ExpressLRS 4.x vs 3.x: compatibility, changes and who should update

Contents

1. The one rule: 4.x and 3.x never talk
2. ExpressLRS version timeline
3. Can your hardware run ELRS 4?
4. What changed in 4.0
5. What changed in 4.1
6. Should you update? Decision box
7. If you update: the safe order
8. Staying on 3.x: what you need to know
9. FAQ

Researched from the ExpressLRS and Betaflight release notes, the ExpressLRS docs and RadioMaster's and BetaFPV's product pages; sources checked on the date shown above. We have not bench-tested ELRS 4 on our own hardware.

Versions this page covers

(checked October 14, 2026)

Line	Version	Released
ExpressLRS 4.x (current)	4.1.0	Jul 17, 2026 github.com
ExpressLRS 4.x	4.0.1	May 12, 2026 github.com
ExpressLRS 3.x (maintenance)	3.6.4	Jun 8, 2026 github.com
Betaflight	2026.6.2	Sep 16, 2026 github.com
ExpressLRS Configurator	1.8.3	Jul 22, 2026 github.com

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This page helps you decide. Flashing steps are in our ELRS firmware update guide, binding in how to bind an ELRS receiver, and more in the ExpressLRS hub.

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The one rule: 4.x and 3.x never talk

The ExpressLRS docs give the general rule: "The first number in the Version string should match between a TX Module and a Receiver." expresslrs.org

The 4.0.0 release notes apply that rule to the new line: "Not compatible with ExpressLRS 3.x.x, 2.x.x, or 1.x.x." They also say the new over-the-air (OTA) protocol "is incompatible prior versions and will not connect at all (theoretically)." github.com

There is no 3-to-4 "compatibility mode," whatever some blogs say. Neither the 4.0.0 nor the 4.1.0 notes mention a fallback github.com github.com. Within 4.x, mixing versions is fine: 4.1.0 is "Compatible with all hardware running any ExpressLRS 4.x version" github.com.

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Sources: ExpressLRS 4.0.0 notes github.com; Betaflight 2026.6 notes betaflight.com.

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ExpressLRS version timeline

Both lines are maintained in parallel, so 3.6.4 came out after 4.0.1.

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Dates are from the GitHub release pages github.com github.com.

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Can your hardware run ELRS 4?

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ESP-based 2.4 GHz TX modules and receivers

Most current UART receivers and TX modules (including internal radio modules) are ESP-based with an SX1280 chip and run either line. If you're on 4.0.0, update. The 4.0.1 notes are addressed to "All users on 4.0.0, especially those with SX1280 (2.4GHz) based receivers", and their SX1280 fix reportedly cures random failsafes and reconnection failures github.com. 4.1.0 is the later 4.x release github.com.

LR1121 / dual-band gear

LR1121 hardware gains the most from 4.x. The 4.0.0 notes say the new dynamic power model "majorly improves dynamic power for LR1121 systems", and the new packet modes are listed under "Expanded packet modes for LR1121" github.com.

STM32 hardware (dropped)

The 4.0.0 notes say: "Support for STM32-based hardware has been removed, including all R9M hardware, your ExpressLRS PP, and Ghost devices." github.com The ExpressLRS docs add the Happymodel ES915 TX and RX, early NamimnoRC Flash and Voyager, FrSky R9, and SIYI and ImmersionRC hardware expresslrs.org. If you fly any of it, your setup stays on 3.x until you replace it.

Built-in SPI receivers (whoops and AIO boards)

An SPI receiver runs ExpressLRS code inside the flight controller firmware, so its version comes from Betaflight: "You cannot use the ExpressLRS Configurator to update these FCs." expresslrs.org

Betaflight 2026.6 added ELRS V4 for SPI receivers, but not by default: "ELRS V3 is the default protocol when flashing new firmware, and is not compatible with ELRS V4 transmitters." You get V4 by setting ELRSV4 in the flasher's build flags, and that build no longer works with V3 transmitters betaflight.com.

The ExpressLRS docs lag behind: on October 13, 2026, the binding page (footer date October 4, 2024) still said "SPI-based Receivers on Betaflight 4.4.0 and newer will only sync or bind with ExpressLRS 3.x firmware" expresslrs.org. For 2026.6 ELRSV4 builds, the newer Betaflight notes take priority.

