Decagon vs Sierra vs Intercom Fin vs Crescendo vs Cresta vs Ada: How to Choose an AI Support Agent
All 6 customer-support agents in our index compared side by side — self-serve software, enterprise sales-led software, a fully-managed service, and a platform built to augment human agents rather than replace them are four genuinely different ways to buy one (Ada and Decagon both sit in the sales-led bucket, a decade apart in maturity), and the right pick depends on which of those you actually want.
By The Agents Index Editorial, Research desk · 2026-07-21
Six names come up whenever a support or CX leader starts shopping for an AI agent to handle customer conversations: Decagon, Sierra, Intercom Fin, Crescendo, Cresta and Ada. All six resolve real support conversations end to end — but read their own researched listings side by side and a much sharper split appears than "which agent is smartest." They are four genuinely different ways to buy the same outcome: software you configure yourself with a sales-led enterprise contract (Decagon, Sierra, Ada), software you can self-serve and trial today (Intercom Fin), an outsourced team-plus-agents engagement you don't configure at all (Crescendo), or a platform built to augment the human reps who stay in the loop rather than replace them outright (Cresta). Which bucket you want usually decides the shortlist before a single feature comparison matters.
The six, at a glance
Every figure below is pulled from each tool's own researched listing, last verified 19–23 July 2026.
| Agent | How you buy it | Pricing | API / self-serve | Best known for |
|---|---|---|---|---|
| Intercom Fin | Self-serve software, layered on any helpdesk | $0.99/resolution (+$29/seat/mo if run on Intercom itself) | Documented API + MCP; 14-day free trial, no card | Most broadly deployed — 12,000+ customers, ~2M resolutions/week |
| Decagon | Enterprise software, sales-led | Custom — no public price list; third-party estimate ~$50K/yr platform fee + $0.99/conversation + $0.50/resolution | No self-serve signup or public API | $4.5B valuation (Jan 2026 Series D); published, named case studies with hard numbers |
| Sierra | Enterprise software, sales-led | Outcome-based, custom-negotiated; escalations to a human are not charged | Agent SDK exists but gated to contracted customers | Bret Taylor/Clay Bavor pedigree; $150M+ ARR by Feb 2026; $15B+ valuation (May 2026); reaches ChatGPT as a channel |
| Crescendo | Fully-managed outsourced CX — not software you run yourself | From $2.99/resolution, all-inclusive (setup, QA, knowledge-base upkeep bundled in) | No API, no self-serve trial — starts with a "proof of value" pilot | $500M valuation plus the PartnerHero acquisition (200+ customers, 3,000+ CX staff folded in) |
| Cresta | Enterprise software, augments human agents rather than replacing them | Custom — one public data point: $150K/yr for Agent Assist alone (chat OR voice), via AWS Marketplace | API-based integrations + MCP; no self-serve signup | Unifies an AI Agent, real-time human Agent Assist and Conversation Intelligence on one record; $280M+ raised, 500+ employees |
| Ada | Enterprise software, sales-led | Custom — no public price list; third-party estimate (Vendr) puts the median contract at $73,500/yr | Documented Conversations/Email API + MCP server; no self-serve signup or free trial | The category's incumbent — founded 2016, $1.2B valuation (2021), one of the few sales-led rivals with a real developer API |
The decision: how do you want to buy this?
All six carry a full researched verdict on their own listing, including who each one is explicitly not for. Read together, the honest decision tree runs on business model first, features second:
- You want to trial an agent today, without a sales call, on top of the helpdesk you already run → Intercom Fin. It's the only one of the six with a public price list, a 14-day no-card free trial, and a documented API/MCP you can start integrating against this week. Watch out for: it bills "assumed" resolutions when a customer simply stops replying, not just genuine fixes, and Intercom's own 76% headline resolution rate is a best case — independent analyses of its published case studies land nearer 40–50% in practice.
- You're a large, well-resourced enterprise that wants a heavily-funded, actively-improving agent you configure yourselves in plain English, and you want published case-study numbers to justify the spend → Decagon. Its Agent Operating Procedures let a support team (not just engineers) write and adjust agent behaviour directly, and its named case studies — Duolingo's 80% deflection, ClassPass's 95% cost reduction — are concrete, not vague marketing. Watch out for: no public pricing at all (only a third-party estimate exists), and reviewers describe real implementations spanning 4–12 weeks of engineering time despite the "plain English" pitch.
