Zeus
Zeus builds, tests and tunes your voice agents.
Think Claude Code for your phone calls. Tell it what your calls should do, and it picks the models, writes the prompt, connects your phone system, tests on simulated calls and keeps improving from live calls.
We miss calls after 6pm. Book service visits, and send anything about a gas smell straight to the on-call tech.
Plan
- CreateAgent from your notesBooking flow, service area, gas-smell escalation
- ConnectYour number and calendarForward after-hours calls, book into your scheduling system
- Test40 simulated callersNoisy lines, angry callers, a gas smell at 2am
- ImproveWatch live callsFlag problems, propose A/B tests
Why Zeus
Coding agents are great at code. Not at calls.
Claude Code and Codex are great at most software engineering. But they’re less good at voice agents, for three reasons:
Little real call audio
They learned mostly from text and code. The audio they saw comes from places like YouTube, not from live calls to a business.
They believe the marketing
Best practices about AI phone calls are scattered across the internet, next to plenty of misleading claims. Coding agents take those claims at face value.
They can’t run a call
Code runs or it doesn’t. A coding agent can’t place a real or simulated call out of the box, and it’s bad at spotting what went wrong in one.
What Zeus has instead.
Four sources of signal, so Zeus can change an agent and confirm it works, the way a coding agent runs the tests before it calls code done.
Evals on real calls, not vendor claims
We test every model for every part of the stack on data from real calls, and track the trade-offs as new models ship.
Two years of know-how
What we learned tuning voice agents by hand for real businesses, built into Zeus as prompting, guardrails and tools.
- Which voice to trust with phone numbers and spelled names
- When a turn needs the thinking model
- How to word a transfer so callers stay on the line
Call tools
Zeus simulates calls in hard situations and spots real issues in production calls. That gives Zeus the signal it needs to keep improving performance.
60 of 60 simulated and replayed calls pass. 2 bookings recovered.
Your own calls
Zeus learns from how your conversations actually go, and backtests every new configuration against your past calls before it proposes it.
Create
Start from what you have.
However your calls work today, Zeus can start there.
Call-center recordings
Zeus listens to how your best people handle calls and builds from that.
Scripts and SOPs
Upload what your team already follows.
Talk to Zeus
Describe your business. Zeus asks what it needs to know.
Write it yourself
Hand-write the prompt, and edit anything Zeus writes.
One-click import
Move agents from Vapi, Retell, ElevenLabs or Bland. Zeus handles the import end to end.
Connect
The annoying setup, done for you.
SIP trunks, VoIP numbers and software integrations are where voice projects stall. Zeus walks through them with you and checks that each step works.
- Phone systems. Bring your carrier over SIP, or buy a number in a minute.
- Transfers. Warm, cold and whisper transfers to the right person.
- Integrations. Your CRM, calendar or any API, with the schema worked out for you.
Our numbers are on our own carrier. Can we keep them?
- Trunk reachable
- Test call answered
- Caller ID passed through
Test
Find problems before your callers do.
Zeus tests every change on calls that haven’t happened yet, and on calls that already did.
Text and audio simulations
Catch problems in simulated calls before real callers run into them.
Replay your past calls
Every new version runs against real calls you’ve already had.
Turn mistakes into evals
Flag problems on past calls and test future agent configurations against them.
Improve
Callers keep hanging up when we ask for their policy number.
Example. Simulated and backtested before any live traffic.
Zeus watches your live calls.
It spots where calls go wrong, works out why, and proposes a fix as an A/B test against the goal you care about. You see the calls behind every suggestion.
- Hang-ups, loops, wrong transfers and missed bookings
- Fixes tested on simulated and past calls first
- Results measured against your funnel, not a vibe
Ship
Change live agents safely.
Every change is a version. Run versions side by side, split traffic between them, and keep the one that wins on your goals.
Every change saved. Roll back in one click.
Try a new prompt, voice or model next to the current one.
Send a slice of calls to the variant, from 1% to all of them.
Bookings, sales, resolved issues. Whatever counts for you.
Autonomy
You decide how much Zeus does on its own.
Have it ask before every change, or let it fire away. Change your mind any time.
Use it your way
Zeus lives in the web app. Its tools work anywhere.
Zeus itself runs in the ThunderPhone web app. Rather work in your own coding agent? Plugins, our MCP server and the API give it many of the same tools Zeus uses.
The full Zeus
Chat, simulated calls, live-call review and A/B tests in one place.
Claude Code and Codex
Your coding agent builds and tests agents with ThunderPhone’s tools, many of them the ones Zeus uses.
Any MCP client
Connect any agent to our MCP server.
Full control
Build and run agents from your own code.
Tell Zeus what your calls should do.
Zeus is free for now. Calls start at 2¢ a minute.