Announcing ThunderPhone

Today, we’re proud to announce the public launch of ThunderPhone, which makes it easy to automate phone calls with AI. With a completely different integrated architecture from other phone AI platforms, ThunderPhone is able to achieve much higher performance, lower cost, and fewer integrations headaches. ThunderPhone supports inbound and outbound calls in dozens of languages and is fully HIPAA and GDPR compliant.

Three Tiers of Phone Agents

ThunderPhone offers 3 tiers of phone agents:

1. Zap, the cheapest system on the market, to our knowledge, at 2 cents per minute. Zap is a bit slow, but can handle many use cases at rock-bottom pricing.
2. Spark, our mid-tier offering at 6 cents per minute. Spark is lightning-fast and smart enough for many use cases.
3. Bolt, our most advanced offering, from 12 cents per minute. Bolt dynamically routes between fast AI models and slower but much smarter models to keep conversations feeling responsive while offering an intelligence level unmatched by any other offering we’ve seen on the market.

(Pricing is a flat rate per minute, with surcharges for extra-long prompts and Pro voices.)

The Integrated Advantage

Other phone AI platforms limit the performance of their systems by enforcing a 3-step structure to their systems:

1. One transcription model, which turns the user’s voice into text.
2. One LLM, which processes the user’s text and outputs a response.
3. One TTS model, which turns the response text back into audio.

Most of them also push engineering work onto their users by forcing users to pick which models they want to use, as well as configuration options like denoising and responsiveness parameters.

We’ve taken a different approach: we’ve configured what is in our opinion the best possible stack with the models of today, and made it ready to use without complex configuration effort. Our system uses many models at the same time, with the system routing between them intelligently depending on the flow of the conversation. This includes:

• Combining multiple transcription models, some faster than others, some more accurate than others, to balance speed with accuracy and cover for each others’ mistakes.
• Combining audio-input LLMs, which can have lower general intelligence but better audio understanding, with text-only LLMs, which can make mistakes from inaccurate transcripts but are often smarter.
• Combining fast but stupid LLMs, which can generate quick responses, with much smarter but slower LLMs, which can run in the background and make sure the AI is following its prompt and responding to what the user says correctly.
• Combining commercial models from top providers including OpenAI and Google, which offer the highest intelligence available today, with a wide assortment of open-source models, which often offer better speed at lower cost.
• Using multiple models simultaneously to classify and eliminate background noise, side conversations, and other distracting noise which can otherwise derail a conversation.

These components and more are orchestrated in different ways in Zap, Spark, and Bolt — optimizing Zap for cost, Spark for speed, and Bolt for intelligence, while minimizing the drawbacks of each as much as possible. All three systems share benefits like incredibly accurate understanding of what users say, even with proper nouns and spelling.

We find that this tightly-integrated architecture gives our system far higher performance at lower cost than the rigid 3-step approach offered by other vendors. In line with Clay Christensen’s modularity theory, it’s still early days in voice AI, and it’s still more valuable to maximize performance with an integrated architecture than it is to maximize customizability with a modular architecture.

Optimized Decisions

And as far as customizability goes, we are against it! Most of today’s phone AI platforms force users to navigate endless choices, from the exact models used, to ultra-detailed parameters like how quick the AI is to interrupt the user.

In our opinion, it is OUR job to optimize these choices behind the scenes so that ThunderPhone’s users can focus on what they are good at and not worry about detailed voice AI configuration. We see ourselves as a sort of Squarespace, making it easy for our users to set up phone agents at the absolute highest performance possible with today’s models, without lifting a finger.

We also believe in competitive pricing. All of our service levels are priced at between 10 and 25 per cent gross margin, meaning that even if you rebuild ThunderPhone from scratch, you’ll only be saving a penny or two a minute at most, and likely less, since it would be hard to duplicate some of the cost-saving optimizations we’ve made behind the scenes. This also means that no other phone AI platform can beat ThunderPhone on price at any level of performance offered.

Ease of Use

ThunderPhone is also incredibly easy to use, whether you’re setting up a new phone agent, or migrating from a different platform or from a custom stack. All that it’s necessary to do to set up a phone agent on ThunderPhone is:

1. Decide whether you want to use Zap, Spark, or Bolt.
2. Choose a voice.
3. Give us your prompt. No multi-prompt agents needed! If your prompt is too complicated for Zap or Spark, upgrade to Bolt, which can handle even complex use cases with a single prompt.
4. Connect software integrations (any endpoint, or native n8n integration) with an incredibly easy-to-use wizard.
5. Connect your VoIP with an incredibly easy-to-use wizard.

