diff --git a/.claude/commands/upgrade-pylib.md b/.claude/commands/upgrade-pylib.md
new file mode 100644
index 00000000000..520d5deb7ba
--- /dev/null
+++ b/.claude/commands/upgrade-pylib.md
@@ -0,0 +1,32 @@
+# Upgrade Python Library from CPython
+
+Upgrade a Python standard library module from CPython to RustPython.
+
+## Arguments
+- `$ARGUMENTS`: Library name to upgrade (e.g., `inspect`, `asyncio`, `json`)
+
+## Steps
+
+1. **Delete existing library in Lib/**
+   - If `Lib/$ARGUMENTS.py` exists, delete it
+   - If `Lib/$ARGUMENTS/` directory exists, delete it
+
+2. **Copy from cpython/Lib/**
+   - If `cpython/Lib/$ARGUMENTS.py` exists, copy it to `Lib/$ARGUMENTS.py`
+   - If `cpython/Lib/$ARGUMENTS/` directory exists, copy it to `Lib/$ARGUMENTS/`
+
+3. **Upgrade tests**
+   - Run: `python lib_updater.py --quick-upgrade cpython/Lib/test/test_$ARGUMENTS`
+   - This will update the test files with appropriate RustPython markers
+
+## Example Usage
+```
+/upgrade-pylib inspect
+/upgrade-pylib json
+/upgrade-pylib asyncio
+```
+
+## Notes
+- The cpython/ directory should contain the CPython source that we're syncing from
+- lib_updater.py handles adding `# TODO: RUSTPYTHON` markers and `@unittest.expectedFailure` decorators
+- After upgrading, you may need to run tests to verify: `cargo run --release -- -m test test_$ARGUMENTS`
diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index a2ab43a695c..4667f4ee17b 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -87,11 +87,14 @@ rm -r target/debug/build/rustpython-* && find . | grep -E "\.pyc$" | xargs rm -r
 # Run Rust unit tests
 cargo test --workspace --exclude rustpython_wasm
 
-# Run Python snippets tests
+# Run Python snippets tests (debug mode recommended for faster compilation)
+cargo run -- extra_tests/snippets/builtin_bytes.py
+
+# Run all Python snippets tests with pytest
 cd extra_tests
 pytest -v
 
-# Run the Python test module
+# Run the Python test module (release mode recommended for better performance)
 cargo run --release -- -m test ${TEST_MODULE}
 cargo run --release -- -m test test_unicode # to test test_unicode.py
 
@@ -99,6 +102,8 @@ cargo run --release -- -m test test_unicode # to test test_unicode.py
 cargo run --release -- -m test test_unicode -k test_unicode_escape
 ```
 
+**Note**: For `extra_tests/snippets` tests, use debug mode (`cargo run`) as compilation is faster. For `unittest` (`-m test`), use release mode (`cargo run --release`) for better runtime performance.
+
 ### Determining What to Implement
 
 Run `./whats_left.py` to get a list of unimplemented methods, which is helpful when looking for contribution opportunities.
@@ -184,6 +189,12 @@ cargo build --target wasm32-wasip1 --no-default-features --features freeze-stdli
 cargo run --features jit
 ```
 
+### Building venvlauncher (Windows)
+
+See DEVELOPMENT.md "CPython Version Upgrade Checklist" section.
+
+**IMPORTANT**: All 4 venvlauncher binaries use the same source code. Do NOT add multiple `[[bin]]` entries to Cargo.toml. Build once and copy with different names.
+
 ## Test Code Modification Rules
 
 **CRITICAL: Test code modification restrictions**