Comparing Five9 and Sierra AI? Both are Enterprise and Voice & Phone AI tools in the directory, which is why buyers put them on the same shortlist. Below is a side-by-side look at how they price, what they integrate with, and when each is the better fit, so you can pick on the facts rather than either vendor's own sales page.
| Attribute | Five9 | Sierra AI |
|---|---|---|
| Pricing | Paid · $119/seat/mo | Per resolution · Custom |
| Founded | 2001 | 2023 |
| Categories | Contact Center & CCaaS Enterprise Voice & Phone AI | AI Agents & Chatbots Enterprise Voice & Phone AI |
| Integrations | Salesforce ServiceNow Microsoft Dynamics 365 Zendesk Oracle Microsoft Teams Zoom RingCentral | Salesforce Zendesk Shopify Twilio Stripe Snowflake |
Five9 is a cloud contact center platform, the kind that runs the whole operation: inbound and outbound voice, chat, email, SMS, and social messaging, plus routing, quality management, and workforce tools. Its Genius AI suite threads through everything, with voice and digital AI Agents that resolve customer conversations on their own, AI Agent Assist that transcribes calls and coaches live reps, and AI Summaries, Insights, and Knowledge doing the after-call cleanup. In 2025 Five9 pushed hard into what it calls Agentic CX, adding an Agentic Engine plus AI Trust and Governance controls.
The company has been at this since 2001, when it started in San Ramon, California, betting that contact centers belonged in the cloud back when they lived in server closets. It went public on NASDAQ in April 2014 at 7 dollars a share under the ticker FIVN. In 2021 Zoom agreed to buy Five9 for roughly 14.7 billion dollars in stock, then shareholders balked and the deal was terminated that September. Longtime CEO Mike Burkland retired, handing the job to Amit Mathradas in February 2026. Today Five9 claims more than 3,000 customers, including Alaska Airlines, PUMA, Omaha Steaks, Wyndham, and Exact Sciences.
Five9 publishes exactly two prices. Digital costs 119 dollars per concurrent seat per month for digital channels only, and Core costs 159 dollars with voice included. The Plus, Pro, and Enterprise bundles are quote only, and everything carries a 50 seat minimum plus usage based charges. Bundled AI covers 3,000 minutes per seat before metered fees kick in, and the serious stuff, AI Agents and virtual agents, is sold as add-ons through sales. Budget accordingly.
Choose Five9 if you run a genuine contact center with 50 or more seats and want voice, digital channels, and AI under one roof from a vendor that will still exist next year. Skip it if you are a small team wanting a simple helpdesk: Zendesk or Intercom will fit better, cost less, and skip the sales calls.
Read the full Five9 listing → · See Five9 alternatives →
Sierra builds conversational AI agents for the enterprise, and it arrived with about as much star power as a startup can carry. It was founded in 2023 by Bret Taylor and Clay Bavor, and if those names ring a bell it is because Taylor co-created Google Maps, served as CTO of Facebook and co-CEO of Salesforce, and currently chairs the board of OpenAI, while Bavor spent eighteen years at Google leading its virtual and augmented reality work. Company lore says the whole thing was hatched over a grilled branzino lunch in Palo Alto.
The product lives up to the pedigree. From a single build, Sierra deploys a branded agent across chat, voice, email, SMS, and even ChatGPT, following your policies, adopting your brand's voice, and escalating gracefully when a conversation gets thorny. Its voice agents are a standout: they hold natural, low-latency conversations, read sentiment, and can even take a credit card or ACH payment over the phone in one uninterrupted call, with no clumsy handoff to a separate system.
Under the hood sits Agent OS, a platform for building, testing, and supervising agents, with tooling to run voice simulations and rehearse behavior before anything reaches a real customer. Pricing is outcome-based, tied to conversations or successful resolutions and wrapped in multi-year enterprise contracts, so Sierra is aimed at large brands rather than weekend experimenters. Reported customers include SoFi, Ramp, and Brex, and the company says its agents already serve a meaningful slice of the Fortune 50.
Sierra's fundraising has kept pace with its towering ambition, vaulting the company into the rarefied tier of the most valuable AI startups in barely two years. For enterprises that want polished, on-brand agents across every channel and are willing to invest the time and budget to do it properly, Sierra is a genuine marquee choice.
Read the full Sierra AI listing → · See Sierra AI alternatives →
Submit your AI customer support software to get listed alongside these tools and show up in head-to-head comparisons.