6.4.1 Firmware for Prusa XL

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.

6.4.1-RC Firmware for Prusa XL

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 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.

6.5.3 Firmware for Prusa CORE One L, CORE One+, CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S, MK3.5

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)
  • 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 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.

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.

Bootloader update

The bootloader has been updated to version 2.6.0. This creates the necessary foundation for the upcoming INDX upgrade.

Lowered chamber safety temperatures [C1]

Chamber fans now start to spin at 60 °C and the printer shows a "chamber overheating" warning, pausing the print at 65 °C.

Please note that the maximum chamber target temperature is unchanged at 55 °C, only safety margins for emergency cooling have been adjusted.

Fixed input shaper axis assignment on CoreXY printers

The input shaper X and Y axis parameters were swapped on CoreXY printers, meaning the shaper configured for X was actually applied to Y, and vice versa. This also prevented users from disabling input shaping on only one axis. Both issues are now resolved.

Fixed layer shifts during high-speed curved moves

Layer shifts could occur during high-speed printing with curved moves. The motion system has been improved to address the issue.

Note: Please be aware that not all layer shifts have been caused by this issue.

6.5.3-RC Firmware for Prusa CORE One L, CORE One+, CORE One, MK4S, MK4, MK3.9S, MK3.9

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 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 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.

6.5.3-beta Firmware for Prusa CORE One L, CORE One +, CORE One, MK4S, MK4, MK3.9S, MK3.9

Summary

• New features and improvements
  • Bed LED progress indicator [C1L]
  • Tuned parking position during purging [C1, C1+, C1L]
  • Vent grille linked to filament preset [C1+, C1L]
  • Preload all MMU slots at once [MMU]
  • Bootloader update
• Fixes
  • Fixed input shaper axis assignment on CoreXY printers
  • Fixed layer shifts during high-speed curved moves
  • Fixed crash/BSOD on M501 (restore settings) (#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 beta release introduces firmware 6.5.3 for the Prusa CORE One L, CORE One, MK4S, MK4, MK3.9S and MK3.9.

For MK4S, MK4, MK3.9S and MK3.9, this is the first 6.5.x release, meaning all features and improvements from firmware 6.5.0, 6.5.1, and 6.5.2 are also included.

MMU3 owners please note: you need to upgrade the firmware in your MMU3 unit to version 3.0.4 (download link).

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.

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.

Bootloader update

The bootloader has been updated to version 2.6.0. This creates the necessary foundation for the upcoming INDX upgrade.

Fixed input shaper axis assignment on CoreXY printers

The input shaper X and Y axis parameters were swapped on CoreXY printers, meaning the shaper configured for X was actually applied to Y, and vice versa. This also prevented users from disabling input shaping on only one axis. Both issues are now resolved.

Fixed layer shifts during high-speed curved moves

Layer shifts could occur during high-speed printing with curved moves. The motion system has been improved to address the issue.

Note: Please be aware that not all layer shifts have been caused by this issue.

6.4.1-beta Firmware for Prusa XL

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 beta 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. The calibration method has been tuned to mitigate these issues.

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.

6.5.2 Firmware for Prusa CORE One L

Summary

• Fixed nozzle cleaning failed
• Improved PSU fan checks
• Improved AC Bed sensitivity to voltage fluctuations

This is the stable release of firmware 6.5.2 for the CORE One L, addressing several improvements and bug fixes, most notably false positive "Nozzle cleaning failed" errors.

Fixed nozzle cleaning failed

Both user feedback and our internal testing indicated that the nozzle cleaning checks were too strict, leading to false "Nozzle cleaning failed" errors. In some cases, the error appeared even with a brand new or freshly cleaned nozzle. We've tuned the detection parameters to reduce false positives while maintaining reliable contamination detection.

Improved PSU fan checks

We’ve adjusted the PSU fan checking parameters to prevent false PSU fan check failures.

Improved AC Bed sensitivity to voltage fluctuations

We made the AC bed less sensitive to mains voltage fluctuations. The printer should now handle small brownouts more reliably.

6.4.0 Firmware for Prusa CORE One +, CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S, MK3.5, MINI & XL

Update

Based on your feedback and the reports we’ve received, we’ve decided to withdraw firmware version 6.4.0 for the Original Prusa XL. The main issues are related to Phase Stepping calibration.
We are currently working on a fix, which should be available in the coming weeks.

If you are experiencing Phase Stepping issues (noise), layer shifts, or random tool crashes, please downgrade to the latest stable firmware version 6.2.6.

These issues affect only the Original Prusa XL. If you’re running firmware 6.4.0 on your MK4 or CORE One, there is no need to downgrade.

