diff --git a/.gitmodules b/.gitmodules
index 80308f05..7c0ed75c 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,4 @@
-[submodule "open-x4-sdk"]
-	path = open-x4-sdk
-	url = https://github.com/crosspoint-reader/community-sdk.git
+[submodule "freeink-sdk"]
+	path = freeink-sdk
+	url = https://github.com/Free-Ink/freeink-sdk.git
+	branch = main
diff --git a/.skills/SKILL.md b/.skills/SKILL.md
index 9ebda0a1..55e72d23 100644
--- a/.skills/SKILL.md
+++ b/.skills/SKILL.md
@@ -7,7 +7,7 @@ Mission: Provide a lightweight, high-performance reading experience focused on E
 * Role: Senior Embedded Systems Engineer (ESP-IDF/Arduino-ESP32 specialized).
 * Primary Constraint: 380KB RAM is the hard ceiling. Stability is non-negotiable.
 * Evidence-Based Reasoning: Before proposing a change, you MUST cite the specific file path and line numbers that justify the modification.
-* Anti-Hallucination: Do not assume the existence of libraries or ESP-IDF functions. If you are unsure of an API's availability for the ESP32-C3 RISC-V target, check the open-x4-sdk or official docs first.
+* Anti-Hallucination: Do not assume the existence of libraries or ESP-IDF functions. If you are unsure of an API's availability for the ESP32-C3 RISC-V target, check the freeink-sdk source or the FreeInk SDK docs (https://freeink.org/llms.txt for an LLM-readable index) first.
 * No Unfounded Claims: Do not claim performance gains or memory savings without explaining the technical mechanism (e.g., DRAM vs IRAM usage).
 * Resource Justification: You must justify any new heap allocation (new, malloc, std::vector) or explain why a stack/static alternative was rejected.
 * Verification: After suggesting a fix, instruct the user on how to verify it (e.g., monitoring heap via Serial or checking a specific cache file).
@@ -127,7 +127,7 @@ These flags in `platformio.ini` fundamentally affect firmware behavior:
   * lib/hal/: Hardware Abstraction Layer (HalDisplay, HalGPIO, HalStorage)
   * lib/I18n/: Internationalization (translations in `translations/*.yaml`, generated string tables)
 * src/activities/: UI logic using the Activity Lifecycle (onEnter, loop, onExit)
-* open-x4-sdk/: Low-level SDK (EInkDisplay, InputManager, BatteryMonitor, SDCardManager)
+* freeink-sdk/: Low-level SDK (EInkDisplay, InputManager, BatteryMonitor, SDCardManager)
 * .crosspoint/: SD-based binary cache for EPUB metadata and pre-rendered layout sections
 
 ### Hardware Abstraction Layer (HAL)
diff --git a/bin/clang-format-fix.ps1 b/bin/clang-format-fix.ps1
index f90a81b7..28e9394c 100644
--- a/bin/clang-format-fix.ps1
+++ b/bin/clang-format-fix.ps1
@@ -4,7 +4,7 @@
 
 .DESCRIPTION
     Formats all C/C++ source and header files in the repository, excluding
-    generated, vendored, and build directories (open-x4-sdk, builtinFonts,
+    generated, vendored, and build directories (freeink-sdk, builtinFonts,
     hyphenation tries, uzlib, .pio, *.generated.h).
 
