# Prusa Firmware Buddy changelog > Prusa Firmware Buddy release notes. - Vendor: Prusa - Category: Operating Systems - Official site: https://github.com/prusa3d/Prusa-Firmware-Buddy - Tracked by: What's New (https://whatsnew.fyi/product/prusa-firmware-buddy) - Harvested from: GitHub (prusa3d/Prusa-Firmware-Buddy) - Entries below: 10 (newest first) What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog. ## Releases ### v6.6.3 — 6.6.3 Firmware for Prusa CORE One+ INDX, CORE One INDX - Date: 2026-07-20 - Version: v6.6.3 - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.6.3 - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.6.3 - **changed** — Improved head LED behavior by synchronizing tool LEDs with the printer state and matching the status indication used by the heated bed LEDs - **added** — Add Nozzle Cleaner Y Offset adjustment to the Tune menu for easier calibration directly from the printer interface - **added** — Add ringdown decay information to the Sensor Info screen for improved diagnostics and troubleshooting - **changed** — Improved synchronization of loadcell samples between the toolhead and xBuddy, increasing the robustness of probing and calibration procedures - **changed** — Optimized motion step calculations to reduce the risk of layer shifts during printing - **changed** — Streamlined hotend management logic to improve maintainability and reliability - **changed** — Reduced calibration time by skipping temperature residency during tool offset calibration heating - **fixed** — Reworked nozzle heater self-test validation to use thermal model evaluation during heating, reducing false self-test failures caused by minor deviations in heating performance - **added** — Add validation of INDX coil current during heater self-tests to detect abnormal nozzle behavior - **changed** — Updated INDX nozzle thermal diagnostics to leverage thermal protection results for more accurate fault detection - **fixed** — Fixed an issue where hotend thermal errors could be reported even when no nozzle was installed by verifying nozzle presence before triggering errors - **fixed** — Fixed the Tool Change button incorrectly opening the extruded filament submenu - **fixed** — Fixed an issue where an uninitialized nozzle temperature was displayed as 15 °C in the footer ##### Summary * **Improvements** * Improved head LED behavior by synchronizing tool LEDs with the printer state and matching the status indication used by the heated bed LEDs. * Added Nozzle Cleaner Y Offset adjustment to the Tune menu for easier calibration directly from the printer interface. * Added ringdown decay information to the Sensor Info screen for improved diagnostics and troubleshooting. * Improved synchronization of loadcell samples between the toolhead and xBuddy, increasing the robustness of probing and calibration procedures. * Optimized motion step calculations to reduce the risk of layer shifts during printing. * Streamlined hotend management logic to improve maintainability and reliability. * Reduced calibration time by skipping temperature residency during tool offset calibration heating. * **Fixes** * Reworked nozzle heater self-test validation to use thermal model evaluation during heating, reducing false self-test failures caused by minor deviations in heating performance. * Added validation of INDX coil current during heater self-tests to detect abnormal nozzle behavior. * Updated INDX nozzle thermal diagnostics to leverage thermal protection results for more accurate fault detection. * Fixed an issue where hotend thermal errors could be reported even when no nozzle was installed by verifying nozzle presence before triggering errors. * Fixed the Tool Change button incorrectly opening the extruded filament submenu. * Fixed an issue where an uninitialized nozzle temperature was displayed as 15 °C in the footer. * Removed a redundant cooldown check from the nozzle cleaner calibration process. This is the **stable release of firmware** 6.6.3 for the Prusa CORE One+ INDX and CORE One INDX. ### v6.6.2 — 6.6.2 Firmware for Prusa CORE One+ INDX, CORE One INDX - Date: 2026-07-10 - Version: v6.6.2 - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.6.2 - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.6.2 - **changed** — Adjusted the nozzle cleaner origin position and fixed handling of nozzle cleaner offsets during parking moves - **changed** — EEPROM-stored nozzle cleaner offsets are now automatically adjusted after the update, eliminating the need for nozzle cleaner recalibration - **changed** — Adjusted the tool lock move distance for improved tool pickup reliability and reduced risk of filament being unintentionally ejected from the extruder gears - **added** — Added a new option in the Tune menu for fine-tuning the nozzle cleaner X offset - **fixed** — Fixed bumping into the waste bin after an MBL failure - **fixed** — Fixed an issue requiring tool removal during Dock Calibration even when no tool was loaded in the head - **fixed** — Fixed support for older xBuddy revisions with inverted pins (early MK4 converted boards) - **fixed** — Fixed selftest gray buttons not updating after dependencies were met - **fixed** — Fixed incorrect feedrate when loading PLA after FLEX material - **fixed** — Fixed an invisible Abort button on the Y-axis Input Shaper selftest screen - **fixed** — Fixed Tool Offset Cyphal communication not being reinitialized after board reset ##### Summary * **Improvements** * Adjusted the nozzle cleaner origin position and fixed handling of nozzle cleaner offsets during parking moves. * EEPROM-stored nozzle cleaner offsets are now automatically adjusted after the update, eliminating the need for nozzle cleaner recalibration. * Adjusted the tool lock move distance for improved tool pickup reliability and reduced risk of filament being unintentionally ejected from the extruder gears. * Added a new option in the **Tune** menu for fine-tuning the nozzle cleaner X offset. * **Fixes** * Fixed bumping into the waste bin after an MBL failure. * Fixed an issue requiring tool removal during Dock Calibration even when no tool was loaded in the head. * Fixed support for older xBuddy revisions with inverted pins (early MK4 converted boards). *(Credit: @ScottKolo)* * Fixed selftest gray buttons not updating after dependencies were met. * Fixed incorrect feedrate when loading PLA after FLEX material. * Fixed an invisible **Abort** button on the Y-axis Input Shaper selftest screen. * Fixed Tool Offset Cyphal communication not being reinitialized after board reset. This is the **stable release of firmware** 6.6.2 for the Prusa CORE One+ INDX and CORE One INDX. ### v6.6.1 — 6.6.1 Firmware for Prusa CORE One+ INDX, CORE One INDX - Date: 2026-07-02 - Version: v6.6.1 - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.6.1 - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.6.1 - **changed** — Lower the print bed when a tool is unknown or lost, allowing the user to safely remove the print - **changed** — During Dock Calibration, users can now choose between Keep, Calibrate, and Invalidate - **added** — Added an M109 flag to skip temperature stabilization - **fixed** — Fixed spontaneous INDX Head resets - **fixed** — Fixed incorrect tool assignment after a REDSCREEN reset by saving the currently selected tool - **removed** — Removed the extruder filament sensor from the footer and the Sensor Info menu ##### Summary - **Improvements** - Lower the print bed when a tool is unknown or lost, allowing the user to safely remove the print. - During Dock Calibration, users can now choose between **Keep**, **Calibrate**, and **Invalidate**. - Added an `M109` flag to skip temperature stabilization. - **Fixes** - Fixed spontaneous INDX Head resets. - Fixed incorrect tool assignment after a REDSCREEN reset. The printer now saves the currently selected tool. - Removed the extruder filament sensor from the footer and the Sensor Info menu. This is the **stable release of firmware** 6.6.1 for the Prusa CORE One+ INDX, CORE One INDX. ### v6.6.0 — 6.6.0 Firmware for Prusa CORE One+ INDX, CORE One INDX - Date: 2026-06-25 - Version: v6.6.0 - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.6.0 - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.6.0 - **added** — First firmware release for the Prusa CORE One/+ INDX - **added** — Full INDX toolchanger support with automatic tool changes for up to 8 tools - **added** — Contactless nozzle induction heating with temperature compensation accounting for extrusion speed, chamber temperature, print fan speed, and filament thermal properties - **added** — Continuous nozzle presence detection that verifies the picked-up tool's nozzle is present approximately every 100 ms while idle and every 500 ms while heating - **added** — Contactless tool offset sensor mounted on the print bed to automatically measure each tool's XY offset with thermal compensation - **added** — Guided INDX calibrations including homing, dock, tool offset, nozzle cleaner, Input Shaper, and Phase Stepping calibration - **added** — Automatic, low-waste nozzle cleaning with integrated nozzle cleaner and wastebin - **added** — Screen for unloading or changing all filaments at once - **added** — Side filament sensor for every tool slot to detect filament runout on a per-tool basis - **added** — Empty Nozzle Cleaner function to easily empty the wastebin with automatic pause capability for prints with high number of tool changes - **changed** — Reworked tool mapping screen supporting up to 8 tools - **changed** — Homing calibration reworked for the INDX toolhead with improved accuracy and repeatability, automatic detection and retry of invalid probes, and redesigned calibration pattern - **changed** — Filament change screen now offers Set all to feature to assign a filament type to all slots at once - **changed** — Unload all feature added to clear the printer in a single operation, working even when loaded filament type is unknown ##### Summary **New features