This is our final changelog of 2025, and we’re focused on making teams faster today, and setting you up to ship with more control heading into 2026.

The headline of this release is the new Agent Editor v2: a redesigned agent workspace that puts every setting, action, and flow decision in one place.

Right behind it is a major improvement to call quality with Synthflow STT, a multilingual transcription upgrade that makes non-English calls (especially German and Spanish) far more accurate.

And because faster building only matters if shipping stays safe, we’re also launching Agent Versioning, plus GPT-5.2 availability and phone number + routing reliability improvements.

Keep scrolling for the full breakdown!

P.S. Thanks for building with us this year, and happy new year from all of us at Synthflow.

Introducing Agent Editor v2: Build Faster from a Single Screen

Agent Editor v2 is a comprehensive redesign of the Synthflow platform that brings all agent settings directly into the agent view. With Agent Editor v2, settings that used to be spread across the platform are now accessible directly inside the agent view, making iteration noticeably faster.

You’ll find a redesigned experience across custom actions, agent settings, flow designer, and more, all in a more compact, modern, enterprise-ready interface. It works seamlessly for both single-prompt and flow designer agents.

Agent Editor v2 is available via a self-serve preview switcher, so you can toggle between UI versions and test it before fully committing.

No more bouncing between pages. Everything you need to build, tune, and manage your agents now lives in one place.

Agent Versioning: Built in Snapshots, Diffs & Rollbacks

Agent Versioning gives you complete control over how your agent changes over time. Every time you publish, Synthflow creates a new version, so you can move fast without losing track of what changed.

With Agent Versioning you can:

• Create and manage versions: Publish changes to generate a new version with a clear diff showing exactly what changed across prompts, settings, and flow designer nodes.

• Export versions as JSON: Back up agent configurations to GitHub or your own storage for safekeeping and auditability.

• Restore previous versions: Roll back to any prior version when needed—ideal for testing, troubleshooting, or reversing an unwanted change.

• Track version history: View the complete timeline of edits with version numbers visible throughout the platform.

Custom Actions v2: More Power, Control & Speed

More powerful, easier to configure, and significantly faster to ship.

Custom Actions have been redesigned inside the new Agent Editor v2 to make integrations quicker, cleaner, and harder to mess up. The new system is fully backwards compatible, while introducing major workflow improvements.

Key upgrades include:

• System Variables: Instantly access call data (like call_id, user_phone_number, from_phone_number, and more) by typing < in any URL, header, or body field—no extra configuration required.

• Auto-Detection: Input variables are automatically detected from your JSON using <variable_name> syntax, with intelligent autocomplete and auto-save when mapping.

• Smoother Workflow: Configure actions faster in Agent Editor v2, use before-call action data anywhere in your flow, and map variables with far less manual effort.

Synthflow STT: Improved Non-English Language Support

We’ve deployed a new speech-to-text model, Synthflow STT, to solve a critical pain point: reliably capturing phone numbers, names, and invoice/reference numbers in German, Spanish, and other non-English languages.

Internal testing shows this model performs markedly better than our previous provider—especially on the kinds of high-stakes details that make or break real deployments.

If you have customers running German or Spanish agents, we strongly recommend testing (and switching to) Synthflow STT. It’s a game-changer for accuracy.

GPT-5.2 Now Available

GPT-5.2 is now available in the Synthflow platform.

A quick note from our testing: GPT-5.2 can be more verbose than teams expect. Before switching a production agent, use the Test Center to validate behavior and confirm your agent remains backwards compatible.

If you want to be extra safe, run Simulations to compare model behavior across the same real caller scenarios before you roll anything out.

Phone Number Management Improvements

Phone number management has been significantly upgraded across performance and API capabilities for faster operations, better reliability, and improved error handling.

Performance Improvements

• Attach/detach phone numbers: Much faster operations with reduced latency.

• List phone numbers: Significantly improved endpoint performance.

• Import custom numbers (Enterprise only): Faster imports with clearer error messaging.

Other Updates

A set of additional improvements shipped this week:

• Improved voicemail detection: Fixed the edge cases where the audio from the user was not being captured and this was causing the system to misclassify some voicemail samples.

• Concurrency adjustments: With improved concurrency management, agents can now answer calls even faster.

• Telephony infrastructure: New edge/router setup for more reliable, efficient call routing—plus improved call tracking and external ID traceability.