- You want the broadest possible reach — including inside ChatGPT itself — and pricing that only ever charges for a genuine resolution → Sierra. Its outcome-based model is one of the cleanest here (escalations to a human cost nothing), and its Agent Studio/Ghostwriter tooling turns existing SOPs into a working agent. Watch out for: it is the most opaque of the six on price — not even a third-party estimate is available — and the Agent SDK is real but gated to signed customers, so there is no way to kick the tires before a contract.
- You don't want to run support software at all — you want an outsourced team that happens to be built on AI agents, especially for a regulated industry → Crescendo. Unlike the other five, you are not buying a platform to configure; you are buying a managed CX operation (agents, QA, staffing, compliance) billed per resolution with a "Total Outcome Guarantee." Watch out for: no API and no self-serve trial by design — every engagement starts with a sales-adjacent "proof of value" pilot — and per-resolution billing needs real volume forecasting to avoid surge fees.
- You want AI automation and real-time support for your human reps unified on one platform — not a tool that only replaces conversations → Cresta. Its AI Agent resolves what it can end to end, then Agent Assist and the newer Knowledge Agent keep guiding the human rep in real time on everything else, all on one shared conversation record, with named results like Xanterra's 74% containment and $3.3M recovered revenue. Watch out for: pricing is among the most opaque here — the only public number anywhere is an AWS Marketplace listing for the narrower Agent Assist product alone ($150,000/year, one channel), and the full AI Agent/Conversation Intelligence suite is custom-quoted with no self-serve tier or free trial.
- You want an established, well-capitalized vendor with a real developer API, and a decade of production history over a newer LLM-native pitch → Ada. Founded in 2016 — years before Decagon, Sierra, Crescendo and Cresta existed — and still backed by $190M+ raised and a $1.2B valuation, its documented Conversations/Email API and MCP server are a genuine developer surface Decagon, Sierra and Crescendo don't publish at all. Watch out for: no public pricing (Vendr's third-party data puts the median contract at $73,500/year) and no free trial, plus a wide admin-vs-end-user satisfaction gap — 4.6/5 on G2 from the teams who configure it, just 2.0/5 on Trustpilot from the customers actually chatting with it.
Decagon vs Sierra: the closest real head-to-head
Of the six, Decagon and Sierra are the closest real rivals — both are enterprise, sales-led, agent-platform software with no self-serve tier, competing for the same large-account budget. The difference is configuration philosophy and pricing transparency, not capability. Decagon's Agent Operating Procedures convert a support team's own plain-English descriptions into agent logic, with Simulations and A/B experiments to test changes before a full rollout; Sierra's Agent Studio plus Ghostwriter does a similar job but leans more visual, and its channel reach goes further — Sierra agents can operate inside ChatGPT itself, which none of the others offer. On price, Decagon is the more knowable of the two: a third-party cost breakdown (roughly $50K/year plus per-conversation and per-resolution fees) at least gives a buyer something to model against, while Sierra's outcome-based rate is negotiated case by case with nothing public to anchor an estimate. Neither is a fit for a team unwilling to run a multi-week sales and implementation cycle — that's the trade both make in exchange for depth.
Cresta: the one built to augment, not replace
Cresta is an outlier by design, not by feature gap. Decagon, Sierra, Intercom Fin, Crescendo and Ada all sell an AI agent that resolves a conversation end to end and treats the human as an exception path; Cresta instead unifies that same kind of autonomous AI Agent with real-time Agent Assist and a proactive Knowledge Agent that keep supporting the human rep through the rest of the conversation, plus Conversation Intelligence analyzing both the AI and human sides on one shared record. That's a genuinely different sale: a contact center trying to replace headcount reaches for Decagon, Sierra, Crescendo or Ada; one trying to make its existing human reps faster and more consistent, while still automating what it can, reaches for Cresta. The catch is pricing transparency — Cresta is among the most opaque here, with the only disclosed number anywhere being a narrow $150,000/year AWS Marketplace listing for Agent Assist alone (one channel, capped volume, non-cancellable), while Decagon and Ada at least have third-party cost estimates and Crescendo publishes its own starting per-resolution rate.
