BFloat16 logits returned as garbage — Logits::Get() only casts Float16 to float32

### Describe the bug For models with **BFloat16** logits output, `onnxruntime-genai` returns garbage logits, producing a wrong/incoherent first token and degenerate generation. The identical model exported in **Float16** works correctly. ### Root cause `src/models/logits.cpp` (`Logits::Get()`) only converts the model's raw logits to `float32` when the output type is **Float16**. For **BFloat16** it skips the conversion, then `WrapTensor<float>(...)` reinterprets the raw 2-byte bf16 bytes as 4-byte float32, corrupting every logit. Two places are gated on `Float16` only: ```cpp // ~line 47 — fp32 staging buffer is allocated only for Float16 if (type_ == Ort::TypeToTensorType<Ort::Float16_t>) logits_of_last_token_fp32_ = OrtValue::CreateTensor<float>(...); // ~line 73 — Cast to float32 runs only for Float16 if (type_ == Ort::TypeToTensorType<Ort::Float16_t>) { Cast(*logits_of_last_token, logits_of_last_token_fp32_, *model_.p_device_inputs_, Ort::TypeToTensorType<float>); logits_of_last_token = logits_of_last_token_fp32_.get(); } ``` For a bf16 model the `Cast` never runs, so `logits_` ends up wrapping raw bf16 bytes as `float`. ### How I verified Isolated a bf16 vs fp16 model (Gemma-style decoder, vocab 262144): - HF bf16 reference, raw ORT `sess.run` of the bf16 decoder, and genai's own dumped model-output logits **all agree** (argmax 496, top-5 `[496,886,506,9079,992]`). - genai's `get_logits()` for the **same** bf16 model returns argmax 4539 — a value that does **not** correspond to any position in the model's actual output. The corruption is purely in the logits read-out, not the model compute or the ORT kernels. ### Proposed fix Treat `BFloat16` the same as `Float16` in both spots, and add a bf16→f32 conversion path. The existing `Cast()` helper already falls back to a CPU bf16→f32 cast; I also added a CUDA `LaunchBf16ToFp32` kernel so the cast stays on-device. ```diff --- a/src/models/logits.cpp +++ b/src/models/logits.cpp - if (type_ == Ort::TypeToTensorType<Ort::Float16_t>) + if (type_ == Ort::TypeToTensorType<Ort::Float16_t> || type_ == Ort::TypeToTensorType<Ort::BFloat16_t>) logits_of_last_token_fp32_ = OrtValue::CreateTensor<float>(...); ... - // Convert from float16 to float32 if necessary - if (type_ == Ort::TypeToTensorType<Ort::Float16_t>) { + // Convert from float16/bfloat16 to float32 if necessary + if (type_ == Ort::TypeToTensorType<Ort::Float16_t> || type_ == Ort::TypeToTensorType<Ort::BFloat16_t>) { Cast(*logits_of_last_token, logits_of_last_token_fp32_, *model_.p_device_inputs_, Ort::TypeToTensorType<float>); logits_of_last_token = logits_of_last_token_fp32_.get(); } ``` Plus a CUDA bf16→f32 case (`src/cuda/interface.cpp` `Cast`, `src/cuda/model_kernels.cu` / `kernels.h` `LaunchBf16ToFp32`). After the fix, the bf16 model's first-token argmax is 496 (matches HF/fp16) and generation is byte-identical to fp16. ### Urgency Medium — blocks deploying any bf16 model via genai. fp16 is an available workaround but loses bf16's wider dynamic range. ### Platform / Version - onnxruntime-genai built from source, CUDA EP, Linux. - Reproduces independent of EP/kernel dispatch (model compute is correct; only the logits read-out is affected). I have a tested fix and can open a PR if useful.