All of this typically takes 10 minutes or less.

Voice Tiers

ThunderPhone supports 3 tiers of voices:

Pro HD and Pro Turbo support the exact same voices and languages, so it’s easy to switch between them to trade off quality and speed.

All voices offered on ThunderPhone have been vetted to hallucinate essentially never, so you can be confident your system will not say crazy things to the user.

ThunderPhone is fully compliant with HIPAA and GDPR, and we will sign and provide BAAs and DPAs upon request.

Our Story

We’re a team of Stanford AI Lab and Y Combinator alumni that have been working on voice AI since 2024. Originally, our focus was on Flux Interpreting, which translates phone calls between languages. But after being repeatedly asked by customers to automate phone calls for their businesses instead of just translating them, we shifted focus to what is now ThunderPhone.

The Problem with Existing Platforms

Initially, we began by building phone agents for customers on other company’s phone AI platforms. We tested just about every phone AI platform on the market, but unfortunately found them lacking, especially when it came to:

• Audio understanding: The limitations of only having one transcription model to turn the user’s audio into text meant that the AI would often “mishear” the user, especially with proper nouns, uncommon words, and spellings.
• Instruction following: Having a single fast LLM doing the actual “brainwork” behind the call meant that the AIs would often struggle to follow instructions correctly and go off the rails.
• Difficult integrations: The platforms we tried made it very hard to connect to external software, generally making us type in extensive JSON configurations for tool calls and bash against them repeatedly with little to no feedback until they suddenly started working.
• Price: Existing platforms generally charged an arm and a leg: usually 10 cents a minute or more for so-so performance.

Building Our Own Stack

When we signed a deal to implement a sales call use case for an enterprise client, we were forced to build our own custom stack to meet their needs. This use case was demanding: unlike customer support, where callers are largely at the business’s mercy, sales callers are quick to hang up.

Call quality must be top-notch to make the sale instead of losing the lead. This meant handling extensive proper nouns and spellings, including names and addresses, that are hard for standard transcription models to get right. To nail this use case, we built what is now ThunderPhone.

Along the way, we kept meeting people in the San Francisco voice AI community who were building vertical phone agent companies — for veterinarians, truck drivers, and more. Surprisingly, most of them had the same opinion: existing platforms were good enough for demos, but not for production.

Shockingly, many if not most of our friends in vertical voice AI companies were actually “rolling their own” stacks... This made no sense to us — it’s really the equivalent of web startups in the 90s having to host their own web servers on a server in their closet.

With that insight, we realized that it was time to turn our phone AI system into a platform that anyone could use.

Vertical voice AI companies and consultants should be able to focus on meeting the needs of their target market with their industry-specific expertise — not on intricately engineering the underlying AI and phone technology! That’s what we’re launching today with ThunderPhone.

It’s been a long road to get here! Apologies to everyone who’s signed up with us since last April and is still waiting for access: what we thought would be a quick sprint to finish the job turned out to be a multi-month odyssey figuring out how to weave together the models available today into a system that’s as robust as possible.

But now we’re live at last — give it a try and see what you think!

While we’ve worked out the major kinks, there are sure to still be bugs in the system. If you find any issues, please email alex@thunderphone.com and I’ll see that it gets fixed for you ASAP. Let me know if you have any feature requests as well, and we’ll make those happen for you as soon as we can as well.

And if you have more custom needs, such as custom implementation and integration support, compliance beyond regular HIPAA and GDPR, SLAs, and custom feature requests, we’re happy to talk about an enterprise deal. Reach out at alex@thunderphone.com and we’ll talk about your needs and if we can help.

And more generally: our commitment to you is that it is OUR job to make sure that ThunderPhone works out of the box with minimal effort from you, and handles your business’s calls as perfectly as it is possible to do with today’s AI, within the limits of whichever price point you choose, Zap, Spark, or Bolt. Give us a try, and we’re excited to show you what ThunderPhone can do.

Let us know what you think, and thanks for your support!