Summary

• New features

  • Automatic chamber vent opening/closing (C1/+)
  • Belt tuning wizard (C1/+)
  • Faster and more responsive Prusa Connect experience
  • Nozzle cleaning failed wizard
  • Auto-retract (MK4 family, XL)
  • Auto-retract improvements (C1/+)
  • Auto-retract disable option (C1/+)
  • Selective factory reset
  • Chamber support for backwards G-Code compatibility (C1/+)

• Changes and improvements

  • Improved print status messages
  • Lazier homing, more cautious calibration
  • Autoload improvements
  • Unified XL & CORE One chamber filtration
  • Option to continue after nozzle cleaning failure
  • Print sheet detection (MK4 family)
  • Respect maximum printed Z position
  • Gearbox alignment calibration (XL)
  • Filament change from Tune menu in any tool (XL)
  • Support cancelling more objects
  • Wi-Fi signal strength indicator
  • BSOD knob press behavior
  • Reworked filament sensor evaluation
  • Ukrainian language support for all printers

• Fixes

  • All the fixes from the 6.3.X releases have been expanded to other printers.
  • Various fixes and stability improvements

This is the stable release of firmware 6.4.0 for the CORE One+, CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S, MK3.5, MINI, and XL. It reunifies the firmware development branch after the temporary split during the CORE One launch, where 6.3.x was released exclusively for CORE One and other printers remained on 6.2.x. – along with bringing new features, quality-of-life improvements, and fixes across all platforms.

Automatic chamber vent opening/closing (C1/+)

The automatic chamber vent mechanism introduced with the CORE One L is now also available on the CORE One. After updating, the feature can be enabled via Settings → Hardware → Chamber Vent Control by selecting the Auto option.

A Manual mode is also available, which keeps the vents closed by default and only shows an informational reminder before each print.

Vents can be controlled manually using the new M870 G-code ("M870 O" = open, "M870 C" = close), although we do not recommend including these commands in slicer profiles, as the printer handles vent control automatically.

The printed parts required to retrofit this feature on existing CORE One printers will be published on Printables in the coming days. A link will be added here once available.

Belt tuning wizard (C1/+)

A new guided wizard has been added to the Prusa CORE One to help users properly tension the X/Y belts. The printer uses controlled belt excitation combined with stroboscopic feedback to visualize belt resonance, making the tuning process more intuitive and reliable.

The wizard, accessible via Settings → Manual Belt Tuning, begins by prompting the user to check that the gantry is properly aligned, as misalignment can affect measurement accuracy. A quick manual alignment can be done by loosening both tensioner bolts, gently straightening the gantry by hand, and re-tightening the bolts evenly while keeping the gantry square. More information about gantry alignment can be found in this article.

The wizard then measures the vibration frequency of both belts and recommends whether to tighten or loosen them. The target frequencies are 96 Hz for the upper belt and 92 Hz for the lower belt.
Important: Always tighten both tensioner bolts evenly and alternately. This ensures that the gantry stays square during adjustment.

NOTE: A difference of up to 8 Hz between the belts is acceptable, as long as both values remain within the 90–98 Hz range. If values cannot be reached, the wizard will suggest manual squaring before continuing.
If your gantry is out of alignment, you may not be able to reach these exact values. In some cases, the lower belt can even show a slightly higher frequency than the upper belt.

Faster and more responsive Prusa Connect experience

Communication between the printer and Prusa Connect is now handled using WebSockets, replacing the previous polling-based method.
While this change does not affect raw data transfer speed, it significantly improves overall responsiveness and interaction with the cloud service. Users can expect (via Prusa Connect):

• Lower latency when starting prints
• Faster execution of remote commands
• Smoother and more fluid control during cloud-based workflows

This update also lays the groundwork for future enhancements to remote monitoring and control by the user, allowing for continued improvements to the connected experience in future releases.

Nozzle cleaning failed wizard

The recovery process for failed nozzle cleaning has been reworked into a new step-by-step wizard.

The wizard also includes a filament retraction step to prevent oozing before retrying the automatic cleaning sequence, increasing the chance of successful recovery.

Auto-retract (MK4 family, XL)

The auto-retract feature is now enabled on MK4 and XL printers, after its first introduction on CORE One in firmware 6.3.X. Filament is automatically retracted from the nozzle at the end of each print, which helps reduce oozing during bed leveling and removes the need to preheat the nozzle when unloading.

NOTE: Auto-retraction is not applied to flexible filaments; to handle these, we have added a new “Is flexible” parameter, configurable in filament presets via the printer’s GUI or using the M865 G-code.

Auto-retract improvements

The auto-retract system has been improved across the board, with particularly noticeable benefits for multi-tool prints on the XL. It now respects slicer-issued retractions and avoids adding redundant movements.

