How do their APIs compare?

Neither of these two repositories is designed around a conventional network/web "API" in the sense of REST endpoints or SDK surfaces — they expose fundamentally different kinds of interfaces suited to their purposes.

microsoft/bitnet (bitnet.cpp) This is an inference framework, so its "API" is primarily:

• Command-line / script interfaces for benchmarking, conversion, and evaluation — e.g. the benchmark shell script driving llama-bench with model paths and thread counts [docs/bitnet-embeddings-i2s-guide.md:L418-L445], and evaluation scripts like eval_mmteb_v2.py invoked with --model-dir, --f16-gguf, --build-dir, etc. [docs/bitnet-embeddings-i2s-guide.md:L278-L300].
• Python utility modules with functions for specific tasks, such as quantize_embeddings.py's log-parsing logic that extracts thread counts and throughput values from benchmark output [utils/quantize_embeddings.py:L217-L256], or convert-bitnet-embedding-to-gguf.py's _does_token_look_special helper for tokenizer special-token detection [utils/convert-bitnet-embedding-to-gguf.py:L164-L173].
• Low-level C++ kernel code generation — codegen_tl2.py emits raw AVX2 intrinsics (_mm256_*) for quantized matrix-vector kernels [utils/codegen_tl2.py:L205-L244, L359-L398]. This isn't a stable public API; it's internal codegen for performance-critical inference paths.

There's no evidence in the retrieved data of a formal HTTP/REST API, request validation layer, or versioned SDK contract — the interface surface is scripts, CLI flags, and C++ functions tied to GGUF model files and quantization formats (I2_S, TL2, etc.).

notepad-plus-plus/notepad-plus-plus This exposes a genuine plugin API intended for third-party consumers:

• PluginInterface.h defines the exported C-linkage functions plugins can call/implement, e.g. isUnicode() [PowerEditor/src/MISC/PluginsManager/PluginInterface.h:L71-L74].
• PluginsManager.cpp implements version-compatibility negotiation between plugin DLLs and the host editor, using a Version class with comparison operators (isCompatibleTo, compareTo) to decide whether a plugin's declared Notepad++ compatibility range matches the running version, including fallback logic for older plugin versions via _oldVersionCompatibility [PowerEditor/src/MISC/PluginsManager/PluginsManager.cpp:L386-L425].
• The Version class itself, in Common.h, provides the comparison/equality operators and isCompatibleTo used throughout this negotiation [PowerEditor/src/MISC/Common/Common.h:L211-L285].
• Notepad_plus.h/.cpp is the central editor class aggregating subsystems (docking, tabs, find/replace, plugins manager) but is internal application structure, not a public API [PowerEditor/src/Notepad_plus.h:L1-L40, PowerEditor/src/Notepad_plus.cpp:L1-L40].

Comparison summary

• bitnet's "API" is oriented toward ML practitioners: CLI scripts and Python functions for quantizing, converting, and benchmarking models — no stable ABI/versioning contract shown in this data.
• notepad-plus-plus's API is oriented toward plugin developers: a formal, versioned C++ plugin interface with explicit compatibility-checking machinery (Version, PluginsManager) to keep third-party DLLs working across editor releases.

If you want, I can dig deeper into either bitnet's Python conversion/quantization function signatures or the full PluginInterface.h contract (message/notification functions) for a more granular comparison.

FOLLOW_UPS:

• What functions does PluginInterface.h expose to plugins?
• How does bitnet's I2_S quantization format work?
• What does Notepad++'s Version compatibility check enforce?