     The clang-format binary path is resolved once and cached in
@@ -92,7 +92,7 @@ function Resolve-ClangFormat {
 $clangFormat = Resolve-ClangFormat
 
 $exclude = @(
-    'open-x4-sdk'
+    'freeink-sdk'
     'lib\EpdFont\builtinFonts'
     'lib\Epub\Epub\hyphenation\generated'
     'lib\uzlib'
diff --git a/docs/contributing/architecture.md b/docs/contributing/architecture.md
index 3e1729a5..b0a85056 100644
--- a/docs/contributing/architecture.md
+++ b/docs/contributing/architecture.md
@@ -8,7 +8,7 @@ At a high level, it is firmware that uses an activity-driven application archite
 
 ```mermaid
 graph TD
-    A[Hardware: ESP32-C3 + SD + E-ink + Buttons] --> B[open-x4-sdk]
+    A[Hardware: ESP32-C3 + SD + E-ink + Buttons] --> B[freeink-sdk]
     B --> C[lib/hal wrappers]
     C --> D[src/main.cpp runtime loop]
     D --> E[Activities layer]
@@ -195,10 +195,10 @@ When editing related source assets, regenerate via normal build steps/scripts.
 - `src/`: app orchestration, settings/state, and activity implementations
 - `src/network/`: web server and OTA/update networking
 - `src/components/`: theming and shared UI components
-- `lib/hal/`: hardware abstraction wrappers around open-x4-sdk
+- `lib/hal/`: hardware abstraction wrappers around freeink-sdk
 - `lib/Epub/`: EPUB parser, layout, CSS handling, and hyphenation
 - `lib/`: supporting libraries (fonts, text, filesystem helpers, etc.)
-- `open-x4-sdk/`: hardware SDK submodule (display, input, storage, battery)
+- `freeink-sdk/`: hardware SDK submodule (display, input, storage, battery). Docs: https://freeink.org/docs
 - `docs/`: user and technical documentation
 
 ## Embedded constraints that shape design
diff --git a/freeink-sdk b/freeink-sdk
new file mode 160000
index 00000000..8be32366
--- /dev/null
+++ b/freeink-sdk
@@ -0,0 +1 @@
+Subproject commit 8be32366091e3e0eadeda9b983091166140f816f
diff --git a/open-x4-sdk b/open-x4-sdk
deleted file mode 160000
index 198ad267..00000000
--- a/open-x4-sdk
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit 198ad267219c25c8ab84418b806c66f1fb5216a3
diff --git a/platformio.ini b/platformio.ini
index 0fae0516..03a2ece2 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -35,6 +35,8 @@ build_flags =
 # Increase PNG scanline buffer to support up to 2048px wide images
 # Default is (320*4+1)*2=2562, we need more for larger images
   -DPNG_MAX_BUFFERED_PIXELS=16416
+  -DFREEINK_DEVICE_X4=1
+  -DFREEINK_DEVICE_X3=1
   -Wno-bidi-chars
   -Wl,--wrap=panic_print_backtrace,--wrap=panic_abort,--wrap=bootloader_common_check_efuse_blk_validity
   -fno-exceptions
@@ -57,10 +59,14 @@ extra_scripts =
 
 ; Libraries
 lib_deps =
-  BatteryMonitor=symlink://open-x4-sdk/libs/hardware/BatteryMonitor
-  InputManager=symlink://open-x4-sdk/libs/hardware/InputManager
-  EInkDisplay=symlink://open-x4-sdk/libs/display/EInkDisplay
-  SDCardManager=symlink://open-x4-sdk/libs/hardware/SDCardManager
+  BatteryMonitor=symlink://freeink-sdk/libs/hardware/BatteryMonitor
+  InputManager=symlink://freeink-sdk/libs/hardware/InputManager
+  EInkDisplay=symlink://freeink-sdk/libs/display/FreeInkDisplay
+  SDCardManager=symlink://freeink-sdk/libs/hardware/SDCardManager
+  BoardConfig=symlink://freeink-sdk/libs/hardware/BoardConfig
+  PowerManager=symlink://freeink-sdk/libs/hardware/PowerManager
+  FreeInkUI=symlink://freeink-sdk/libs/ui/FreeInkUI
+  Icons=symlink://freeink-sdk/libs/assets/Icons
   bblanchon/ArduinoJson @ 7.4.2
   ricmoo/QRCode @ 0.0.1
   bitbank2/PNGdec @ 1.1.6