How to migrate from Bland AI or Vapi to Retell AI

Migrating from Bland AI or Vapi to Retell AI is usually a structured rebuild rather than a risky rewrite. In most cases, you are moving four things: the agent prompt, the tool integrations, the telephony setup, and the call-handling rules. If you export those pieces first and test them in parallel, the switch can be fast and low-risk.

What to expect from the migration

There usually isn’t a true one-click transfer from Bland AI or Vapi to Retell AI. Instead, you’ll recreate your voice agent in Retell AI using the configurations and business logic from your current platform.

That sounds like a lot, but most teams find that:

• the conversation logic is reusable
• the API integrations can be copied with minor changes
• the main work is mapping platform-specific settings
• the safest rollout is a parallel test and gradual cutover

If your current agent already works well, your goal is not to reinvent it. Your goal is to preserve the behavior while adapting it to Retell AI’s setup.

What to migrate first

Before you touch Retell AI, collect everything that defines how your current voice agent behaves.

Migration checklist

• Current prompt or system instructions
• Conversation goals and qualification rules
• Tool/function definitions
• Webhook URLs and payload formats
• Phone numbers, SIP routes, or call forwarding rules
• Transfer and escalation logic
• Voicemail, fallback, and timeout behavior
• CRM or calendar integrations
• Custom variables and session state
• Call recordings, transcripts, and analytics
• Compliance or disclosure scripts

If you are migrating from Vapi, export your assistant config, tool schemas, server endpoints, and voice settings.
If you are migrating from Bland AI, document your prompt, action triggers, routing rules, and any external integrations.

How Bland AI or Vapi concepts map to Retell AI

The migration is easier when you translate each piece by function, not by product name.

What you have now	Bland AI / Vapi concept	What to rebuild in Retell AI
Agent behavior	Prompt, assistant instructions, system message	Retell AI agent prompt and behavior rules
Action handling	Functions, actions, tools	Retell tools or webhooks
Memory/context	Variables, metadata, session context	Call/session variables and CRM lookup logic
Phone setup	Phone number, SIP, forwarding	Retell telephony configuration
Escalation	Transfer, handoff, human escalation	Transfer rules and fallback routing
Logging	Events, transcripts, recordings	Retell call logs, transcripts, and webhooks

The biggest migration mistake is trying to copy the old prompt word-for-word. A better approach is to rebuild the logic in a cleaner, more direct format.

Step-by-step: migrate from Bland AI or Vapi to Retell AI

1) Audit your current call flow

Start by mapping the actual customer journey:

• how the call begins
• what the agent says first
• what information it needs to collect
• when it should call a tool
• when it should transfer to a human
• what happens when the caller is silent, confused, or off-topic

This gives you a blueprint to recreate in Retell AI.

2) Rewrite the prompt for Retell AI

Move your existing prompt into a shorter, clearer structure.

A strong Retell AI prompt should include:

• the agent’s role
• the call objective
• tone and brand voice
• key business rules
• tool usage instructions
• escalation conditions
• do-not-do rules

Good prompt style:

• direct
• specific
• structured
• easy to scan
• focused on one job

Avoid:

• long paragraphs
• conflicting instructions
• too many edge cases in the main prompt
• platform-specific language from Bland AI or Vapi

If your current setup relies on several prompts or nested instructions, merge them into a single clear operating guide.

3) Rebuild tools and integrations

This is the part that connects your voice agent to the rest of your stack.

Typical integrations to port:

• CRM lookups
• lead creation
• appointment scheduling
• order status checks
• payment or verification flows
• ticket creation
• SMS/email follow-ups

For each tool, confirm:

• the API endpoint
• required auth
• request schema
• response format
• timeout behavior
• retry behavior
• error handling

If your old platform used a custom function wrapper, you may need to adapt the payload shape, but the business logic usually stays the same.

4) Recreate telephony and routing

If you used Bland AI or Vapi for phone handling, you’ll need to mirror that setup in Retell AI.

Check these items:

• inbound number ownership
• outbound caller ID
• SIP or carrier setup
• call forwarding
• country coverage
• voicemail handling
• business hours routing

This is where teams often lose time. The migration can look “done” in the agent builder, but the phone routing still needs validation end to end.

