Retell AI vs Sierra
Which Agents AI tool is better in 2026?
Retell AI
Hire your AI call center for sales, support, and appointment scheduling
Sierra
Conversational AI agents for every business
Side-by-side
Sierra is the more established option (raised $2.2B); pricing is comparable on both sides.
| Metric | Retell AI | Sierra |
|---|---|---|
| Taglinei | Hire your AI call center for sales, support, and appointment scheduling | Conversational AI agents for every business |
| Foundedi | 2023 | 2023 |
| HQi | US | San Francisco, US |
| Employeesi | 1-10 | 100-200🏆 |
| Neuron scorei | 60 | 89🏆 |
| Total fundingi | Undisclosed | $2.2B🏆 |
| Latest roundi | Seed | Series D · May 2026 |
| Valuationi | — | $15.8B🏆 |
| Cheapest paid plani | — | — |
| Free plani | ✓ Free Trial | ✗ |
| Free triali | ✓ | ✗ |
| Top tier pricei | Enterprise · Contact sales | Enterprise · Contact sales |
| Pricing summaryi | 2 published plans | 1 published plans |
| Categoriesi |
Capability matrix
Developer-facing capabilities and access signals for Retell AI and Sierra.
| Capability | Retell AI | Sierra |
|---|---|---|
| MCP support | ✗ | ✗ |
| Public API | ✗ | ✗ |
| Webhooks | ✗ | ✗ |
| OAuth 2.0 | ✗ | ✗ |
| SDK languages | 2 (JavaScript, Python) | — |
| Free plan | ✓ | ✗ |
| Free trial | ✓ | ✗ |
| Verified | ✗ | ✓ |
| Active deal | ✗ | ✗ |
🟢 Strengths of Retell AI
- Offers a free plan
- Offers a free trial
🔵 Strengths of Sierra
- Has raised more capital ($2.2B vs Undisclosed)
- Higher Neuron score (89 vs 60)
- Verified profile
Which should you choose?
Choose Sierra if price matters most — it starts at Enterprise · Contact sales, which is friendlier for teams watching burn. Both AI Agents tools ship core features, so the cost delta often decides it for small teams and solo operators.
Choose Sierra if you want the most established option — it has raised $2.2B, suggesting more runway for enterprise features, support, and long-term roadmap. For mission-critical workflows or larger teams, that stability often outweighs a lower monthly price.
Frequently asked questions
Retell AI vs Sierra — which is better?
It depends on your priority. Retell AI is the leaner option; Sierra has broader feature depth. See the side-by-side table above.
Is Retell AI cheaper than Sierra?
No — Sierra's cheapest paid plan is Enterprise · Contact sales, while Retell AI's is Free.
Do Retell AI and Sierra offer free plans?
Retell AI: Yes, has a free plan. Sierra: Paid only.
Explore more AI Agents tools
Contextual paths to related AI startups, deals and rankings.