Prusa Research rolled out a matched pair of stable firmware releases on September 25, according to the GitHub release notes for version 6.10.3: one for the XL and XL+ toolchangers, and a separate build for the CORE One INDX. Both updates are incremental rather than headline-grabbing, but they address the kind of quiet, everyday friction that determines whether a multi-tool printer stays trustworthy over months of use rather than weeks.
The XL+ update, tagged v6.10.3 and built from commit bb6bbc0, was published by the GitHub account "vojtanvk" at 09:59 UTC on September 25. Its release notes list exactly two changes: "Improved chamber temperature estimation" and a reversion of "bed lowering to the previous behavior." Neither line comes with elaboration in the GitHub notes or on Prusa's own knowledge-base downloads page, which lists the same firmware under the separate XL and XL+ downloads sections, both dated September 25, 2026 (the MK4S remains on its own, older firmware line) — but both are the sort of change that matters more in practice than in a changelog bullet.
Chamber temperature estimation is a persistent challenge on enclosed multi-tool machines like the XL+, where airflow, print-head heat, and sensor placement all interact in ways that are hard to model cleanly. The XL+ doesn't rely on a single dedicated chamber thermistor the way some enclosed printers do; instead it infers chamber conditions from available sensor data, and that inference directly affects decisions like when to trigger active cooling, how aggressively to manage part cooling fans on materials sensitive to chamber heat, and whether thermal warnings fire appropriately. A refinement here, even an unglamorous one, tightens the gap between the temperature the firmware believes exists and the temperature actually inside the enclosure.
The bed-lowering reversion is more interesting for what it implies than for what it does. Reverting behavior "to the previous" state means a change introduced in an earlier release altered how or when the bed lowers — likely around print start, tool changes, or end-of-print sequences — and that alteration didn't sit well enough with either Prusa's internal testing or user feedback to keep. Neither the GitHub notes nor the knowledge-base entry specify which prior release introduced the change or what problems it caused, so the practical takeaway for owners is simpler than the diagnosis: bed movement during prints should now match what XL+ owners were used to before the regression, rather than the interim behavior.
The CORE One INDX firmware, version 6.9.1 and also dated September 25 on Prusa's downloads page, carries the more substantial changes of the two releases. The headline addition is the Square Gantry Wizard, described in the knowledge-base notes as "a standalone wizard placed just before belt tuning to verify that the screw adjustments have not skewed the gantry." On a toolchanging machine like the CORE One INDX, the gantry's squareness is foundational — if the X or Y axis frame is even slightly out of parallel, every subsequent calibration step, including belt tension tuning, is being performed against a moving target. Making the squareness check standalone and sequenced ahead of belt tuning means owners doing routine maintenance, such as adjusting frame screws after shipping, storage, or relocation, now have a dedicated tool to catch skew before it propagates into a belt-tuning pass that would otherwise compensate for the wrong problem.
Bundled with the wizard is a fix Prusa's notes label simply as "Homing Fix": adjusted motor currents intended to improve homing reliability. Homing failures on toolchanging systems tend to be quieter but more disruptive than on single-tool printers, since a missed home can misalign tool-parking positions across multiple physical toolheads rather than just one nozzle. The knowledge-base page does not specify which axis or motor was affected, but tying a current adjustment directly to homing suggests Prusa identified cases where existing current settings weren't reliably clearing the switch or triggering the sensor used for homing detection. The same 6.9.1 release also adds PVA and BVOH filament profiles, extending out-of-the-box support for the water-soluble support materials commonly paired with the CORE One's multi-material capabilities.
What It Means for Makers
For XL+ owners, 6.10.3 is a low-risk update: the chamber temperature change should make thermal behavior slightly more accurate without altering how the printer is operated, and the bed-lowering reversion undoes a change some owners may have already noticed as a regression, even without an official acknowledgment framing it that way. There's no destructive migration risk flagged in either source, so there's little reason to delay updating.
For CORE One INDX owners, 6.9.1 is worth treating as a maintenance-workflow update rather than a routine patch. The Square Gantry Wizard is explicitly meant to run before belt tuning, so anyone updating firmware ahead of a scheduled calibration pass — after moving the printer, after a frame screw adjustment, or simply as part of periodic upkeep — should run the new wizard first rather than jumping straight to belt tension. Skipping it defeats the point: a skewed gantry that goes undetected will still get "compensated for" by belt tuning in a way that doesn't actually fix the underlying geometry. The homing fix is harder for individual owners to evaluate directly, since Prusa hasn't published which specific homing failures it addresses, but anyone who has experienced inconsistent or failed homing on tool changes has a concrete reason to update and watch for improvement.
Neither knowledge-base entry nor the GitHub release notes disclose a broader roadmap, so it isn't clear from these sources alone whether the Square Gantry Wizard will eventually migrate to other Prusa multi-tool machines, or whether the chamber temperature estimation work on the XL+ is a step toward a larger thermal-management overhaul. What's confirmed is narrower and more useful in the near term: both firmware builds are live now on Prusa's downloads page, both are attributed to the same September 25 release window, and both are aimed squarely at the unglamorous reliability work — accurate sensing, correct geometry, dependable homing — that keeps multi-tool printers usable day to day.
