Sierra

Our full take

Sierra is the blue-chip enterprise option in this directory, and it does not look like anything else on the list. It is the company Bret Taylor and Clay Bavor started in early 2024. Taylor is the former co-CEO of Salesforce and the chair of OpenAI’s board, Bavor is a long-time Google executive, and that pedigree shows up in who Sierra sells to and how. By May 2026 the company had raised a $950 million round at a reported $15.8 billion valuation, with around $150 million in annual recurring revenue and close to 40% of the Fortune 50 named as customers (press reporting, May 2026).

What Sierra actually sells is a managed AI agent for customer experience. You do not log in and drag boxes around to build a phone bot. Sierra builds and runs a branded agent for your company across chat, voice, email, SMS, WhatsApp and even ChatGPT, and the voice side is a real product, not an afterthought. The named customers are the proof point: SiriusXM, Sonos, ADT, WeightWatchers, Ramp, Chime, Sutter Health and Rocket Mortgage all appear on Sierra’s own customers page. WeightWatchers in particular has been cited publicly handling a large share of its customer sessions through the Sierra agent. These are big brands putting real call volume on the platform, which is a different signal from a long logo wall of pilots.

Now the part that makes Sierra genuinely different: the pricing. Most vendors here bill you per minute. Sierra bills you per resolution. That means you pay when the agent actually resolves a customer’s issue, not for the time spent on the call or for a per-seat licence. Sierra’s own site frames it as paying for the value delivered, and Taylor has talked publicly about outcome-based pricing being the model the company is built on. The appeal is obvious. Your cost lines up with results, so you are not paying for calls that go nowhere. The honest catch is just as important, and I will not paper over it: the actual per-resolution rate is not public. Pricing is enterprise, sales-led and quoted per contract. Public reporting has put typical deals in the low-to-mid six figures a year, but that is third-party reporting, not a Sierra rate card, so treat it as directional rather than a quote you can hold them to. Because there is no per-minute number to give you, every per-minute field on this page reads 0. That is a convention here, not a measured cost. The real answer is “you have to talk to sales”.

So who is this actually for? Large brands with real support volume, a procurement process, and a customer-experience problem big enough to justify a managed partner. If that is you, the outcome-based model is attractive precisely because it ties spend to resolved issues. If you are a founder, an agency or a solo builder who wants a working phone agent live this week for a few cents a minute, Sierra is the wrong shelf entirely. Look at the turnkey platforms in this directory instead. There is no self-serve signup, no published price, and no affiliate or referral programme we could find, so we have flagged the affiliate reliability as “unverified” simply because there is nothing to verify.

On compliance, Sierra reads strong for a regulated buyer, and this matters more here than for a hobby project because the customers are banks, insurers and health systems. Sierra’s own trust page lists SOC 2, HIPAA, GDPR, PCI, CCPA, CSA STAR, ISO 27001 and ISO 42001, and states that personal information shared with the agent is automatically encrypted and masked. ISO 42001 is the AI-specific management standard and is still rare to see, so Sierra carrying it is a genuine signal. We have marked HIPAA, SOC 2 Type 2 and GDPR true on the strength of Sierra’s own published statements. One caveat we will keep honest: Sierra’s site lists “HIPAA” and describes HIPAA safeguards rather than spelling out a self-serve BAA, and the SOC 2 Type 2 distinction comes from secondary reporting rather than a report we have read ourselves. If you are buying for a regulated workload, ask Sierra directly for the current SOC 2 report and a signed business associate agreement before you commit.

My read: Sierra is the most enterprise thing in this directory, and the outcome-based pricing is a real point of difference rather than marketing gloss. The trade-off is access. You cannot try it cheaply, you cannot see the price, and you are buying a managed service, not a builder. That is a fair deal for a large brand and a non-starter for everyone else.

We have not placed our own test calls to Sierra yet, so there are no Voxrater latency numbers on this page. Sierra is enterprise and sales-gated, so a like-for-like test call is harder to arrange than for the self-serve platforms, and we will say so plainly rather than publish a number we have not measured. The positioning, customers and compliance detail above are from Sierra’s own site, captured 2026-05-31. The funding and revenue figures are from press reporting on the same dates.

AI-assisted research, sourced and reviewed by Voxrater, last reviewed 2026-05-31. Every claim above links to a dated source. We have not yet call-tested Sierra, so no benchmark latency is shown. Voxrater may earn affiliate commission from some vendors; Sierra is not one of them (no affiliate programme found). Independent benchmark, no vendor spin.