Fix context length exceeded error Claude
Quick answer
The
context length exceeded error in Claude occurs when the total tokens in your conversation exceed the model's maximum context window. To fix it, truncate or summarize earlier messages to stay within the token limit before sending your request. ERROR TYPE
api_error ⚡ QUICK FIX
Trim or summarize your conversation history to keep total tokens within Claude's context window before calling the API.
Why this happens
The context length exceeded error occurs because Claude models have a fixed maximum token limit for the entire conversation context, including system, user, and assistant messages. If your combined messages exceed this limit, the API rejects the request with this error.
For example, if you send a long chat history or a very large prompt, the total tokens can surpass Claude's context window (e.g., 100k tokens for claude-3-5-sonnet-20241022 or smaller for earlier versions).
Typical error output:
{
"error": {
"message": "Context length exceeded",
"type": "invalid_request_error"
}
}Broken code example sending too long messages:
import anthropic
import os
client = anthropic.Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])
messages = [
{"role": "user", "content": "Very long conversation or document..." * 10000}
]
response = client.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1024,
system="You are a helpful assistant.",
messages=messages
)
print(response.content[0].text) output
{
"error": {
"message": "Context length exceeded",
"type": "invalid_request_error"
}
} The fix
To fix the error, reduce the total tokens in your conversation context. This can be done by:
- Trimming or summarizing earlier messages in the chat history.
- Splitting large inputs into smaller chunks and processing them sequentially.
Example fixed code truncating messages to fit context window:
import anthropic
import os
client = anthropic.Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])
# Function to truncate messages to a safe token count (pseudo-code)
def truncate_messages(messages, max_tokens=80000):
# Implement token counting and truncate older messages
# Here we just keep the last message for simplicity
return messages[-1:]
messages = [
{"role": "user", "content": "Very long conversation or document..." * 10000}
]
truncated_messages = truncate_messages(messages)
response = client.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1024,
system="You are a helpful assistant.",
messages=truncated_messages
)
print(response.content[0].text) output
Assistant response text here Status: 200
Preventing it in production
To avoid context length errors in production:
- Implement token counting on your client side before sending requests.
- Use conversation summarization to compress chat history.
- Apply sliding window techniques to keep recent context only.
- Use retries with backoff if you detect context errors.
- Monitor token usage and warn users when inputs are too large.
Key Takeaways
- Claude models have fixed token limits; exceeding them causes context length errors.
- Always truncate or summarize conversation history to fit within the model's context window.
- Implement token counting and sliding window context management in production.
- Use retries and monitoring to handle and prevent context-related API errors.