99.9% |
| Pathways, integrations, and automations | Yes | Yes | Yes |
| iMessage, SMS, and web chat | No | No | Yes |
| Warm transfers and guardrails | No | No | Yes |
| BAA, SSO, and data residency | No | No | Yes |
| Dedicated orchestration and GPUs | No | No | Yes |
| Forward-deployed engineers | No | No | Yes |
| Vendor | What a minute pays for | Total per minute | Phone |
|---|---|---|---|
| Bland Start (self-serve) | All AI: model, transcription, speech $0.14 | $0.14 before phone | Billed separately at carrier cost |
| Retell | Voice infrastructure $0.055, GPT-4.1 $0.045, ElevenLabs Flash voice $0.04 | $0.14 before phone | Twilio at $0.015 a minute, billed on top |
Bland Start (self-serve): Self-serve Start has no platform fee. Self-serve Build is $0.12 a minute plus $299 a month. Phone and transfers bill separately. Retell: Retell Voice Infra, GPT-4.1, and an ElevenLabs Flash voice, before Twilio phone minutes.
What does moving off Sierra involve?
Moving off Sierra means rebuilding conversation flows on a new platform and keeping numbers by connecting a carrier over SIP, starting with one flow a team handles every day.
The safest path runs the rebuilt flow beside Sierra on a share of live calls, with the outcome definitions from the Sierra order form turned into a per-minute budget before launch. Transcripts and recordings should be exported before a workspace is closed. On Enterprise, Bland's forward-deployed engineers work beside a customer's team on its first agent.
Bland's staged releases suit that run, because a new agent version takes a small share of calls, Bland benchmarks it against the previous version, and the rollout pauses when a KPI such as escalation rate gets worse.
How were these alternatives ranked?
Each provider was compared on how it charges, who builds the AI, deployment, compliance, and voice realism, with weight on what enterprise phone calls need. Voice scores come from Design Arena's chart of 4 August 2026.
For more, Bland vs Sierra, this Sierra AI review, and Sierra alternative for enterprises go further, Compare enterprise voice AI agents covers every provider, and a demo built on a real customer workflow is the quickest next step.
Frequently asked questions
What is the best alternative to Sierra?
Bland is the best alternative to Sierra for enterprise phone calls, because one company builds every model on a call and Bland publishes self-serve $0.14 and $0.12 per minute rates before any sales conversation.
Is there a Sierra alternative with published pricing?
Yes. Bland publishes $0.14 per minute on self-serve Start and $0.12 on self-serve Build with a $299 monthly fee, covering all AI before phone, and Retell publishes $0.07 to $0.31 per minute with the model and voice as separate lines. Sierra publishes no rate.
Which Sierra alternative is best for healthcare?
Bland is the best Sierra alternative for healthcare, because it includes a BAA on Enterprise and builds its own language, speech, and transcription models, so no outside AI lab sits in the call path.
Which of these platforms has no outside AI vendors?
On Bland, the language model, speech, and transcription are all built by Bland. The other eight use outside providers or leave them undisclosed, and Sierra says it combines "frontier, open-weight, and proprietary models."
Which Sierra alternatives support iMessage?
Bland is the one provider here that runs branded iMessage agents natively, on its Enterprise plan. Sierra supports Apple Business Chat, and Synthflow, Replicant, Cognigy, Kore.ai, PolyAI, Voiceflow, Ada, and Retell don't offer iMessage agents as of November 2026.
Is Bland only for outbound calls?
No. Bland runs inbound and outbound calls, plus SMS, web chat, and iMessage on Enterprise, on the same Pathways.
How do I move my calls from Sierra?
Rebuild one conversation flow on a new platform first and keep existing numbers by connecting a carrier over SIP.