On the MK4, the print head now parks at a higher Z-height after print completion to make it easier to remove any ooze left by the auto-retract ramming process.

Auto-retract disable option

Auto-retract can now be disabled globally in the Settings menu, although this is not recommended for standard use.

It is also possible to disable auto-retract per filament type. In the filament detail menu, the former "Flexible" option has been renamed to "Auto Retract", with its behavior adjusted accordingly.

Selective factory reset

We have introduced more granular control over the factory reset process. Instead of wiping all data at once, settings are now divided into categories, allowing you to decide what to reset and what to keep. These categories include:

• Calibrations: All the calibrations data and selftest results
• Common misconfigurations: Quirky settings that might cause unexpected behavior if you don’t know about them, for example disabling filament sensors, changing steps per mm
• Network: Wi-Fi, Ethernet, Prusa Connect, PrusaLink related items
• User interface: Items that affect user interaction with the printer – language, sound settings, footer settings, touchscreen, LEDs, and so on
• Stats: Print & error statistics
• HW configuration: Items that are linked to the hardware installed on the printer: nozzle diameters, extruder type, (also) steps per mm, printer type,...
• Printer functions: Configuration of various print functions, such as MMU, chamber filtration, HW checks,...
• User profiles: Custom filaments, print sheets (MINI and MK3.5)

To simplify the process, we have also prepared several reset presets for the most common scenarios:

• Ownership transfer: Useful when you’re giving the printer to someone else. Will reset all your personal settings such like network and filament profiles, but keep things like hardware configuration, calibrations and statistics.
• Fix common misconfigurations: This is what the support team will likely advise you to do during troubleshooting. Intended to fix things like filament sensor not working because it was accidentally turned off from the menu.
• Keep HW config: Keeps only the hardware configuration (what nozzles, fans, extruders the printer has), nothing else. This reset is performed before shipping assembled units to the customers.
• Full reset: Wipes everything, except for the firmware itself
• Hard reset: Wipes everything, including the firmware. A USB drive with a new firmware will be needed.

If none of the presets fits your needs, you can start with the closest one and then...

6.4.0-RC2 Firmware for Prusa CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S, MK3.5, MINI & XL

Summary

• New features

  • Automatic chamber vent opening/closing [C1]
  • Auto-retract improvements
  • Auto-retract disable option

• Fixes

  • Fixed XL toolcrashes [XL]
  • Fixed nozzle heating for unload when auto-retracted
  • Fixed XL enclosure not reporting temperature (#4800, #4829) [XL]
  • Fixed sensor info showing only zeroes (#4808)
  • Fixed stack overflow when downloading from Prusa Connect and opening Prusa Link at the same time
  • Fixed getting stuck in tool mapping after homing calibration gets recommended (#4799)
  • Fixed BSOD on M501 (#4912)
  • Fixed absorbing heat status showing wrong value (#4754)
  • Fixed BSOD when opening the door during nozzle cleaning [C1]

• Known issues [XL, MK4S, MK4, MK3.9S, MK3.9]

This is the second release candidate for the upcoming firmware 6.4.0 for the Prusa CORE One, MK4S, MK4, MK3.9S, MK3.9, MK3.5S, MK3.5, MINI & XL. It reunifies the firmware development branch after the temporary split during the CORE One launch, where 6.3.x was released exclusively for CORE One and other printers remained on 6.2.x – along with bringing new features, improvements, and fixes across all platforms.

For a complete overview of features introduced in firmware 6.4.0, users can refer to the 6.4.0-alpha release notes and 6.4.0-RC release notes published earlier.

Automatic chamber vent opening/closing [C1]

The automatic chamber vent mechanism introduced with the CORE One L is now also available on the CORE One. After updating, the feature can be enabled via Settings → Hardware → Chamber Vent Control by selecting the Auto option.

A Manual mode is also available, which keeps the vents closed by default and only shows an informational reminder before each print.

Vents can be controlled manually using the new M870 G-code ("M870 O" = open, "M870 C" = close), although we do not recommend including these commands in slicer profiles, as the printer handles vent control automatically.

The printed parts required to retrofit this feature on existing CORE One printers will be published on Printables in the coming days. A link will be added here once available.

Auto-retract improvements

The auto-retract system has been improved across the board, with particularly noticeable benefits for multi-tool prints on the XL. It now respects slicer-issued retractions and avoids adding redundant movements.

On the MK4, the print head now parks at a higher Z-height after print completion to make it easier to remove any ooze left by the auto-retract ramming process.

Auto-retract disable option

Auto-retract can now be disabled globally in the Settings menu, although this is not recommended for standard use.

It is also possible to disable auto-retract per filament type. In the filament detail menu, the former "Flexible" option has been renamed to "Auto Retract", with its behavior adjusted accordingly.

