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Comparison · Sierra

Assistable vs Sierra

Sierra builds enterprise agents for large brands through an expert deployment team, priced per resolved outcome. Assistable is the self-serve alternative: sign up, get your first assistant and a local number, and make a live call in minutes at $0.07/min all-in.

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<500 ms latency·99.99% uptime·4.7/5 on Trustpilot

The bottom line

Assistable

Assistable runs the whole stack itself and hands you the controls. You sign up, the platform builds your first assistant during onboarding, you buy a local number in-app, and your first live call happens in minutes. Telephony, immutable versioning with one-click rollback, a campaign dial engine, and an LLM judge that grades every conversation are product features you operate directly, at published rates: $0.07/min all-in for voice, $0.02 per message, pay as you go.

Sierra

Sierra is an enterprise Agent OS for large consumer brands, sold through a sales process and deployed with help from Sierra's own expert agent development team, typically in weeks. It overlays your existing contact center, sitting in front of or behind your IVR, and is priced per resolved outcome under a quote-based contract with no published rates.

The real comparison

Six places the platforms actually differ.

The same six questions on every comparison page. Here is how Assistable and Sierra each answer them.

01 / 06

Time to first live call

From signup to an agent answering a real phone call.

Assistable

Sign up at platform.assistable.ai and the platform builds your first assistant during onboarding, grants $10 in usage credit, and sells you a real US or Canadian local number in-app. Your first live call happens in minutes, in one sitting, with no sales call and no engineering. Full production rollouts run 2-3 days because there is no engagement team between you and the product.

Sierra

Sierra is sales-led, with no self-serve signup, no free trial, and no public pricing page. Their product page describes deployment in weeks, supported by an expert agent development team that has backed hundreds of deployments.

Assistable delivers

First assistant created automatically during onboarding·Free local phone number plus $10 in calling credit at signup·US or Canadian local number purchased in-app·Full production rollouts in 2-3 days·Free signup, pay as you go

02 / 06

Infrastructure and telephony

What you assemble before production, and who runs it.

Assistable

Numbers, SIP, recordings, and call control run on the platform's own carrier-grade voice stack, so there is no contact-center platform to integrate and no carrier account to bring. Web chat, SMS, and voice share one channel gateway, and identity resolution maps every phone number, email, and web visitor to one contact record before the agent runs. Compliance rails are built in: DNC scrubbing, honeypot detection, A2P 10DLC registration, and KYC review.

Sierra

Sierra positions voice as a contact-center overlay: agents integrate with any call center platform and can sit in front of or behind traditional IVR systems. That model assumes you already operate the telephony estate, and escalations route back into your existing call center teams.

Assistable delivers

US local and toll-free numbers searched and bought in-app by area code or city·TLS SIP trunk provisioned automatically per imported number·Durable outbox retries 5 times, backing off 30 seconds to 1 hour·0.4s median answer, 99.99% uptime SLA·DNC scrubbing and A2P 10DLC registration built into the platform

03 / 06

Version control and rollback

How changes ship, and how fast you can undo one.

Assistable

Sierra earns real credit here, and Assistable gives you the same rigor as a self-serve product you can inspect. Edits autosave to a working draft while live traffic keeps executing the last published version, and publishing writes an immutable numbered version into an append-only commit log with the author recorded and a Live badge on whichever version the explicit deploy pointer serves. Rollback is one click. Branches stage bigger rewrites and merge into Main without changing the flow id, so phone numbers, endpoints, and channels never re-point.

Sierra

Sierra publishes a genuine release-engineering story: each release is an immutable agent snapshot capturing model versions, knowledge bases, and prompts atomically, with instant rollback and A/B testing across releases. The public material describes snapshots, rollback, and A/B, and does not go deeper than that.

Assistable delivers

Live traffic never executes the open draft after first publish·Append-only version history with author and Live badge in the UI·One-click rollback moves the deploy pointer to any prior version·Branch merges republish without changing the flow id·Publish and rollback are role-gated and audit-logged

04 / 06

Call routing and transfers

What happens when a caller needs a human.

