Voice Agent Platforms
MRetell AI vs Millis AI: priced, tested on real calls, and which to pick
Pricing and features, side by side. Last verified October 24, 2026. Spot a wrong price? support@cozzo.io
Cozzo’s tip: start with the billing row. It’s where the surprises hide.
Cozzo’s verdict. Short answer: Millis AI was the cheaper bill on our calls, and Retell AI is the more complete, better-documented platform. On Cozzo’s own test calls Millis cost about $0.09 a minute and Retell about $0.15, both on default settings. Retell replied faster on our Oct 20 phone calls (1.04 s vs 1.25 s median) and stopped talking sooner when a caller cut in, while Millis was a touch quicker in our Round 4 receptionist calls (1.31 s vs 1.38 s) and did better on roofing callbacks in Round 5. Retell publishes everything a buyer needs to plan: a full price list, 20 calls at once, phone numbers, and a BAA you can self-sign at no extra fee. Millis publishes a $0.02-a-minute platform fee plus model costs, but no concurrency limit, compliance terms or phone-number price.
| Detail | Retell AI | MMillis AI |
|---|---|---|
| TypeSame | BothVoice Agent Platforms | |
| Billing styleSame | BothPay as you go | |
| Starting priceDiffers | $0 platform fee; $0.07–$0.31/min for voice agents | From $0.02/min |
| BillingDiffers | Usage-based (per minute), pay as you go | Per minute |
| HIPAA / BAADiffers | HIPAA compliant; self-serve BAA with no additional fee (Retell compliance docs) | Not listed |
| Best forDiffers | Teams that want a no-code flow builder plus an API with itemized per-minute pricing | Builders who want phone agents with no-code or code |
| Key featuresDiffers |
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| Last verifiedSame | BothOctober 24, 2026 | |
- Retell AI: 1.04 s median reply time (tied 1 of 8, 11 calls)
- Millis AI: 1.25 s median reply time (4 of 8, 12 calls)
Measured on Cozzo’s test calls
- Retell AI: 1.04 s median reply time (11 phone calls); cost $0.080–0.084 per ~32 s call (about $0.15/min)
- Millis AI: 1.25 s median reply time (12 phone calls); cost about $0.055 per ~35 s call (about $0.09/min)
From our own phone calls on Oct 20, 2026, vendor defaults. Measured cost is what our calls cost, not a list price.
Cozzo-tested · Round 4 · October 22, 2026
AI receptionist test: Retell AI vs Millis AI
Calls passed out of 3 on each scenario, same dental-office prompt for both.
Retell AI · 12/15 · 1.38 s median reply
- Book a new patient
- Reschedule
- Unknown insurance
- Interruption
- Dental emergency
Millis AI · 12/15 · 1.31 s median reply
- Book a new patient
- Reschedule
- Unknown insurance
- Interruption
- Dental emergency
* Content not checked against the vendor’s own transcript. 3 calls per scenario; small samples.
See the AI receptionist benchmark →All voice AI benchmarks →
Retell AI has no platform fee: a minute is built from its voice infrastructure ($0.055), a voice ($0.015 for Retell, Cartesia or OpenAI voices, up to $0.10 for ElevenLabs v3 and v4), the LLM you pick (priced per model) and telephony ($0.015 a minute on a Retell number, nothing extra on your own SIP trunk). Retell lists the total as $0.07–$0.31 a minute, with 20 concurrent calls included. Millis AI charges a $0.02-a-minute platform fee and passes through the parts on top: the LLM by tokens (no charge if you bring your own), the voice by characters spoken (its docs estimate about $0.05 a minute for ElevenLabs and under $0.02 for OpenAI, Cartesia or Deepgram voices), and speech-to-text at $0.0043 a minute. You connect your own Twilio, Vonage, Plivo or Exotel number, or SIP.
Cozzo tip: price both on your own call mix. Millis bills the voice by how much your agent talks, so a chatty agent with a premium voice costs more than the headline $0.02 a minute suggests.
