ExpressLRS 4.0: Everything New in the World’s Fastest RC Link
ExpressLRS has become the de facto standard radio control link for FPV drones, and version 4.0 raises the bar yet again. Building on the LoRa-based foundation that delivered 500Hz update rates and sub-millisecond latency, ELRS 4.0 introduces dual-band simultaneous transmission, adaptive data rate negotiation, and the most significant receiver hardware evolution since the platform launched. Here is everything you need to know.
Dual-Band Gemini: 2.4GHz and 900MHz Simultaneously
The flagship feature of ELRS 4.0 is Gemini — true dual-band simultaneous transmission. Unlike the previous “dual-band” implementations that switched between 2.4GHz and 900MHz based on link quality (diversity switching), Gemini transmits the same control data on both bands simultaneously. The receiver combines both signals, achieving massive link budget improvement in challenging RF environments.
In practical terms, this means flying behind solid obstacles — buildings, terrain features, dense forest canopy — with dramatically reduced risk of failsafe. The 2.4GHz link provides low-latency primary control while the 900MHz link acts as a robust fallback that penetrates where 2.4GHz cannot. Testing at abandoned industrial sites showed reliable control at ranges and obstacle densities that would failsafe any single-band system.
Gemini requires specific hardware: the Radiomaster Gemini module (dual-band transmitter) and the matching Gemini receiver (dual-band receiver with two antennas — one for each band). It is backward compatible — you can still bind to standard single-band receivers at full 4.0 feature parity, just without the dual-band link robustness.
FLRC Mode: Pushing the Latency Frontier
ELRS 4.0 introduces FLRC (Fast LoRa with Reduced Coding), an experimental ultra-low-latency mode that cuts packet transmission time by nearly 40% compared to standard LoRa 500Hz. FLRC achieves end-to-end latency (stick movement to servo/ESC response) of approximately 1.8ms — a number that approaches the physical limits of the RC control chain.
The trade-off is range. FLRC mode sacrifices coding gain and spreads the signal across a narrower bandwidth, resulting in approximately 60-70% of standard mode’s effective range. For racing within 200-300 meters — the vast majority of competitive FPV — this is an excellent trade. For long-range mountain surfing, standard 250Hz or 150Hz modes remain the correct choice.
FLRC requires compatible receiver hardware with the newer SX1280 chipset revision. Most receivers manufactured from mid-2025 onward (Radiomaster RP1 V2, Happymodel EP1 V3, BetaFPV SuperD) support FLRC natively with a firmware update.
Adaptive Data Rate: Dynamic Mode Switching
Previous ELRS versions locked you into a single packet rate for the entire flight. ELRS 4.0 introduces adaptive data rate (ADR), which dynamically shifts between 500Hz, 250Hz, 150Hz, and 50Hz depending on link quality. Fly close with clean RSSI, and the link stays at 500Hz for maximum responsiveness. Push into RF-hostile terrain, and the link automatically downshifts through the rates — trading a few milliseconds of latency for dramatically more robust link budget.
The transitions are seamless. In field testing, pilots reported noticing the transition only through the OSD element showing current packet rate — not through any change in control feel. This is because the downshift only occurs after repeated packet loss, and the upshift happens only after sustained clean signal, preventing oscillation between modes.
Receiver Hardware Evolution
The Radiomaster RP1 V2 is the definitive 4.0 receiver. It adds a second amplifier stage for improved sensitivity at low signal levels, a TCXO for rock-solid frequency stability from -20°C to +85°C, and the updated SX1280 variant required for FLRC mode. At 1.2g including antenna, it disappears into any build.
For AIO builds, the Happymodel EP2 V3 squeezes full ELRS 4.0 compatibility (including FLRC) onto a ceramic-tower antenna design at 0.42g. The integrated antenna limits range to 500-800m but saves weight and eliminates fragile external antennas — ideal for 1S whoops and ultralight toothpick builds.
Gemini receivers are heavier (3.5g for the Radiomaster RP1 Gemini) due to the dual RF path but represent the ultimate in link reliability. For freestyle pilots pushing through bandos and industrial sites, the weight penalty is invisible on a 5-inch build and the link security is transformative.
Migrating to 4.0
ELRS 4.0 is not backward compatible with 3.x. You must flash both your transmitter module and all receivers to 4.0 firmware. The ExpressLRS Configurator handles this smoothly with the unified target system — select your hardware, choose 4.0.0, and flash via USB or WiFi (for ESP-based receivers).
After flashing, rebind all receivers. The binding phrase system carries over — if you use the same binding phrase on your 3.x configuration, the 4.0 firmware will maintain the same derived UID and your receivers will bind without manual intervention. Verify the bind before flight; some early-production receivers require a manual bind phrase re-entry after the first 4.0 flash.
The configuration has been streamlined. The Lua script on your radio now presents a simplified settings page with preset “Performance” (500Hz FLRC), “Balanced” (250Hz standard, ADR enabled), and “Long Range” (50Hz) profiles. Most pilots will set-and-forget the Balanced profile and never touch settings again.
ExpressLRS 4.0 does not fundamentally change what ELRS is — it refines it. The link feels the same, just more reliable in more places. For FPV pilots who have ever experienced a failsafe at an inconvenient moment, the dual-band Gemini hardware alone justifies the upgrade.