Fixed XL toolcrashes [XL]

Toolcrashes on multi-tool XL printers introduced in the alpha firmware have been fixed. The 6.4.0 firmware should now be fully functional on the XL printers.

Fixed nozzle heating for unload when auto-retracted

Printers no longer heat the nozzle for unload if the filament is auto-retracted.

Known issues

Prusa XL – Tool recovery: In some cases, triggering a tool recovery causes the print to stop responding. The nozzle and bed remain heated, but the print does not resume and cannot be recovered.

MK4S, MK4, MK3.9S, MK3.9 – The filament sensor only reacts to the first runout event during a print. Subsequent runouts are not detected until the print is restarted.

Both issues will be addressed in final release version of 6.4.0.

Full Changelog: v6.4.0-RC...v6.4.0-RC2

6.5.1 Firmware for Prusa CORE One L

Summary

• Prusa CORE One L support
• Mains-powered AC bed
• Bed fan for faster chamber heat-up
• Automatic vent opening/closing
• Redesigned error screens (BSOD/RSOD)
• Reworked filament sensor selftest
• Experimental “Fast draw” mode
• Fixed RSOD when using too little filament in MMU prints
• Allow nozzles smaller than 0.2 mm
• Allow aborting on missing sheet
• Allow continuing a single selftest
• “Shipping reset” factory reset preset
• Small UBL code refactoring #4733

This release introduces support for the new Prusa CORE One L and its unique features, including a mains-powered AC bed and automatic chamber vents. It also features a redesign of the error screens (BSOD/RSOD) and several quality-of-life improvements.

Add support for the Prusa CORE One L printer

A new printer has joined our family! This firmware adds full support for the Prusa CORE One L and its unique hardware, including the new features detailed below.

Mains-powered AC bed (C1L)

The CORE One L introduces a new AC mains-powered (120–230 V) heatbed system. This enables significantly faster heat-up times but also requires additional safety measures implemented in the firmware. The bed runs its own firmware on a dedicated processor and is the first device to communicate via the new Cyphal/CAN-based Prusa Universal Bus.

Bed fans for faster chamber heat-up (C1L)

Similar to the CORE One, the CORE One L uses the heatbed to warm up the print chamber. To speed up this process, in addition to a more powerful heatbed, we’ve added two small fans beneath the bed that circulate air inside the chamber. This improves heat distribution and allows the chamber air to absorb heat more effectively from both the top and bottom sides of the heatbed.

Automatic vent opening/closing (C1L)

The CORE One L uses a simple mechanism on the print head to automatically open and close the chamber vents. This eliminates the manual user prompts required on the non-L version.

Redesigned BSOD/RSOD

The error screens have been completely redesigned to provide a calmer, more user-friendly experience when things go wrong. The layout has been updated, and the “Blue Screen of Death”*is now the “Black Screen of Death” — still keeping the familiar BSOD acronym.

Reworked filament sensor selftest

The internal logic of the filament sensor selftest has been reworked:

• The procedure now tests the side filament sensors on all relevant printers (this was done only on the XL).
• During calibration, the printer now moves the filament up and down to gather more robust data about the “inserted” state.
• The selftest is now available on the Prusa Mini (optionally, for users who bought the sensor accessory).

Experimental “Fast draw” mode

A new “Fast draw” option in Experimental Settings significantly improves display response speed. This is an experimental feature and minor visual artifacts may occur.

Fixed RSOD when using too little filament in MMU prints

Fixed a Red Screen of Death (RSOD) that occurred in multimaterial prints using very small amounts of a single filament (e.g., < 0.3 g).

Allow nozzles smaller than 0.2 mm

It is now possible to set the nozzle diameter to 0.1 and 0.15 mm in the Hardware menu. However, using such small nozzles is only recommended for advanced users, because they lack official profiles, increase print times, and have a higher risk of clogging and layer adhesion issues.

Allow aborting on missing sheet

The “STEEL SHEET NOT DETECTED” (XX109) error now includes an “Abort” option that aborts the print, in addition to “Continue” option.

Allow continuing a single selftest

After running an individual selftest from the Calibrations & Tests menu, the “Continue running Calibrations & Tests?” prompt now includes additional options. You can now choose to:
• Continue – run only the next selftest and then be prompted again, or
• All – continue running all remaining selftests automatically.
Previously, only the Continue option was available, which always continued all remaining selftests.

“Shipping reset” factory reset preset

We are now shipping assembled CORE One L printers pre-calibrated from the factory. To support this, a new “Shipping Reset” option has been added to the Factory Reset menu. This reset type keeps the hardware configuration and calibration data, while clearing all other settings.