From 3e1ceff3078ab25b84217e25cc91474cd608e3a4 Mon Sep 17 00:00:00 2001 From: Daniel Han Date: Mon, 5 Jan 2026 05:03:56 +0000 Subject: [PATCH] Sync chat_template from tokenizer to vLLM When using base models with custom chat templates applied after loading, vLLM's internal tokenizer may not have the chat_template set. This causes issues during RL training with vLLM inference. This fix syncs the chat_template from the processing_class (the tokenizer you loaded and configured) to vLLM's internal tokenizer during trainer initialization, but only if vLLM's tokenizer does not already have one set. --- unsloth/models/rl.py | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/unsloth/models/rl.py b/unsloth/models/rl.py index 88aeeda8a1..20dafaaaa4 100644 --- a/unsloth/models/rl.py +++ b/unsloth/models/rl.py @@ -694,6 +694,20 @@ def _patch_trl_rl_trainers(trainer_file = "grpo_trainer"): ) RLTrainer_post += training_check + # Sync chat_template from processing_class to vLLM's tokenizer + # This fixes base models that have custom chat templates applied after loading + if "model" in call_args: + vllm_chat_template_sync = ( + "if hasattr(self, 'llm') and self.llm is not None and hasattr(self.llm, 'get_tokenizer'):\n" + " _vllm_tok = self.llm.get_tokenizer()\n" + " _pc = getattr(self, 'processing_class', None)\n" + " if _pc is not None and getattr(_pc, 'chat_template', None) is not None:\n" + " if _vllm_tok.chat_template is None:\n" + " _vllm_tok.chat_template = _pc.chat_template\n" + "pass\n" + ) + RLTrainer_post += vllm_chat_template_sync + # Edit optional metrics other_metrics_processor = "" if trainer_file in RL_METRICS_CHANGES: