messages_turn_1 = [{"role": "user", "content": "What is the capital of France?"}]
messages_turn_2 = [{"role": "system", "content": "Today is Tuesday."},
                   {"role": "user", "content": "What is the capital of France?"}]

# tokenize=True is the default and returns a plain list of token ids
a = tokenizer.apply_chat_template(messages_turn_1)
b = tokenizer.apply_chat_template(messages_turn_2)

shared = 0
for x, y in zip(a, b):
    if x != y:
        break
    shared += 1

print(f"shared prefix: {shared} tokens of {len(a)} and {len(b)}")
print(f"first divergence at index {shared}: {a[shared:shared+8]} vs {b[shared:shared+8]}")

# Output:
"""
shared prefix: 3 tokens of 35 and 26
diverges at index 3
  turn 1: [2683, 418, 253, 11173, 9042, 14260] You are a helpful AI assistant
  turn 2: [11814, 314, 27758, 30, 2, 198] Today is Tuesday.<|im_end|>
"""