Compare / Retell AI vs Vertex AI Agent Builder
Head-to-head
Retell AI vs Vertex AI Agent Builder.
Side-by-side on ratings, pricing, pros, cons, and the honest take on which to pick. Cross-category comparison: Retell AI is a voice ai agent and Vertex AI Agent Builder is a enterprise platform.
| Retell AI | Vertex AI Agent Builder | |
|---|---|---|
| Rating | 4.0 / 5 | 3.5 / 5 |
| Category | Voice AI Agent | Enterprise platform |
| Tech level | low code | developer |
| Open source | No | No |
| Pricing | Pay-per-minute usage: ~$0.07–0.10 per minute of voice conversation. Free tier with limited minutes. Volume discounts at enterprise scale. | Usage-based on Google Cloud: per-token Gemini model costs + Vertex AI infrastructure. Free tier credits available for new accounts. |
| Best for | B2B teams deploying voice agents for outbound sales, customer support, or appointment booking. Strong for builders who want a managed voice infrastructure without owning the telephony stack. | Engineering teams on Google Cloud who want to build agents using Gemini's long-context capabilities and integrate directly with BigQuery, Cloud Storage, and Google Workspace. |
| Not for | Teams that need full control over the voice synthesis pipeline (use ElevenLabs Conversational AI). Teams with very low call volume — the per-minute pricing pays back at scale, not for occasional use. | Teams not on Google Cloud — Vertex's value proposition is integration depth that doesn't transfer. Teams that want model flexibility — Vertex is Gemini-only. |
Our verdict on Retell AI
Clean SDK, predictable pricing, sub-second latency. The builder-friendly voice agent platform for teams that want production voice without owning the infra.
Full Retell AI review →Our verdict on Vertex AI Agent Builder
Google's enterprise agent platform on Vertex AI. Best for Google Cloud teams wanting Gemini-native agents with BigQuery integration. Less useful elsewhere.
Full Vertex AI Agent Builder review →Retell AI
What works
- Sub-second latency for natural-feeling conversation
- Built-in telephony — bring a phone number, plug in
- Function-calling support for CRM updates, calendar booking, etc.
- Predictable per-minute pricing scales linearly with volume
- Production-grade — used by hundreds of B2B teams in 2026
What doesn't
- Per-minute pricing adds up at very high volume
- Lock-in to Retell's voice stack
- Less flexibility than building on raw infrastructure
- Voice quality is good but not the best on the market
- Customer support response times vary
Vertex AI Agent Builder
What works
- Gemini's 1M+ token context window — the largest on the market
- Native integration with BigQuery, Cloud Storage, Google Workspace
- Grounding with Google Search built in (real-time web data)
- Google Cloud security, compliance, and IAM
- Free tier credits for new accounts make evaluation easy
What doesn't
- Gemini-only — no Claude, GPT, or Llama support
- Only makes sense if you're already on Google Cloud
- Slower iteration than Anthropic or OpenAI direct
- Documentation is dense and assumes Google Cloud familiarity
- Enterprise contract overhead at scale
Which to pick
We'd default to Retell AI (4.0/5 vs 3.5/5) for most builders. Pick Vertex AI Agent Builder if you fit its best-for case specifically: engineering teams on google cloud who want to build agents using gemini's long-context capabilities and integrate directly with bigquery, cloud storage, and google workspace.
Honest middle: most serious operators end up using more than one tool. If you're early in your AI agent journey, our five-question picker recommends a starting platform from your specific situation.
Common questions
Retell AI vs Vertex AI Agent Builder — which should I pick?
We rate Retell AI 4.0/5 vs 3.5/5 for Vertex AI Agent Builder. Retell AI wins for b2b teams deploying voice agents for outbound sales, customer support, or appointment booking. strong for builders who want a managed voice infrastructure without owning the telephony stack. — but pick Vertex AI Agent Builder if you fit its specific best-for case (Engineering teams on Google Cloud who want to build agents using Gemini's long-context capabilities and integrate directly with BigQuery, Cloud Storage, and Google Workspace.). See the head-to-head table above for the full breakdown.
Is Retell AI or Vertex AI Agent Builder cheaper?
Retell AI's pricing: Pay-per-minute usage: ~$0.07–0.10 per minute of voice conversation. Free tier with limited minutes. Volume discounts at enterprise scale. Vertex AI Agent Builder's pricing: Usage-based on Google Cloud: per-token Gemini model costs + Vertex AI infrastructure. Free tier credits available for new accounts. The right "cheaper" pick depends on usage volume and what's included — see the pricing row in the table above.
What's Retell AI best for?
B2B teams deploying voice agents for outbound sales, customer support, or appointment booking. Strong for builders who want a managed voice infrastructure without owning the telephony stack.
What's Vertex AI Agent Builder best for?
Engineering teams on Google Cloud who want to build agents using Gemini's long-context capabilities and integrate directly with BigQuery, Cloud Storage, and Google Workspace.
Why compare Retell AI and Vertex AI Agent Builder if they're different categories?
Retell AI is a voice ai agent and Vertex AI Agent Builder is a enterprise platform. The comparison still matters because builders evaluating one often consider the other for adjacent jobs. See the recommendation section above for how to think about the cross-category choice.
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