It works in GPT-4 (but not GPT-3.5) even without a special tokenizer: Some problems simply solve themselves with increasing scale. But Bard uses a smaller LaMDA model to reduce inference cost. Quote [1] from Sundar Pichai in February:

> We’re releasing it initially with our lightweight model version of LaMDA. This much smaller model requires significantly less computing power, enabling us to scale to more users, allowing for more feedback.

[1] https://blog.google/technology/ai/bard-google-ai-search-upda...