and improvements** - First firmware release for the Prusa CORE One/+ INDX - Full INDX toolchanger support, with automatic tool changes for up to 8 tools - Contactless nozzle induction heating - Continuous nozzle presence detection for safety and fault detection - Contactless tool offset sensor - Guided INDX calibrations: docks, tool offsets, nozzle cleaner, and more - Automatic, low-waste nozzle cleaning with a wastebin - Screen for unloading or changing all filaments at once - Reworked tool mapping screen supporting up to 8 tools - Empty Nozzle Cleaner - **Known issues are listed at the end** This is the **first firmware release for printers equipped with the INDX toolchanger,** and it builds on the current firmware. It adds complete support for the INDX hardware, including automatic tool changes with up to 8 tools, induction heating, and a guided calibration workflow that takes you from assembly to your first multi-material print. #### Welcome, INDX! The **INDX toolchanger**, developed by **Bondtech** in collaboration with **Prusa Research**, transforms your CORE One/+ into a multi-material printer with up to 8 tools. The system combines a single active **INDX Head** with lightweight **passive tools**. Each tool consists of a filament path and a nozzle, with no heaters, wires, or electronics. After installing the conversion kit and flashing this firmware, the printer identifies itself as a CORE One+ INDX and guides you through the initial calibrations. Both the **4-tool and 8-tool** kit configurations are supported. The firmware lets you calibrate and enable any number of tools from 1 to 8, so you can run the printer with exactly as many tools as your print requires. ##### Induction heating with temperature compensation The INDX Head heats the nozzle of the currently picked-up tool by induction and measures its temperature contactlessly. In addition, the firmware runs a thermal compensation model that accounts for extrusion speed, chamber temperature, print fan speed, and the thermal properties of the loaded filament, keeping the actual melt temperature on target across changing print conditions. The INDX Head also independently monitors its own temperatures, adding an extra layer of safety on top of the printer's standard thermal protections. Because the nozzles heat up in seconds, the time required for temperature stabilization is significantly shorter than on a conventional hotend. ##### New contactless tool offset sensor The new inductive sensor mounted on the print bed automatically measures each tool's XY offset, ensuring that every tool prints in perfect alignment. The tools are heated during the measurement process, compensating for slight changes in the thermal expansion of the metal nozzle. ##### Continuous nozzle presence detection For safe and reliable multi-tool printing, the INDX Head continuously verifies that the picked-up tool's nozzle is present. It detects the nozzle through its induction system and re-checks it approximately every 100 ms while idle and every 500 ms while heating. If a nozzle goes missing - whether because a tool has fallen off its dock or a pick or park operation did not complete successfully - the printer detects the issue and responds safely instead of heating or extruding without a nozzle in place. Ambiguous readings, such as a nozzle caught halfway, are treated cautiously and resolved by the system's recovery logic. ##### Guided INDX calibrations The Calibrations & Tests wizard has been extended with new INDX-specific routines and guides you through the complete setup process in the correct order: - **Homing calibration**: Reworked for the INDX toolhead with improved accuracy and repeatability. Invalid probes are detected and retried automatically, and the calibration pattern has been redesigned, which is essential for repeatable tool docking. - **Dock calibration**: Fine-tunes the position of each dock t _[Truncated at 4000 characters — full notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.6.0]_ ### v6.5.7 — 6.5.7 Firmware for Prusa CORE One L, CORE One+, CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S, MK3.5 - Date: 2026-06-18 - Version: v6.5.7 - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.5.7 - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.5.7 - **changed** — Improved filament change procedure to better handle switching between materials with significantly different print temperatures by preheating to the higher temperature and then adjusting to match the newly inserted material - **fixed** — Support for older xBuddy board versions - **fixed** — Input shaper calibration for CoreXY printers now correctly uses XY coordinates instead of AB coordinates - **fixed** — Fixed not loading custom Connect certificates when using Load Settings from File menu item - **fixed** — Fixed a crash when printing G-Code files with more than 1024 objects ##### Summary - **New features and improvements** - Improved filament change between different materials - **Fixes** - Support for older xBuddy board versions - Fixed input shaper calibration for CoreXY printers - Fixed not loading custom Connect certificates - Fixed a crash when printing more than 1024 objects This is the **stable release of firmware 6.5.7** for the Prusa CORE One L, CORE One+, CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S and MK3.5 bringing targeted stability improvements and fixes. ##### Improved filament change between different materials The filament change procedure has been improved to better handle switching between materials with significantly different print temperatures. When loading the new filament, the printer now preheats to the higher temperature of the two materials. Once the filament is in the nozzle, the target temperature is adjusted to match the newly inserted material. This allows the nozzle to cool down gradually when switching to a lower-temperature material, while the previous filament is purged out. ##### Fixed input shaper calibration for CoreXY printers Input shaper calibration on CoreXY printers now correctly uses XY coordinates instead of AB coordinates. This fixes an incorrect excitation pattern that could lead to inaccurate calibration results. ##### Fixed not loading custom Connect certificates Our customers can set up their printers to use non-official Connect servers by using the “Load Settings from File” menu item. This should also include loading a custom SSL certificate, which was however not working due to a bug in the firmware that has now been fixed. _Please note that we do not open-source our Connect backend infrastructure._ ##### Fixed a crash when printing more than 1024 objects We addressed a crash triggered when trying to print a G-Code file with more than 1024 objects. ### v6.4.2 — 6.4.2 Firmware for Prusa XL & MINI - Date: 2026-06-03 - Version: v6.4.2 - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.4.2 - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.4.2 - **fixed** — Custom Connect certificates are now loaded correctly when using the "Load Settings from File" menu item ##### Summary - **Fixes** - Fixed not loading custom Connect certificates This is the **stable release of firmware 6.4.2** for the Prusa XL, MINI. ##### Fixed not loading custom Connect certificates Our customers can set up their printers to use non-official Connect servers by using the “Load Settings from File” menu item. This should also include loading a custom SSL certificate, which was however not working due to a bug in the firmware that has now been fixed. _Please note that we do not open-source our Connect backend infrastructure._ ### v6.4.1 — 6.4.1 Firmware for Prusa XL - Date: 2026-04-20 - Version: v6.4.1 - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.4.1 - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.4.1 - **changed** — Improve phase stepping calibration by refining the calibration method and backporting fixes from 6.5 releases - **fixed** — Fix homing issues with no tool picked that could cause motor skipping or put the printer into an invalid state - **fixed** — Fix toolchanger service moves being affected by user feedrate override by ensuring tool parking, picking, and alignment moves run at intended speeds - **changed** — Relax nozzle cleaning checks to prevent false nozzle cleaning failed errors - **changed** — Relax print fan selftest thresholds to reduce false failures due to fan-to-fan variation across different fan shroud revisions ##### Summary - Improved phase stepping calibration - Fixed homing issues with no tool picked - Fixed toolchanger service moves being affected by user feedrate override - Relaxed nozzle cleaning checks to prevent false nozzle cleaning failed errors - Relaxed print fan selftest thresholds to reduce false failures - **Known issue** - _Power panic resulting in a BSOD_ This is the **stable release** of firmware **6.4.1 for the Prusa XL** bringing targeted stability improvements and fixes - most notably addressing several homing and toolchanging reliability issues. ##### Improved phase stepping calibration The switch to the new universal phase stepping calibration in the 6.4 release caused a regression in the calibration quality for some XL users. In 6.4.1, the calibration method has been refined and further improved by backporting phase stepping fixes from the 6.5 releases. These changes enhance overall calibration reliability and address regressions introduced in earlier 6.4 builds. ##### Fixed homing issues with no tool picked Homing without a tool picked could cause audible motor skipping or put the printer into an invalid state under certain conditions. The fix ensures that the axes are properly homed before attempting a tool pick, preventing both issues. ##### Fixed toolchanger service moves being affected by user feedrate Tool parking, picking, and alignment moves could be slowed down if a low feedrate was set in G-code beforehand. This could lead to unreliable tool changes. All toolchanger service moves now