What is multi-turn conversation handling in Claude and how do you implement it?

Claude's Messages API is stateless — each API call is independent and Claude has no memory of previous calls unless you include the conversation history explicitly. Multi-turn conversation is implemented by appending each exchange to the messages array.

# Building a multi-turn conversation manually
messages = []

# Turn 1
messages.append({"role": "user", "content": "What is the capital of France?"})
response = client.messages.create(
    model="claude-opus-4-8",
    max_tokens=256,
    messages=messages
)
assistant_reply = response.content[0].text
messages.append({"role": "assistant", "content": assistant_reply})

# Turn 2 — Claude now has context of the previous exchange
messages.append({"role": "user", "content": "What is its population?"})
response2 = client.messages.create(
    model="claude-opus-4-8",
    max_tokens=256,
    messages=messages  # full history included
)
print(response2.content[0].text)
# Claude knows "its" refers to Paris from the previous turn

# Important: as conversation grows, context window fills up
# Common strategies when context limit approaches:
# 1. Summarise older turns and replace them with the summary
# 2. Use prompt caching on stable early context
# 3. Truncate oldest messages (may lose important context)

Key implementation notes:

• Messages must alternate: user → assistant → user → assistant (etc.)
• You cannot have two consecutive user or assistant messages
• The entire conversation history is sent on every request — this grows your token count over time
• Prompt caching can significantly reduce costs for long conversations with stable early context

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