So a whoop on a default Betaflight build won't bind to an ELRS 4 radio. The 2026.6 notes don't say whether older builds can do V4, and the ExpressLRS SPI page only covers 2.x and 3.x expresslrs.org. Don't assume they can.

Reflashing Betaflight can reset your settings, so run diff all in the CLI and save the text first; the 2026.6 flasher can also back up and restore around a flash betaflight.com. See our Betaflight update guide.

Check which receiver your whoop has. BetaFPV says the current Meteor75 Pro has "Serial ELRS 2.4G instead of SPI ELRS 2.4G" compared with the previous version betafpv.com. A serial (UART) receiver's ELRS version comes from its own firmware, not Betaflight. See our BetaFPV Meteor75 Pro page.

Radios with internal ELRS (Pocket, Boxer, TX16S)

The internal module is an ELRS TX like any other, so it has to match your receivers. Official sources don't say which ELRS version a new radio ships with today. RadioMaster's Pocket product page names "ExpressLRS ISM FW" and "ExpressLRS CE EU domain LBT FW" without a version number radiomasterrc.com, and its firmware page only lists 2023 factory files (ExpressLRS 2.8.4 for Boxer and TX16S) radiomasterrc.com.

Check the version line near the bottom of the ExpressLRS Lua script; it shows firmware version and regulatory domain expresslrs.org. Our Pocket setup guide walks through it.

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What changed in 4.0

Channel mapping and arming

This change can affect safety, so read it even if you skip the rest.

• "Fullres packet modes users in 8ch and 12ch mode will find CH9 or CH13 missing, and Arm moved to CH14." github.com
• 8ch and 12ch modes used to generate 9 or 13 channels; now "fullres modes no longer "skip" CH5" and "CH5 is always a full channel." github.com
• An optional alternative arming method "requires EdgeTX 2.11.0 or higher". You turn it on in the EdgeTX Internal/External RF Model Setup menu by setting Arm using to Switch github.com.

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Source: 4.0.0 release notes github.com. They give no channel table for other modes (Gemini, 16ch, hybrid); check the ExpressLRS docs for yours.

After updating, re-check radio mixes, the Betaflight Modes tab and failsafe with props off. Our EdgeTX model setup guide covers the arm switch, and our Betaflight failsafe guide covers the bench check.

New packet modes (LR1121)

Under "Expanded packet modes for LR1121", the 4.0.0 notes say "LR1121 gets more, up to a staggering 20 packet modes." New ones: K1000 2.4 (1000 Hz FSK, module baud rate 921k or higher), DK250 2.4, D50 LoRa 900 and 25 Hz LoRa 900. Team900, Team2.4 and GemX are now picked by band github.com.

The notes don't list these modes for SX1280 hardware. SPI receivers are limited to 50, 150, 250 and 500 Hz expresslrs.org. Our ELRS packet rate guide explains all of the modes.

Dynamic power, telemetry, web UI and Lua

• Dynamic power: fixed SNR thresholds are replaced by a statistical model "expected to result in 99%+ LQ" (link quality), mainly helping LR1121 systems github.com.
• Telemetry: Gemini mode doubles telemetry bandwidth; standard telemetry at 500 Hz gets about 30% more (14 Betaflight items in 5.1 s instead of 6.6 s) github.com.
• Web UI: new web UI, and "Linkstats are always sent to the handset, even when disconnected." github.com
• Lua: the script is now elrs.lua (r16). "Be sure to delete the existing elrsV3.lua and elrsV3.luac" so you don't get two ExpressLRS tools; "The newest elrs.lua works with all ExpressLRS versions back to 2.0." github.com

Settings wiped by the LittleFS change

The flash filesystem changed from SPIFFS to LittleFS, and "There is no way to upgrade the filesystem in place." github.com When you go from 3.x to 4.x:

The 4.0.0 notes add: "The hardware.json can be downloaded from the webui before updating and then replaced after updating." github.com

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What changed in 4.1

4.1.0 is "Compatible with all hardware running any ExpressLRS 4.x version". The main changes, all from the 4.1.0 notes github.com:

• Bind phrase from the handset: set it on a TX or receiver from a separate Lua tool linked in the notes.
• Dynamic power drops sooner: the power-down threshold went from +1.5 SD to +0.5 SD.
• Safer mode changes: the receiver refuses to switch to a mode it doesn't support.
• No zeros sent to the flight controller at startup: the receiver waits until all channels have been received at least once.
• Fewer "Telemetry Lost" callouts, thanks to a linearly scaled grace period.
• Web UI and telemetry additions: VBAT calibration, multiple voltage sensors, WiFi signal strength, GPS time sync and a HoTT airspeed sensor.
• LR2021 groundwork: "Full LR2021 support coming soon." Don't buy LR2021 hardware expecting full support in 4.1.0.

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Should you update? Decision box

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If you update: the safe order

Firmware warning: flashing the wrong target can leave a receiver or module unusable until you recover it. Use your device's exact target and read the official notes for your version: 4.0.0 and 4.1.0.

Overview only; full steps are in the ExpressLRS firmware update guide.

1. Back up everything on the checklist above.
2. Update the TX module (internal or external) to 4.1.0.
3. Update every receiver you plan to fly: UART receivers with ExpressLRS Configurator or WiFi, and SPI whoops by reflashing Betaflight 2026.6 with ELRSV4 (see how to update Betaflight).
4. On the radio, replace elrsV3.lua/elrsV3.luac with the new elrs.lua.
5. Rebind (bind phrase or bind button): see how to bind an ELRS receiver.
6. Props off: check the arm switch in the Betaflight Receiver and Modes tabs, then test failsafe (see Betaflight failsafe with ELRS).

Regulatory domain: the LittleFS change erases regulatory domain overrides github.com. Flash the firmware and domain that are legal where you fly, then confirm it on the Lua version line expresslrs.org. Don't run firmware for a different region.

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Staying on 3.x: what you need to know

• 3.x is still patched. 3.6.4 (Jun 8, 2026) fixed ESP8285 PWM jitter, the FM30 DC-DC converter, and output power on PDET radios such as the TX16S and Zorro github.com.
• The new elrs.lua still works on 3.x (see the Lua note above).
• Watch new gear. New radios and receivers may arrive on either major version. Check the Lua version line and the receiver's web UI before you assume they'll bind.

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FAQ

Is ELRS 4 compatible with ELRS 3?

No. The 4.0.0 release notes say 4.x is "Not compatible with ExpressLRS 3.x.x, 2.x.x, or 1.x.x."

Does my whoop's SPI receiver work with ELRS 4?

Only if it runs a Betaflight 2026.6 build with ELRSV4 set. Default builds are V3, per the Betaflight 2026.6 release notes. First check that your whoop really has an SPI receiver; some current whoops use a serial one.

Will updating erase my settings?

Going from 3.x to 4.x erases custom hardware.json and Options tab settings; PWM mappings and serial protocols stay (4.0.0 release notes).

Why did my arm switch stop working after updating?

Per the 4.0.0 release notes, in 8ch and 12ch Full Res modes the arm flag moved to CH14 and CH5 is now a full channel. Re-check mixes and the Modes tab, props off.

Can I downgrade back to 3.x?

The 4.0.0, 4.0.1 and 4.1.0 notes don't describe a downgrade path. Keep your backups; the TX and every receiver would have to go back together.

Which ExpressLRS Configurator version do I need?

Neither the ExpressLRS nor the Configurator release notes name a minimum for 4.x. Use the latest, 1.8.3 (Jul 22, 2026).

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Sources and versions checked (October 13, 2026): ExpressLRS releases 4.1.0, 4.0.1, 4.0.0, 3.6.4; ExpressLRS Configurator releases; ExpressLRS binding docs; ExpressLRS SPI receiver docs; ExpressLRS STM32 notice; Betaflight 2026.6 release notes; EdgeTX 2.6.0 backup notes; RadioMaster firmware page; RadioMaster Pocket page; BetaFPV Meteor75 Pro page. See how we research.

Next step: update your ELRS firmware → bind your receiver → choose a packet rate.