feat: support override HF model name in convert_megatron_to_hf (#2202)

Signed-off-by: Dhineshkumar Ramasubbu <dhineshkumar.ramasubbu@gmail.com>

Author: dhineshkumar-r

docs/design-docs/checkpointing.md

@@ -22,10 +22,17 @@ rsync -ahP $CKPT_DIR/policy/tokenizer ${CKPT_DIR}-hf/
 
 ## Converting Megatron Checkpoints to Hugging Face Format
 
-For models that were originally trained using the Megatron-LM backend, a separate converter is available to convert Megatron checkpoints to Hugging Face format. This script requires Megatron-Core, so make sure to launch the conversion with the `mcore` extra. For example,
+For models that were originally trained using the Megatron-LM backend, a separate converter is available to convert Megatron checkpoints to Hugging Face format. This script requires Megatron-Core, so make sure to launch the conversion with the `mcore` extra. 
 
+Use `--hf-model-name` argument to override the model name mentioned in `config.yaml`. This is useful for models like GPT-OSS whose base checkpoint precision(mxfp4) is different from supported export precision(bfloat16) in Megatron-Bridge, [Ref](https://github.com/NVIDIA-NeMo/Megatron-Bridge/tree/main/examples/models/gpt_oss).
+
+For example,
 ```sh
 CKPT_DIR=results/sft/step_10
 
-uv run --extra mcore examples/converters/convert_megatron_to_hf.py --config=$CKPT_DIR/config.yaml --megatron-ckpt-path=$CKPT_DIR/policy/weights/iter_0000000/ --hf-ckpt-path=<path_to_save_hf_ckpt>
+uv run --extra mcore examples/converters/convert_megatron_to_hf.py \
+  --config=$CKPT_DIR/config.yaml \
+  --hf-model-name <repo>/model_name \
+  --megatron-ckpt-path=$CKPT_DIR/policy/weights/iter_0000000/ \
+  --hf-ckpt-path=<path_to_save_hf_ckpt>
 ```

examples/converters/convert_megatron_to_hf.py

@@ -21,6 +21,7 @@
 """ NOTE: this script requires mcore. Make sure to launch with the mcore extra:
 uv run --extra mcore python examples/converters/convert_megatron_to_hf.py \
   --config <path_to_ckpt>/config.yaml \
+  --hf-model-name <repo>/model_name \
   --megatron-ckpt-path <path_to_ckpt>/policy/weights/iter_xxxxx \
   --hf-ckpt-path <path_to_save_hf_ckpt>
 """
@@ -37,6 +38,12 @@ def parse_args():
         default=None,
         help="Path to config.yaml file in the checkpoint directory",
     )
+    parser.add_argument(
+        "--hf-model-name",
+        type=str,
+        default=None,
+        help="HuggingFace model name override",
+    )
     parser.add_argument(
         "--megatron-ckpt-path",
         type=str,
@@ -59,7 +66,10 @@ def main():
     with open(args.config, "r") as f:
         config = yaml.safe_load(f)
 
-    model_name = config["policy"]["model_name"]
+    # Use hf_model_name override, if available.
+    model_name = (
+        args.hf_model_name if args.hf_model_name else config["policy"]["model_name"]
+    )
     tokenizer_name = config["policy"]["tokenizer"]["name"]
     hf_overrides = config["policy"].get("hf_overrides", {}) or {}