ExpressLRS 4 does not talk to ExpressLRS 3
The two firmware projects under almost every FPV build changed generations this year. One of them now needs both ends upgraded at once.
What this is written from: Written from the official release notes of ExpressLRS 4.0.0 (6 February 2026) and 4.1.0 (17 July 2026), and of Betaflight 2025.12.1 (25 December 2025) and 2026.6.1 (2 August 2026), on GitHub, and RadioMaster's pricing notice of 2 July 2026, read on 29 September 2026. Not from flying them.
The upgrade that breaks the link
ExpressLRS is the control link in nearly every new build, and version 4.0 arrived in February. The line in its release notes that matters most is short: a 4.x transmitter does not link with a 3.x receiver. Radio and receiver move to the new generation together, or not at all.
That sounds like a footnote until you own more than one quad. Flash your radio's module to 4.x and every receiver still on 3.x stops binding until you update it too, and a whoop you last flew in spring is the one you will forget.
ExpressLRS 4.0 and 4.1, the parts that affect buying
From the release notes. Both ends of the link are affected.
| Link compatibility | 4.x does not link with 3.x |
|---|---|
| Older hardware | STM32-based hardware is no longer supported, including R9M |
| Antenna mode | Diversity or Gemini chosen automatically |
| Arming | New optional method that frees channel 5 (needs EdgeTX 2.11 or later) |
| DJI air units | A receiver output that can wake a DJI unit from low-power mode |
| 4.1.0 (July) | More aggressive power stepping, bind phrase from the handset |
Betaflight changed its numbers, and its app
Betaflight moved from 4.x version numbers to year and month: 2025.12 in December, 2026.6 in August. It is configured through the web app at app.betaflight.com rather than the old desktop configurator. 2025.12 added altitude hold and position hold; 2026.6 adds an autopilot mode that flies waypoint missions, with GPS rescue rebuilt as one of them.
None of that changes what bolts to what. It changes what a flight controller is worth: position hold and missions need a GPS or an optical-flow sensor, and a board with no spare serial port for one is a board that cannot use the headline feature of the release it runs. That is a fair question to ask of a stack before you buy it.
Where this goes next
- Why a radio will not bind Protocol, band and the serial link to the flight controller.
- Receivers, checked against radios Which receivers speak which protocol and band.
What Buildlas checks for you here
Every rule is published, with what it reads and what it does when a specification is missing.