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AI models continue to improve over time. Newer models generally offer improvements in areas such as reasoning, instruction following, speed, and efficiency.
Availability: Model migration is available on all plans. The models you can migrate to depend on your plan. See Choose your AI model for model availability.
AI models continue to improve over time. Newer models generally offer improvements in areas such as reasoning, instruction following, speed, and efficiency. Older models may eventually be retired from Watermelon. When Watermelon retires a model, affected customers will receive a migration deadline. Keeping your Agent on a recommended model helps you benefit from newer improvements and reduces the chance that you need to migrate under time pressure. Important: Changing your AI model can change how your Agent interprets and follows the same prompts. Always review and test your Agent after switching models.

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Which model should I migrate to?

For most Agents, we recommend GPT-5.6 Luna. For more complex use cases that require stronger reasoning, GPT-5.4 mini may be a better fit. See Choose your AI model for our recommendations and model availability per plan.

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1. Review your Agent Settings and Instructions

Different AI models can interpret the same prompt differently. An Instruction that worked well with your previous model may be followed differently after switching. Before changing your model, review your existing Agent Settings and Instructions. A useful way to do this is with ChatGPT. Copy your Agent Settings and Instructions into ChatGPT and use a prompt such as:
These are my current Agent Settings and Instructions for GPT-[current model]. I want to migrate to GPT-[new model]. Review them for compatibility with the new model and make only the changes needed to keep the existing behaviour and business rules consistent. Make the wording clear and specific, but do not add, remove, or change any business rules. Explain any changes you recommend.
Review the suggested changes before adding them to Watermelon. ChatGPT can help restructure your prompts, but you should always make sure that important business rules and intended behaviour have not changed.

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2. Change your AI model

Once you have reviewed your Agent Settings and Instructions:
  1. Open your Agent.
  2. Open the AI model setting.
  3. Select your new model.
  4. Save your changes.
You do not need to create a new Agent. Your Agent Settings, Instructions, and Sources remain in place when you change the model.

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3. Test your Agent

Do not assume that your Agent will behave exactly the same after switching models. Open the Playground and test the scenarios that are most important to your use case. We recommend using real customer questions from your Inbox and testing:
  • Frequently asked questions
  • Important Instructions
  • Conversation flows
  • Conditions and exceptions
  • Actions, where relevant
  • Human handovers
  • Tone of voice
  • Language behaviour, if relevant
Pay particular attention to Instructions that must always be followed. If something behaves differently, start by reviewing the relevant Agent Setting or Instruction and making it clearer and more specific. Avoid adding several overlapping Instructions to solve the same problem, as this can make your Agent harder to maintain.

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4. Keep your model up to date

You do not need to change your model every time a new model becomes available. However, we recommend regularly checking whether your Agent still uses one of Watermelon’s recommended models. Newer models are generally improved versions of previous generations and can offer better reasoning, instruction following, speed, or efficiency. Older models are also more likely to be retired over time. If Watermelon schedules your model for retirement, we will communicate a deadline. Make sure you migrate and test your Agent before that date to prevent disruption.