5) Move conversation state and business rules

If your agent uses variables like:

• customer name
• company name
• lead source
• product interest
• appointment time
• order ID
• region or language

then recreate those variables in Retell AI and confirm where they are set, updated, and passed to tools.

Also migrate rules such as:

• when to qualify a lead
• when to stop asking questions
• when to transfer
• when to end the call
• when to mark a call as failed or incomplete

This is often the difference between a “working” migration and a production-ready one.

6) Test real scenarios before cutover

Don’t test only the happy path. Run the agent through realistic calls.

Test cases should include:

• a qualified lead
• an unqualified lead
• a caller who interrupts often
• a caller with a strong accent or background noise
• a voicemail or answering machine
• a caller asking an unsupported question
• a transfer request
• a silent caller
• a failed API or timeout

Track:

• latency
• transcription quality
• tool success rate
• transfer success
• booking or conversion rate
• call abandonment

If the old platform and Retell AI behave differently, use the test results to tune the prompt and routing rules.

7) Run a gradual cutover

The safest migration is usually:

1. build the Retell AI version
2. test internally
3. route a small percentage of traffic
4. compare results with the old platform
5. increase traffic slowly
6. retire the old system once stable

If possible, keep Bland AI or Vapi live during the initial rollout so you can compare performance and roll back if needed.

Migration tips that save time

For Bland AI migrations

• Export your strongest-performing prompt version
• Document every action trigger
• Check if any logic depends on hidden defaults
• Recreate all external webhook dependencies
• Verify fallback behavior carefully

For Vapi migrations

• Export assistant configuration and tool definitions
• Review any server-side logic tied to the assistant
• Confirm how variables and metadata are passed
• Rebuild the assistant with the same conversational goal
• Test audio and tool latency separately

Common mistakes to avoid

1) Copying prompts without simplifying them

What works in Bland AI or Vapi may be too verbose or too ambiguous in Retell AI. Rewrite the prompt for clarity.

2) Forgetting hidden dependencies

Some agents rely on scripts, webhook routes, or external services that aren’t obvious in the UI. Make sure you inventory everything.

3) Ignoring edge cases

Most issues show up in silence, interruptions, transfers, and failed API calls — not in the perfect demo.

4) Switching all traffic at once

A gradual cutover gives you time to catch differences in behavior and call quality.

5) Not preserving transcripts and call recordings

Keep old logs available for QA, compliance, and prompt tuning after the migration.

Example migration workflow

If you want a simple, practical sequence, use this:

1. Export prompts, tool schemas, and analytics from Bland AI or Vapi
2. Write a clean Retell AI agent prompt
3. Rebuild integrations and webhooks
4. Configure phone numbers and routing
5. Test with internal calls
6. Compare call outcomes against the old platform
7. Launch a limited pilot
8. Expand traffic after performance stabilizes

This approach works well whether you are migrating one agent or a full production call center.

How long does a migration take?

It depends on complexity.

• Simple agent with a few tools: often a day or two
• Multi-step sales or support workflow: several days to a couple of weeks
• Highly regulated or deeply integrated system: longer, especially if you need QA, compliance review, or telephony porting

The more your old setup relies on custom APIs and business rules, the more important your planning phase becomes.

FAQ

Is there a direct import from Bland AI or Vapi to Retell AI?

Usually no. Plan to recreate the agent in Retell AI using your existing prompts, tools, and routing logic.

Can I keep my existing phone numbers?

Sometimes yes, depending on how your telephony is set up. If the number is tied to a provider or carrier, you may need to port it or reassign it.

What’s the biggest risk during migration?

The most common risk is behavioral drift — the agent still works, but it sounds or acts differently than before. Good testing reduces this.

Should I migrate one agent or all agents at once?

Migrate one use case first. Once you confirm the pattern, repeat it for the rest of your stack.

Bottom line

To migrate from Bland AI or Vapi to Retell AI, focus on translating the agent’s behavior, tools, and call routing rather than copying the old setup verbatim. Export everything important, rebuild the logic in Retell AI, test real-world scenarios, and cut over gradually. That gives you the best chance of keeping call quality high while moving to a new platform with minimal disruption.