diff --git a/README.md b/README.md
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+++ b/README.md
@@ -20,6 +20,7 @@ If you find this fun or interesting!
 **This fork is currently in active development and has been tested on actual hardware.**
 
 - **Use at Your Own Risk**: As with any slicer fork, please review critical prints and generated G-code before production use
+- **Project Compatibility Warning**: Some `.3mf` files created with older FullSpectrum builds may not open or migrate cleanly in newer versions because mixed-filament data and project serialization have changed over time
 
 ---
 
diff --git a/doc/changelogs/CHANGELOG_v0.9.51.md b/doc/changelogs/CHANGELOG_v0.9.51.md
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@@ -0,0 +1,41 @@
+# Snapmaker Orca FullSpectrum v0.9.51
+
+Mixed-filament bias controls, preview updates, and release cleanup.
+Based on Snapmaker Orca v2.3.1.
+
+## Highlights
+
+### Mixed Filament Bias
+- Added an optional per-pair **Bias** control for mixed filaments.
+- Positive bias recesses the second filament in the pair.
+- Negative bias recesses the first filament in the pair.
+- Added clamping and signed-bias handling so the slicer and UI use the same safe range.
+
+### Mixed Filament Workflow Improvements
+- Added a print setting to enable or disable mixed-filament bias mode.
+- Moved the bias control inline with the mixed-filament preview row to keep the editor compact.
+- Added apparent-color preview feedback so biased pairs can show an estimated shifted mix in the UI.
+- Simplified the final bias workflow so the control behaves consistently across mixed filament pairs.
+
+### Slicing And Preview Fixes
+- Applied bias through the mixed-filament slicing path so recessed layers affect generated geometry instead of only the editor preview.
+- Fixed mixed-filament panel refresh behavior when the bias setting is toggled.
+- Improved preview behavior for biased mixed filaments and reduced mismatches between the row preview and sliced output.
+- Fixed region handling so recessed mixed-filament space is not immediately refilled by the other component in the common painted path.
+
+### Release And Project Maintenance
+- Bumped the FullSpectrum version to `0.9.51`.
+- Moved older changelogs and release notes into `doc/changelogs/` and updated the release workflow to read them from there.
+- Refreshed the README mixed-filament section to document the Bias feature and added a compatibility warning for older `.3mf` projects.
+
+## Tests
+
+- Expanded `test_mixed_filament.cpp` coverage for signed bias, clamping, serialization, and remapping behavior.
+- Rebuilt `libslic3r_gui`.
+- Rebuilt `libslic3r_tests` and re-ran the `[MixedFilament]` suite successfully.
+
+## Important Notes
+
+- Some `.3mf` files created with older FullSpectrum builds may not load or migrate cleanly in newer versions because mixed-filament project data has evolved.
+- macOS builds from this fork remain unsigned and not notarized.
+- Use at your own risk.