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What is Fast Apply?

Fast Apply is a feature that enables instant code edits with high accuracy by leveraging specialized “apply models” from Morph. It replicates Cursor AI’s instant apply functionality, allowing for seamless code modifications without the typical delays of traditional code generation.
Fast Apply uses the specialized Morph API for instant code merging. This is separate from your main AI provider.

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Why Fast Apply?

Traditional AI code generation has noticeable latency:
  1. Slow application: Full language models take time to generate and apply changes
  2. Merge errors: Generic models struggle with accurate code merging
  3. Context overhead: Large context windows slow down simple edits
Fast Apply solves this:
  • ✅ Instant application: Code changes applied immediately without delays
  • ✅ High accuracy: 96-98% accuracy for code edits
  • ✅ Blazing speed: 2500-4500+ tokens per second
  • ✅ Large context: Handles up to 16k tokens for input and output

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How It Works

Instead of using a general-purpose LLM to both generate and apply code:
  1. Your main AI provider (Claude, GPT, etc.) generates the edit instructions
  2. The specialized Morph apply model merges changes instantly
  3. Changes appear in your editor without noticeable delay

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Setup

1

Get a Morph API key

Visit morphllm.com and create an account.Generate an API key from the dashboard.
2

Set the API key

Add to your shell configuration:
export MORPH_API_KEY="your-api-key"
Then reload:
source ~/.bashrc  # or ~/.zshrc
3

Enable Fast Apply

Configure Avante to use Fast Apply:
require('avante').setup({
  behaviour = {
    enable_fastapply = true,  -- Enable Fast Apply
  },
})
4

Choose your model (optional)

Select which Morph model to use:
require('avante').setup({
  behaviour = {
    enable_fastapply = true,
  },
  providers = {
    morph = {
      model = "morph-v3-large",  -- or "morph-v3-fast" or "auto"
    },
  },
})

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Model Options

Morph provides different models optimized for different use cases:
ModelSpeedAccuracyContextBest For
morph-v3-fast4500+ tok/sec96%16k tokensQuick edits, simple changes
morph-v3-large2500+ tok/sec98%16k tokensComplex refactoring, critical code
auto2500-4500 tok/sec98%16k tokensAutomatic model selection

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Choosing a Model

providers = {
  morph = {
    model = "morph-v3-fast",  -- For speed
    -- OR
    model = "morph-v3-large", -- For accuracy
    -- OR
    model = "auto",           -- Let Morph decide
  },
}
Use morph-v3-fast for most edits. Reserve morph-v3-large for complex refactoring or production-critical code.

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Usage

Once configured, Fast Apply works automatically:

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Automatic Application

When Fast Apply is enabled, the edit_file tool is used instead of traditional tools: 
" Select code in visual mode
V5j

" Request an edit
:AvanteEdit Add type hints to function parameters
The AI:
  1. Analyzes your code
  2. Generates edit instructions
  3. Sends to Morph apply model
  4. Applies changes instantly

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Prompt Format

Fast Apply uses a specialized prompt format internally: 
<instructions>
Add type hints to function parameters
</instructions>

<code>
function process_data(items, callback)
  for i, item in ipairs(items) do
    callback(item)
  end
end
</code>

<update>
function process_data(items: table, callback: function): nil
  for i, item in ipairs(items) do
    callback(item)
  end
end
</update>
The Morph model merges the update instantly and accurately.

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Performance Comparison

ApproachAverage LatencyAccuracyCost
Traditional LLM3-10 seconds92-95%High
Fast Apply (fast)<1 second96%Medium
Fast Apply (large)<1 second98%Medium

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Configuration

Full Fast Apply configuration: 
require('avante').setup({
  behaviour = {
    enable_fastapply = true,
  },
  providers = {
    morph = {
      endpoint = "https://api.morph.so/v1",  -- Default endpoint
      model = "auto",  -- "morph-v3-fast", "morph-v3-large", or "auto"
      api_key_name = "MORPH_API_KEY",  -- Environment variable name
      timeout = 30000,  -- Request timeout in milliseconds
    },
  },
})

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Limitations

Fast Apply requires a Morph API key. It’s a paid service (though affordable for most users).
Context limit is 16k tokens (input + output combined). Very large files may need to be split.
Fast Apply is optimized for code edits, not full code generation. Use your main AI provider for generating new files.

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Troubleshooting

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API Key Issues

# Verify your API key is set
echo $MORPH_API_KEY

# If empty, add to shell config
export MORPH_API_KEY="your-key"

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Model Selection

If you’re getting inconsistent results, try explicitly setting the model: 
providers = {
  morph = {
    model = "morph-v3-large",  -- Force highest accuracy
  },
}

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Timeout Errors

Increase the timeout for large files: 
providers = {
  morph = {
    timeout = 60000,  -- 60 seconds
  },
}

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Next Steps

AI Assistance

Learn core AI features

Diff Management

Master code conflict resolution

Provider Configuration

Configure AI providers

Morph API

Get your Morph API key

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