Assistable

Transfers are a configurable engine inside the product, not an escalation into a separate contact-center platform. Warm transfer holds the caller on hold music, hunts your team in order with up to 6 dial attempts and a 25-second default ring timeout per attempt, screens every leg with answering-machine detection so voicemail never gets the call, and speaks a private briefing to the human, static or generated by the LLM from the live transcript, before bridging. Connected, voicemail, no-answer, and failed each route their own flow branch, and unanswered transfers can resume the AI instead of hanging up.

Sierra

Sierra escalates to call center teams using AI-powered intent classification and skills-based routing, and every hand-off includes a detailed AI-generated summary with full context and history. The published model is escalation into your existing contact-center queues.

Assistable delivers

Ordered fallback hunting: up to 6 dial attempts, 25-second default ring timeout·Answering-machine detection screens each transfer leg·LLM-generated whisper briefing from the live call transcript·Tag rules route by contact tag per channel with priority and active hours·A per-minute sweep force-resolves stale holds

05 / 06

Outbound at scale

Dialing a list without burning it.

Assistable

Outbound is a campaign engine, not just an agent that can dial. The engine converges every minute, starting scheduled campaigns and topping running ones to their concurrency cap, with claim-first updates that make double-dials impossible. Calling windows are timezone-aware with day-of-week selection and overnight wrap, retries cover no-answer, busy, and failed while honoring the window, and a wallet at zero pauses the campaign with a stated reason instead of burning the list.

Sierra

Sierra markets outbound voice with precise pickup detection, verified caller IDs, voicemail handling, and warm transfers, and calls it one of its fastest-growing features. The published story is proactive, agent-initiated calling rather than a campaign dialer.

Assistable delivers

A/B traffic splits must sum to 100 before a campaign starts·Per-campaign concurrency and calls-per-minute caps·Enroll up to 25,000 contacts by filter, hand-picked list, or CSV·DND, blacklist, and E.164 checks gate every dial·Outcomes reconcile seconds after hangup via the call webhook

06 / 06

Observability and QA

How you find out something went wrong.

Assistable

Write monitor rules in plain English and an LLM judge grades every finished call and chat against them, not a daily sample. Verdicts cite the decisive moment in the transcript with a confidence score, and repeat failures cluster into issues. The AI then drafts a minimal prompt fix, shows a line diff, and proves it by replaying the failing conversation 3 times through the published flow; confidence is the measured pass rate, never self-reported.

Sierra

Experience Manager is strong and well-documented: real-time monitoring, resolution and CSAT metrics, and tag- and sentiment-based conversation sampling. The QA loop is human-centered, with SMEs formally annotating samples of conversations every day, and annotated conversations can become regression tests replayed against mock APIs.

Assistable delivers

Every finished call and chat graded, not a sample·Verdicts cite the decisive transcript moment with confidence·Fixes replay the failing conversation 3 times; confidence is the measured pass rate·Per-rule health: fire rate, drift, silence, human-overturn rate·Auto-apply is off by default behind hard guardrails

At a glance

Side by side

Getting started

Self-serve signup
AssistableYes
SierraNo
Time to first live call
AssistableMinutes, in one sitting
SierraWeeks, with Sierra's deployment team
Try before you buy
Assistable$10 credit plus free local number at signup
SierraNo

Telephony and routing

Runs its own telephony
AssistableYes
SierraOverlays your contact center
In-app number purchase
AssistableUS local and toll-free, by area code or city
SierraNot published
Warm transfer
AssistableOrdered hunting, AMD screening, whisper briefing
SierraAI-generated summary on hand-off
Call recording and transcription
AssistableYes
SierraYes

Versioning and QA

Immutable versions with instant rollback
AssistableYes
SierraYes
Visible commit log and branches
AssistableAppend-only history, branches merge without changing the flow id
SierraNot published
QA loop
AssistableLLM judge grades every conversation
SierraDaily SME annotation on samples
Regression testing
AssistableReplay failing calls 3x, measured pass rate
SierraConversation tests against mock APIs

Pricing

Model
AssistablePay as you go
SierraOutcome-based, quote only
Voice
Assistable$0.07/min all-in
SierraNo published rates
Messages
Assistable$0.02 per message
SierraNo published rates
Platform, seat, or setup fees
AssistableNone
SierraNot published

Sierra capabilities and pricing reflect their publicly published information as of July 2026 and may change.

Why teams switch

Why teams choose Assistable.

01

Live the day you sign up

Onboarding creates your first assistant, grants $10 in calling credit, and sells you a real local number in-app. The first live call happens in minutes, and full production rollouts run 2-3 day deploys.

02

Version control for agents

Immutable numbered versions in an append-only history, an explicit deploy pointer with one-click rollback, and branches that merge without changing the flow id. Live traffic never executes an open draft.

03

Telephony that behaves like a phone system

Ordered team hunting with answering-machine detection, whisper briefings generated from the live transcript, tag rules with active hours, and DND, blacklist, and wallet gates on every outbound dial.

Under the hood

The infrastructure
most platforms rent.

We operate dedicated network, telephony, and compliance rails, and let you choose the models on top. That is what keeps conversations fast, clear, and safe at scale.

  • Edge

    Co-located edge PoPs and GPUs power low-latency voice AI globally.

  • Telephony

    A full telephony stack built in: native calling and texting without wiring a carrier.

  • Network

    Audio runs on a private global network, bypassing the public internet for call quality.

  • Compliance

    A programmatic compliance layer: DNC and honeypot detection, 10DLC and KYC, attribution reporting.

  • Models

    LLM, TTS, and STT à la carte, self-hosted or from major providers. Enterprises can bring their own keys.

  • Languages

    100+ languages and dialects, with real-time multilingual transcription and translation.

  • Coverage

    Calling and texting in 105+ countries.

Questions

Assistable vs Sierra, answered.

What is the difference between Assistable and Sierra?
Sierra builds enterprise agents for large brands through an expert deployment team, priced per resolved outcome. Assistable is the self-serve alternative: sign up, get your first assistant and a local number, and make a live call in minutes at $0.07/min all-in.
Is Assistable or Sierra more cost effective?
Assistable is usage-based at $0.07 per minute for voice, all-in, and $0.02 per message, with no platform fee, no seat fees, and free pay-as-you-go signup. Sierra's published pricing model is outcome-based, quote only. Assistable bundles telephony, model, and voice into one per-minute rate, so there are no per-component add-ons to reconcile.
When should I choose Sierra over Assistable?
Sierra is a strong choice if you are a large consumer enterprise that wants a partner more than a tool. Outcome-based pricing means Sierra gets paid when a task completes, and escalated cases are in most cases free, which genuinely de-risks a big rollout. Their homepage lists SOC 2, ISO 27001, ISO 42001, HIPAA, GDPR, FedRAMP, and PCI DSS, they support PCI Level 1 card and ACH payments entirely over the phone, and voice runs in 55+ languages with mid-conversation switching. Their published quality lifecycle, with immutable release snapshots, daily SME annotation, and conversation regression tests against mock APIs, is the most mature in the category, and customers like Vanguard, SoFi, and Rocket Mortgage back it up. If you have an enterprise budget, complex integrations, and want an expert team accountable to resolution outcomes, request the demo.
How fast can I get a live AI agent with Assistable?
Signup is self-serve. Onboarding creates your first assistant, grants $10 in usage credit, and lets you buy a US or Canadian local number in-app, so the first live call happens in minutes without a sales call. Full production rollouts run 2-3 days.

Fair is fair

When Sierra is the right call

Sierra is a strong choice if you are a large consumer enterprise that wants a partner more than a tool. Outcome-based pricing means Sierra gets paid when a task completes, and escalated cases are in most cases free, which genuinely de-risks a big rollout. Their homepage lists SOC 2, ISO 27001, ISO 42001, HIPAA, GDPR, FedRAMP, and PCI DSS, they support PCI Level 1 card and ACH payments entirely over the phone, and voice runs in 55+ languages with mid-conversation switching. Their published quality lifecycle, with immutable release snapshots, daily SME annotation, and conversation regression tests against mock APIs, is the most mature in the category, and customers like Vanguard, SoFi, and Rocket Mortgage back it up. If you have an enterprise budget, complex integrations, and want an expert team accountable to resolution outcomes, request the demo.

Results

Take their word for it.

Real operators, verified reviews, and one 18-month evaluation that ended with 25,000 flawless calls.

Platform lifetime

m+managed conversations

Across voice, SMS, WhatsApp, and chat.

Reliability

% uptime

Production uptime, backed by SLA.

Speed

s median answer

From first ring to answered, on every channel.

Verified customer · 18-month evaluation

25,000 calls delivered flawlessly.

“After 18 months testing voice AI platforms including Bland.ai and Synthflow.ai… Assistable delivered flawlessly on over 25,000 calls in recent weeks. It checks all the boxes with built-in features that more mature platforms haven’t integrated yet.”

Maurice M.Verified customer

Backed by a Shark

“Assistable AI is redefining business efficiency.”

KHKevin HarringtonKevin HarringtonOriginal Shark, Shark Tank
Watch →
Trustpilot4.7/5 · 35 verified reviewsHighLevel4.5/5 · 126,000+ marketplace downloads
  • “I've tested a lot of AI and automation tools, and most fall apart once you try to scale. Assistable is the real deal.”
    Jamie WVerified Trustpilot review
  • “I have been using Assistable for about 10 months, and it has changed my business completely. The voice AI quality is unmatched.”
    Travis HolzemVerified Trustpilot review
  • “The conversational quality and flexibility are amazing. Top notch tech and service from the entire team.”
    Eric KnellerVerified Trustpilot review
  • “They make it so easy to get started with voice AI. The onboarding was smooth and the results were immediate.”
    Pam VinjeVerified Trustpilot review
  • “There is no better conversational AI voice bot. There are a ton of players in the market and Assistable leads.”
    Lowe SmithVerified Trustpilot review
  • “Assistable has been a game changer for my business and is way easier to use than any alternative I've tried.”
    Greg PfefferVerified Trustpilot review
  • “Assistable AI was the best decision we have made for our company in a long time. Excellent product and team.”
    Get Amplified MarketingVerified Trustpilot review
  • “Been using Assistable for several months and it has completely changed how our team handles inbound inquiries.”
    ATVerified Trustpilot review
  • “There is no better conversational AI voice bot. There are a ton of players in the market and Assistable leads.”
    Lowe SmithVerified Trustpilot review
  • “Assistable has been a game changer for my business and is way easier to use than any alternative I've tried.”
    Greg PfefferVerified Trustpilot review
  • “Assistable AI was the best decision we have made for our company in a long time. Excellent product and team.”
    Get Amplified MarketingVerified Trustpilot review
  • “Been using Assistable for several months and it has completely changed how our team handles inbound inquiries.”
    ATVerified Trustpilot review
  • “I've tested a lot of AI and automation tools, and most fall apart once you try to scale. Assistable is the real deal.”
    Jamie WVerified Trustpilot review
  • “I have been using Assistable for about 10 months, and it has changed my business completely. The voice AI quality is unmatched.”
    Travis HolzemVerified Trustpilot review
  • “The conversational quality and flexibility are amazing. Top notch tech and service from the entire team.”
    Eric KnellerVerified Trustpilot review
  • “They make it so easy to get started with voice AI. The onboarding was smooth and the results were immediate.”
    Pam VinjeVerified Trustpilot review

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