Ada: the pre-LLM incumbent, and the other real developer API
Ada predates every other name on this list by years — founded in 2016, when Decagon, Sierra, Crescendo and Cresta didn't yet exist. That history shows up as a real advantage: $190M+ raised, a $1.2B valuation from a 2021 Series C, and independently-confirmed enterprise customers (TechCrunch named Meta, Verizon and Shopify as live Ada customers in 2023). Alongside Intercom Fin, it's the only other agent here with a genuinely documented developer surface — a Conversations API, an Email Conversations API and an MCP server that most sales-led enterprise rivals in this category simply don't publish. The catch is that publishing docs isn't the same as self-serve access: getting an actual Ada account still runs through the same sales-led process as Decagon, Sierra and Crescendo, so if you want to start building against an API today without a sales call, Intercom Fin remains the only option. Ada's other honest catch is a real gap between how it looks from the admin seat and how it feels from the customer seat: a 4.6/5 rating on G2 (reviewed by the support teams who configure it) sits well above a 2.0/5 on Trustpilot (reflecting the people actually chatting with it), with recurring complaints about lost context and difficulty reaching a human.
One thing four of the six get right (and where Cresta and Ada break the pattern)
Intercom Fin, Decagon and Crescendo all charge per resolution; Sierra charges per successful resolution and explicitly waives the charge on human escalations. None of those four sells a flat per-agent-seat SaaS license the way many support tools historically have — in a category built specifically to replace headcount, "pay for the work done" has become the default pricing logic. Cresta and Ada are the two exceptions, for different reasons: Cresta's one disclosed price (Agent Assist via AWS Marketplace) is a $150,000/year contract for a capped volume of chats or calls, with per-unit overage only once that cap is exceeded — closer to a committed-spend SaaS contract than pure outcome-based billing. Ada's third-party-estimated pricing also scales with monthly conversation volume, but as a platform fee rather than a disclosed per-resolution rate the way Crescendo's or Sierra's structure is at least described — there's simply no public per-unit number to point to either way.
FAQ
Which of these six has a public API?
Only Intercom Fin has one you can access without a sales contract. Ada also publishes a documented Conversations/Email API and an MCP server, but — like Sierra's gated Agent SDK and Cresta's API-based integrations — actually getting access still runs through the same sales-led process as the rest of the enterprise group. Decagon and Crescendo have no self-serve API or signup at all.
Which is cheapest to start using?
Intercom Fin, and it's the only one of the six with a publicly listed starting price ($0.99/resolution) and a free trial. Decagon, Sierra, Crescendo, Cresta and Ada are all sales-led with no public self-serve starting price — Crescendo's $2.99/resolution figure is its own quoted starting rate, Cresta's $150,000/year AWS Marketplace listing is the highest disclosed number, and Ada's third-party-estimated median contract (~$73,500/year, per Vendr) is the closest thing to a public number among the rest — but none of them is reachable without a contract.
What's the real difference between Decagon and Sierra?
Mostly configuration approach and pricing transparency, not capability — see the head-to-head section above. Decagon leans on plain-English Agent Operating Procedures and publishes named case-study results; Sierra leans on a visual Agent Studio, reaches further channels (including ChatGPT), and offers a cleaner "escalations are free" pricing promise, but is more opaque on price.
How is Cresta different from the other five?
The other five sell an AI agent to replace a human conversation, with humans handling only the exceptions. Cresta instead unifies that same autonomous AI Agent with real-time Agent Assist and a Knowledge Agent that keep supporting the human rep for the rest of the conversation, plus Conversation Intelligence analyzing both the AI and human sides on one record — see the section above.
Is Crescendo a software product I install or configure?
No — that's the core distinction from the other five. Crescendo sells a fully-managed CX operation: its own team handles onboarding, ongoing QA and knowledge-base maintenance alongside the AI agents themselves, billed per resolution rather than licensed as a platform.
Do any of these six offer a free tier?
Only Intercom Fin, via its 14-day, no-card free trial. Decagon, Sierra, Crescendo, Cresta and Ada are all enterprise sales-led engagements with no published self-serve or free option.
How does Ada compare to the other sales-led enterprise agents?
Ada, Decagon, Sierra and Crescendo are all enterprise, sales-led engagements with no public pricing — but Ada is by far the most established, founded in 2016 versus 2023+ for the other three, and it's the only one of the four that publishes a documented, self-serve developer surface (a Conversations API, an Email API and an MCP server). The trade-off is a wider admin-vs-end-user satisfaction gap than any of the others show on public review sites — see the Ada section above.
Every agent above carries its own full researched listing — pricing tiers, sourced pros and cons, and a committed verdict on who it's for and who it isn't. Start with the support agents category for the full set, including the other agent-platform vendors that compete on adjacent ground.