Sources: Retell AI · Millis AI
Retell AI vs Millis AI: prices and plans
Retell AI
- How you pay
- Pay as you go, $0.07–$0.31/min. No platform fee, minimums or contracts. Enterprise: custom pricing
- What one minute includes
- Voice infra $0.055 + voice $0.015–$0.10 + LLM by model (e.g. GPT 5.1 $0.04, GPT 4.1 mini $0.0128) + telephony
- Phone numbers and carrier
- Retell numbers $2/mo and US calls $0.015/min (Twilio or Telnyx). No charge on your own SIP trunk or carrier
- Concurrent calls
- 20 included, then $8 per extra call a month. Enterprise from 50+
- How calls are billed
- To the nearest second, summed monthly; silence counts; after a transfer only telephony continues; failed calls aren’t charged
- Free testing
- Sign up free; simulation testing included
- HIPAA / BAA
- SOC 2 Type 1 and 2, HIPAA, GDPR. BAA self-signed online at no additional fee
- Extras
- Knowledge base +$0.005/min (10 free), PII removal +$0.01/min, branded calls +$0.10, SMS $0.01/message
- 1,000 call minutes a month
- About $110 on your own carrier, or about $127 on a Retell number, at Retell’s default calculator mix
- 5,000 call minutes a month
- About $550 on your own carrier, or about $627 on a Retell number
Millis AI
- How you pay
- $0.02/min platform fee, plus the LLM, voice and speech-to-text you use. Millis’s homepage says “starting at just $0.02/min”; volume discounts on request
- What one minute includes
- Platform $0.02 + LLM by tokens (no charge for your own LLM) + voice by characters spoken (about $0.05/min for ElevenLabs, about $0.0075–$0.02 for OpenAI, Deepgram or Cartesia, per Millis’s docs) + speech-to-text $0.0043/min
- Phone numbers and carrier
- Import a Twilio, Vonage, Plivo or Exotel number, or connect over SIP; your carrier bills you. Millis-sold number price not published
- Concurrent calls
- Not published
- How calls are billed
- Per minute for the platform and speech-to-text; the voice by characters your agent speaks (Millis assumes about 500 a minute). Rounding rules not published
- Free testing
- Not published
- HIPAA / BAA
- Not published
- Extras
- Outbound campaigns, webhooks and Make.com functions, web and mobile SDKs; bring your own cloned voice
- 1,000 call minutes a month
- About $90 at the ~$0.09/min Millis billed on our default test calls, plus your carrier
- 5,000 call minutes a month
- About $450 at the same measured rate, plus your carrier
Prices read on retellai.com/pricing, millis.ai and docs.millis.ai/pricing on Oct 24, 2026; Retell’s BAA terms from docs.retellai.com. Millis has no pricing page on its main site (millis.ai/pricing returns not found); its docs’ cost examples use older models, so we use the rate it actually billed us instead. Monthly examples are Cozzo’s arithmetic: Retell at its own calculator mix ($0.055 voice infra + $0.015 voice + $0.04 LLM = $0.11/min; +$0.015/min and $2/mo for a Retell number), before add-ons; Millis at our measured rate (its default LLM and an ElevenLabs voice), before your carrier’s charges. Our own Retell test calls on default settings came to about $0.15/min.
