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Check prefix preservation at the token level #5559

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Merged
qgallouedec merged 8 commits into from
Apr 20, 2026
Merged

Check prefix preservation at the token level #5559

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7258c00
Check prefix preservation at the token level
qgallouedec Apr 15, 2026
a076c4a
fix vml
qgallouedec Apr 15, 2026
84e90a0
fix vlm
qgallouedec Apr 16, 2026
22dc962
Merge branch 'main' into check-prefix-preservation-at-the-token-level
qgallouedec Apr 16, 2026
af51127
Merge branch 'main' into check-prefix-preservation-at-the-token-level
qgallouedec Apr 17, 2026
5f3f91b
fix
qgallouedec Apr 17, 2026
d3f2474
rm duplicate
qgallouedec Apr 17, 2026
723c064
Merge branch 'main' into check-prefix-preservation-at-the-token-level
qgallouedec Apr 20, 2026
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10 changes: 5 additions & 5 deletions trl/chat_template_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -420,18 +420,18 @@ def is_chat_template_prefix_preserving(tokenizer: PreTrainedTokenizer) -> bool:
]

try:
text1 = tokenizer.apply_chat_template(messages1, tokenize=False)
text2 = tokenizer.apply_chat_template(messages2, tokenize=False, add_generation_prompt=True)
ids1 = tokenizer.apply_chat_template(messages1, tokenize=True, return_dict=False)
ids2 = tokenizer.apply_chat_template(messages2, tokenize=True, return_dict=False, add_generation_prompt=True)
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except TypeError:
# Best-effort fallback for templates that reject dict args (e.g. DeepSeek-V3). This is a chat template
# bug (see transformers#45419), and the training chat template fixes it to avoid blocking users.
dummy_tool_calls = [{"type": "function", "function": {"name": "dummy", "arguments": "{}"}}]
messages1[1]["tool_calls"] = dummy_tool_calls
messages2[1]["tool_calls"] = dummy_tool_calls
text1 = tokenizer.apply_chat_template(messages1, tokenize=False)
text2 = tokenizer.apply_chat_template(messages2, tokenize=False, add_generation_prompt=True)
ids1 = tokenizer.apply_chat_template(messages1, tokenize=True, return_dict=False)
ids2 = tokenizer.apply_chat_template(messages2, tokenize=True, return_dict=False, add_generation_prompt=True)
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return text2.startswith(text1)
return ids2[: len(ids1)] == ids1
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deepseekv3_training_chat_template = (_CHAT_TEMPLATES_DIR / "deepseekv3_training.jinja").read_text()
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