run at their intended speeds regardless of the user feedrate setting. ##### Relaxed print fan selftest thresholds to reduce false failures The print fan selftest could incorrectly report a failure on some units due to tight RPM thresholds that did not account for normal fan-to-fan variation across different fan shroud revisions. The thresholds have been relaxed to reduce false failures. ### v6.4.1-RC — 6.4.1-RC Firmware for Prusa XL - Date: 2026-03-30 - Version: v6.4.1-RC - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.4.1-RC - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.4.1-rc - Labels: Pre-release - **fixed** — Backport phase stepping fixes from 6.5 releases to improve phase stepping and prevent regressions ##### Summary - **Fixes** - Phase stepping fixes from the 6.5 releases This is the **release candidate** for the upcoming **firmware 6.4.1** for the **Original Prusa XL**. For a complete overview of features introduced in firmware 6.4.1, users can refer to the [6.4.1-beta](https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.4.1-beta) published earlier. ##### Phase stepping fixes from the 6.5 releases Phase stepping fixes from 6.5 have been backported to 6.4.1. This improves phase stepping and prevents regressions introduced in earlier 6.4 builds. ### v6.5.3 — 6.5.3 Firmware for Prusa CORE One L, CORE One+, CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S, MK3.5 - Date: 2026-03-24 - Version: v6.5.3 - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.5.3 - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.5.3 - **changed** — Massively speed up MMU filament changes by up to 9 seconds through parallelized unloading and idler engaging, optimized idler selection, and improved FeedingToFinda phase - **changed** — Updated default input shaper profiles for C1+ and C1L - **changed** — Updated translations - **added** — Bed LED progress indicator on C1L showing print progress from left side with color change from white to blue - **changed** — Tuned parking position during purging on C1, C1+, and C1L to reduce potential debris on print bed - **added** — Vent grille now automatically opens or closes based on target chamber temperature set in active filament preset on C1+ and C1L - **changed** — Increased maximum supported AC supply voltage for the AC controller to 264 V on C1L - **added** — Preload all MMU slots at once with single filament type selection - **changed** — Updated bootloader to version 2.6.0 - **changed** — Lowered chamber safety temperatures on C1 with fans starting at 60 °C and overheating warning pause at 65 °C - **fixed** — Fixed input shaper X and Y axis assignment on CoreXY printers which were previously swapped - **fixed** — Fixed layer shifts during high-speed curved moves - **fixed** — Fixed M1704 MMU load test gcode to consider toolmapping - **fixed** — Fixed MMU sending spurious attention reports to Prusa Connect during normal toolchanges - **fixed** — Fixed crash or BSOD on M501 restore settings command - **fixed** — Fixed gearbox alignment test showing wrong status when skipped - **fixed** — Fixed chamber fans showing Auto instead of Disabled when not in use on C1, C1+, and C1L ##### Summary - **New features and improvements** - Massively speed up MMU filament changes [MMU] - Updated default input shaper profiles [C1+, C1L] - Updated translations (beta didn’t have new texts translated) - Bed LED progress indicator [C1L] - Tuned parking position during purging [C1, C1+, C1L] - Vent grille linked to filament preset [C1+, C1L] - AC supply voltage for the AC controller has been increased [C1L] - Preload all MMU slots at once [MMU] - Bootloader update - Lowered chamber safety temperatures [C1] - **Fixes** - Fixed input shaper axis assignment on CoreXY printers - Fixed layer shifts during high-speed curved moves - M1704 MMU load test gcode now considers toolmapping [MMU] - Fixed MMU sending spurious attention reports to Prusa Connect during normal toolchanges [MMU] - Fixed crash/BSOD on M501 (restore settings) ([#4912](https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/4912)) - Fixed gearbox alignment test showing wrong status when skipped - Fixed chamber fans showing "Auto" instead of "Disabled" when not in use [C1, C1+, C1L] This is the stable release of firmware 6.5.3 for the Prusa CORE One L, CORE One+, CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S and MK3.5 bringing targeted stability improvements and fixes. ##### Massively speed up MMU filament changes [MMU] A series of improvements have been implemented that massively speed up MMU filament changes **by up to 9 seconds**. Some changes in the MMU firmware were required as well, so **it is necessary to flash a [new 3.0.4 firmware](https://www.google.com/url?q=https://github.com/prusa3d/Prusa-Firmware-MMU/releases/tag/v3.0.4&sa=D&source=docs&ust=1773131390056718&usg=AOvVaw1-toj-3WO51cdOwPWjwVdX) to your MMU unit**. The improvements include: - Parallelized unloading filament from the nozzle and idler engaging. - The printer does not wait for the final idler disengagement to finish to continue printing. - Parallelized selector and idler movement. - FeedingToFinda phase now obeys PulleySlowFeedrate with higher value. - Optimized idler selection mechanism during filament change. _For more information about MMU improvements and the CORE One L MMU3, [check out our blog post.](https://blog.prusa3d.com/massive-mmu3-speed-boost-new-fw-slashes-filament-change-times-core-one-l-mmu3-news_132957/)_ ##### Updated default input shaper profiles [C1+, C1L] In 6.5.3-beta, we’ve fixed a bug in the input shaper configuration of our CoreXY printers. **If you haven’t changed your input shaper settings, the new values will update automatically.