What it is
Sierra builds AI agents that talk to customers for large companies, covering support and also sales, retention and longer jobs such as mortgage applications and insurance claims. One agent can be deployed across chat, SMS, WhatsApp, email, voice and inside ChatGPT. Teams build agents without code in Agent Studio or in code with the Agent SDK, and Ghostwriter, which Sierra calls the agent-building agent, can turn SOPs, call transcripts, whiteboard photos or a plain description into a working agent, then update it from flagged conversations.
Other parts of the platform include Horizon for long-running tasks and customer memory, a Context Engine, and Insights (Explorer, Monitors, Experiments and Observability) for checking what agents do. Sierra lists SOC 2, ISO 27001 and 42001, HIPAA, GDPR, PCI DSS and FedRAMP High, and in October 2026 announced AIUC-1, an audited standard aimed specifically at AI agent behaviour.
Pricing is outcome-based: customers mainly pay when the agent resolves an issue, but no rates are published. In May 2026 Sierra raised $950 million at a reported $15.8 billion valuation. Named customers include Rocket Mortgage, SiriusXM, Gap, Uber, Vanguard, Santander, Wayfair, Discord and Docusign.
Our review
Sierra's strongest argument is not its software but its paperwork. FedRAMP High, PCI DSS, HIPAA and ISO 42001 are hard to assemble, and in October 2026 it added AIUC-1, an audit by Schellman that tests how agents behave when someone tries to manipulate them. For a bank or insurer, that list shortens a security review that would otherwise take months.
The engineering details back it up. Sierra's documents say payment card data runs through separate PCI infrastructure and never reaches the core platform or the language models, personal data is masked automatically, and customers are logically isolated by tenant. Deterministic guards enforce rules such as authentication that the model is not trusted to judge. The Agent SDK page states that customer data is never used to train models; the trust page phrases it more loosely, as data used only as the customer instructs, so procurement should put the stronger wording in the contract.
Outcome pricing is the commercial hook and the hardest clause to write. Sierra says unresolved conversations are usually free, but some routing and greeting interactions are billed per conversation regardless. Decagon, its closest rival, publicly argues that most buyers prefer per-conversation pricing to avoid haggling over what counts as resolved. Sierra publishes no rates, and per-resolution figures in circulation come from third parties rather than the company.
Scale is no longer in question. A $950 million round in May 2026 at a reported $15.8 billion valuation means the vendor will be around, and Ghostwriter addresses the slowest part of deployment by drafting agent logic from existing SOPs and transcripts. What a mid-size company cannot do is try any of this: there is no trial, no sandbox and no published price, while Intercom Fin lists a price per resolution that anyone can read.
Where it earns its place
The head of customer operations at a mortgage lender
Automate status checks and document chases across phone and SMS
One agent covers voice and messaging, and Horizon tracks a case that runs for weeks. Billing is per outcome, so the contract has to define when a document chase counts as resolved; rates are negotiated, not published.
A security architect at a US federal contractor or bank
Approve an AI agent that will handle payments and personal data
Sierra lists FedRAMP High and PCI DSS, keeps card data on separate infrastructure, and offers SOC 2 and penetration test reports through trust.sierra.ai. Ask for the no-training clause in the DPA, since public pages word it differently.
A platform engineer on a 10-person CX engineering team
Build agent logic in code with tests and version control
The Agent SDK sits alongside the no-code Agent Studio, and Observability shows tool calls, knowledge lookups and latency per conversation. Access comes only after a sales contract.
Before you commit
- Setup
- Sales-led: no trial or self-serve sign-up; Ghostwriter can draft a first agent from SOPs and transcripts once a contract is in place.
- Integrations
- Chat, SMS, WhatsApp, email, voice and ChatGPT as channels; Agent SDK for code-defined agents; back-end systems connected per deployment.
- Data and privacy
- Tenant isolation, encryption at rest and in transit, automatic PII masking, PCI-isolated payment handling; SOC 2, ISO 27001 and 42001, HIPAA, FedRAMP High; subprocessors listed at trust.sierra.ai.
- Cost at scale
- Not published; Sierra bills mainly per resolved outcome, with some interactions per conversation, under annual enterprise contracts.
- Limits
- No public rate limits, SLAs or language list; outcome definitions are negotiated per contract.
What's good
- FedRAMP High, PCI DSS, HIPAA, ISO 42001 and AIUC-1
- Card data kept off the core platform and the models
- Ghostwriter drafts agents from SOPs and call transcripts
- One agent across chat, voice, messaging and ChatGPT
What's not
- No public pricing, trial or sandbox
- Some interactions billed per conversation, not per outcome
- Training policy worded differently across Sierra's own pages
- Built and sold for large enterprises only
Best for
Large and regulated enterprises deploying AI agents across chat and voice.
Alternatives
Sierra: common questions
- Is Sierra worth it?
- Sierra is what a regulated enterprise buys when it wants an AI agent with an audit trail and a vendor that bills only when the work gets done. We rate it 4.5 out of 5.
- How much does Sierra cost?
- Outcome-based enterprise contracts (you pay mainly for resolved conversations); no public rates, trial or self-serve plan.
- What are the downsides of Sierra?
- No public pricing, trial or sandbox; some interactions billed per conversation, not per outcome; training policy worded differently across Sierra's own pages; built and sold for large enterprises only.
- Who is Sierra best for?
- Large and regulated enterprises deploying AI agents across chat and voice.
- How much does Sierra cost for a team or in production?
- Not published; Sierra bills mainly per resolved outcome, with some interactions per conversation, under annual enterprise contracts.
- Is Sierra safe for company data?
- Tenant isolation, encryption at rest and in transit, automatic PII masking, PCI-isolated payment handling; SOC 2, ISO 27001 and 42001, HIPAA, FedRAMP High; subprocessors listed at trust.sierra.ai.
- What are the best Sierra alternatives?
- The closest alternatives we have reviewed are Decagon, Intercom Fin and Ada.
Answers checked Oct 22, 2026.
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