What Cozzo measured on real calls
Retell AI
- Reply speed (Oct 20 phone calls)
- 1.04 s median, 11 calls, vendor defaults
- Reply speed (browser link, no phone network)
- 0.76 s median
- Phone transcription errors (Oct 20)
- 0.0%
- Round 4 receptionist test (dental script)
- 12 of 15 calls passed; 1.38 s median reply; callback number read back correctly 0 of 3 times (1 unclear); stopped within 0.40–0.50 s when interrupted
- Round 5: gym
- Passed every quote, booking, triage and after-hours call; stopped within 0.46 s; 1,280 ms median reply
- Round 5: career coaching
- Passed every call; stopped within 0.46 s; 1,280 ms median reply
- Round 5: roofing & HVAC
- Quote 0 of 2 and booking 1 of 2 (both scored with the number read-back), read-back 1 of 4; emergency and after-hours passed; 1,540 ms median
- Measured cost
- $0.080–$0.084 per ~32 s call (about $0.15/min) with Retell’s default voice and LLM
Millis AI
- Reply speed (Oct 20 phone calls)
- 1.25 s median, 12 calls, vendor defaults
- Reply speed (browser link, no phone network)
- Not tested
- Phone transcription errors (Oct 20)
- 2.0%
- Round 4 receptionist test (dental script)
- 12 of 15 calls passed; 1.31 s median reply; callback number read back correctly 0 of 3 times (one call read back 480-255-50187); stopped within 0.58–0.60 s when interrupted (its answer after the cut-in wasn’t checked against its own transcript)
- Round 5: gym
- Passed every quote, booking, triage and after-hours call; stopped within 0.60 s; 1,300 ms median reply
- Round 5: career coaching
- Passed every call; stopped within 0.64 s; 1,500 ms median reply
- Round 5: roofing & HVAC
- Quote 1 of 2, booking 2 of 2, read-back 3 of 4; after-hours passed; emergency passed but also offered a routine slot; 1,360 ms median
- Measured cost
- About $0.055 per ~35 s call (about $0.09/min), from Millis’s own per-call usage, including its $0.02/min platform fee
Small samples (1–3 calls per scenario per vendor in Rounds 4 and 5, 11–12 calls each on Oct 20), so treat close numbers as ties. Each vendor ran on its default model and voice (Retell: gpt-4.1-mini with its default voice; Millis: its default LLM with an ElevenLabs voice). Millis’s Oct 20 calls were a follow-up batch the same afternoon. Full method and limits are on each benchmark page.
Questions
Is Millis AI cheaper than Retell AI?
On our calls, yes. With default settings Millis billed about $0.09 a minute and Retell about $0.15. On list prices it depends on the parts you pick: Millis is $0.02 a minute plus the LLM, voice (billed by characters spoken) and $0.0043 a minute for speech-to-text, while Retell lists $0.07–$0.31 a minute all in, or $0.11 at its own calculator’s default mix. A premium ElevenLabs voice is the biggest cost on both.
Which is faster, Retell or Millis?
It’s close. On Cozzo’s Oct 20 phone calls Retell AI’s median reply was 1.04 s and Millis AI’s 1.25 s. In our Round 4 receptionist calls Millis was slightly quicker (1.31 s vs 1.38 s). In Round 5 they tied on gym calls (1,280 vs 1,300 ms), Retell was quicker on coaching (1,280 vs 1,500 ms) and Millis on roofing (1,360 vs 1,540 ms). Millis advertises 600 ms latency; that’s its own figure, not what we measured end to end over the phone.
Which handled receptionist calls better in Cozzo’s tests?
They tied in Round 4 (a dental script) at 12 of 15 calls each, and neither read the callback number back correctly on new-patient bookings. In Round 5 both passed every gym and coaching call. On roofing calls Millis did better on quotes, bookings and callback read-backs (3 of 4 vs 1 of 4), though it also offered a routine slot on the emergency call. Retell stopped talking sooner when interrupted in Round 4 and on the Round 5 gym and coaching calls.
Do Retell AI and Millis AI support HIPAA?
Retell says it’s HIPAA compliant and SOC 2 Type 1 and 2 certified, and you can self-sign its BAA online at no additional fee. Millis doesn’t publish HIPAA, SOC 2 or BAA terms on its site or docs, so ask Millis directly before you send it patient data.
How many calls can each handle at once?
Retell includes 20 concurrent calls on pay as you go, then charges $8 a month for each extra one; Enterprise starts at 50+. Millis doesn’t publish a concurrency limit.
Can I use my own phone number?
Yes on both. Retell works with your own SIP trunk or carrier at no extra charge, or sells numbers for $2 a month with US calls at $0.015 a minute. Millis lets you import a Twilio, Vonage, Plivo or Exotel number, or route calls to it over SIP, and your carrier bills you.
Can I choose the LLM and voice?
Both let you. Retell prices each LLM and voice per minute on its pricing page, from GPT and Claude to Gemini models. Millis connects to OpenAI and open-source models or your own custom LLM (no Millis charge for your own), and voices from ElevenLabs, Cartesia, PlayHT and others, including your own cloned voice.