** NOTE: If you have **CORE One L** or an **accelerometer accessory**, we recommend re-running your input shaper calibration. If you modified these values in the past **we recommend resetting your input shaper profiles to defaults** using the _Settings → Input Shaper → Restore Defaults_. ##### Bed LED progress indicator [C1L] The CORE One L bed LED indicator now shows the progress of your print, starting from the left and gradually changing from white to blue. ##### Tuned parking position during purging [C1, C1+, C1L] The parking position on CORE One and CORE One L has been adjusted so that purged filament flows unobstructed to the bottom, reducing potential debris on the print bed. ##### Vent grille linked to filament preset [C1+, C1L] The vent grille now automatically opens or closes based on the target chamber temperature set in the active filament preset. This ensures optimal thermal conditions during printing. ##### AC supply voltage for the AC controller has been increased [C1L] Based on user feedback, we have increased the maximum supported AC supply voltage for the AC controller to 264 V. ##### Preload all MMU slots at once [MMU] The new menu item _Filament MMU - Preload All_ now asks for the filament type only once and applies it to all slots. This is handy when you want to load, for example, five PLA filaments. #### _[Truncated at 4000 characters — full notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.5.3]_ ### v6.5.3-RC — 6.5.3-RC Firmware for Prusa CORE One L, CORE One+, CORE One, MK4S, MK4, MK3.9S, MK3.9 - Date: 2026-03-16 - Version: v6.5.3-RC - Original notes: https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.5.3-RC - Permalink: https://whatsnew.fyi/product/prusa-firmware-buddy/releases/v6.5.3-rc - Labels: Pre-release - **changed** — Massively speed up MMU filament changes by up to 9 seconds through parallelized unloading and movement optimization - **changed** — Update default input shaper profiles for CORE One+ and CORE One L - **changed** — Update translations - **fixed** — M1704 MMU load test gcode now considers toolmapping - **fixed** — Fix MMU sending spurious attention reports to Prusa Connect during normal toolchanges ##### Summary - **New features and improvements** - Massively speed up MMU filament changes [MMU] - Updated default input shaper profiles [C1+, C1L] - Updated translations (beta didn’t have new texts translated) - **Fixes** - M1704 MMU load test gcode now considers toolmapping [MMU] - Fixed MMU sending spurious attention reports to Prusa Connect during normal toolchanges [MMU] This is the **release candidate** for the upcoming firmware **6.5.3 for the Prusa CORE One L, CORE One+, CORE One, MK4S, MK4, MK3.9S and MK3.9.** For a complete overview of features introduced in **firmware 6.5.3**, users can refer to the [6.5.3-beta](https://github.com/prusa3d/Prusa-Firmware-Buddy/releases/tag/v6.5.3-beta) published earlier. ##### Massively speed up MMU filament changes [MMU] A series of improvements have been implemented that massively speed up MMU filament changes **by up to 9 seconds**. Some changes in the MMU firmware were required as well, so **it is necessary to flash a [new 3.0.4 firmware](https://www.google.com/url?q=https://github.com/prusa3d/Prusa-Firmware-MMU/releases/tag/v3.0.4&sa=D&source=docs&ust=1773131390056718&usg=AOvVaw1-toj-3WO51cdOwPWjwVdX) to your MMU unit**. The improvements include: - Parallelized unloading filament from the nozzle and idler engaging. - The printer does not wait for the final idler disengagement to finish to continue printing. - Parallelized selector and idler movement. - FeedingToFinda phase now obeys PulleySlowFeedrate with higher value. - Optimized idler selection mechanism during filament change. ##### Updated default input shaper profiles [C1+, C1L] In 6.5.3-beta, we’ve fixed a bug in the input shaper configuration of our CoreXY printers. **If you haven’t changed your input shaper settings, the new values will update automatically.** NOTE: If you have **CORE One L** or an **accelerometer accessory**, we recommend re-running your input shaper calibration. If you modified these values in the past **we recommend resetting your input shaper profiles to defaults** using the _Settings → Input Shaper → Restore Defaults_.