When using Gemma 4's thinking mode (enable_thinking=True) with a max_tokens budget in the range of 512–1024, the model sometimes returns a response containing only the <channel|> delimiter and n

Gemma 4 thinking mode draws both the reasoning chain and the answer from the same max_tokens budget. If max_tokens is too low, the thinking phase fills the context window and the model runs out of tokens before writing its answer. The <channel|> separator appears at the tail of the output or is followed by an empty string, causing any parser that splits on the marker to produce an empty result.

Fix: Set max_tokens to at least 2048 when using enable_thinking=True. For prompts that may require extended reasoning, 4096 or higher is safer.