ollama - 💡(How to fix) Fix ollama launch claude - wrong model context window [4 comments, 2 participants]

time=2026-03-22T18:17:43.929Z level=WARN source=runner.go:187 msg="truncating input prompt" limit=32768 prompt=55247 keep=4 new=32768

Fix Plan

The issue is caused by the context window being filled up, causing Claude to not recognize the model's context. To fix this, we need to increase the context window size or implement a mechanism to manage the context window size dynamically.

Here are the steps to fix the issue:

• Increase the context window size by setting the CONTEXT_WINDOW_SIZE environment variable:
  • Run the following command: export CONTEXT_WINDOW_SIZE=65536
• Alternatively, you can modify the ollama configuration file to increase the context window size:
  • Add the following line to the ollama.cfg file: context_window_size = 65536
• If you want to implement a dynamic context window size management, you can modify the runner.go file to truncate the input prompt based on the available context window size:
  • Modify the truncating input prompt logic in the runner.go file to use a dynamic threshold based on the available context window size

Example code snippet to modify the runner.go file:

// ...
if len(prompt) > contextWindowSize {
    // Calculate the available context window size
    availableWindowSize := contextWindowSize - len(systemPrompt) - len(systemTools) - len(mcpTools) - len(customAgents) - len(skills) - len(messages)
    // Truncate the input prompt based on the available context window size
    prompt = prompt[:availableWindowSize]
    log.Warn("truncating input prompt", zap.Int("limit", availableWindowSize), zap.Int("keep", 4), zap.Int("new", availableWindowSize))
}
// ...

Verification

To verify that the fix worked, you can:

• Check the context window usage by running the ollama ps command
• Verify that the context window size has been increased by checking the ollama.cfg file or the environment variable CONTEXT_WINDOW_SIZE
• Test the dynamic context window size management by filling up the context window and verifying that the input prompt is truncated correctly

Extra Tips

• Make sure to update the ollama version to the latest version to ensure that you have the latest fixes and features.
• Consider implementing a mechanism to monitor the context window size and alert when it reaches a certain threshold to prevent issues like this in the future.