How to Use Claude Opus 4.5 API Free with OpenCode (2026)

Claude Opus 4.5 is Anthropic's most advanced language model, known for its exceptional reasoning, coding, and creative writing capabilities. However, API access costs $15 per million input tokens and $75 per million output tokens -- making it one of the most expensive models to use at scale.

OpenCode is an open-source terminal-based AI coding assistant that supports multiple LLM providers. Combined with free API credits and smart configuration, you can use Claude Opus 4.5 without spending money. This guide shows you exactly how.

What Is OpenCode?

OpenCode is an open-source, terminal-native AI coding assistant similar to Claude Code and Codex CLI. Key features include:

Works in your terminal with any project
Supports multiple LLM providers (Anthropic, OpenAI, Google, local models)
Agentic coding with file editing, code execution, and shell commands
LSP integration for intelligent code understanding
Conversation history and session management
Fully open source (MIT license)

Feature	OpenCode	Claude Code	Codex CLI
Open source	Yes	No	Yes
Claude support	Yes	Yes (native)	No
Multi-provider	Yes	No (Anthropic only)	No (OpenAI only)
Free to use	Yes (BYOK)	No	Limited free
File editing	Yes	Yes	Yes
Code execution	Yes	Yes	Yes
LSP integration	Yes	Limited	No

Step 1: Get Free Claude API Credits

Before setting up OpenCode, you need API access to Claude. Here are the ways to get free credits:

Method 1: Anthropic Free Trial Credits

New Anthropic API accounts receive $5 in free credits:

Go to console.anthropic.com
Create a new account
Navigate to API Keys and generate a key
You automatically receive $5 in credits (valid for 30 days)

At Claude Opus 4.5 pricing, $5 gives you approximately:

~333K input tokens (about 250 pages of code)
~66K output tokens (about 50 pages of generated code)

Method 2: Anthropic Developer Programs

Anthropic runs developer programs that provide extended free credits:

Anthropic Build Program: Up to $1,000 in credits for startups and indie developers
Academic Research Program: Free credits for university researchers
Open Source Maintainer Program: Credits for open-source project maintainers

Apply at anthropic.com/programs with a description of your project.

Method 3: Third-Party Providers with Free Tiers

Several API providers offer Claude access with their own free tiers:

Provider	Free Credits	Claude Models Available	Notes
Amazon Bedrock	$300 AWS free tier	Claude Opus 4.5, Sonnet	Requires AWS account
Google Cloud Vertex	$300 free credits	Claude Opus 4.5, Sonnet	Requires GCP account
OpenRouter	$1 free credit	All Claude models	Easy setup

Amazon Bedrock is the most generous option. New AWS accounts get $300 in free tier credits that can be applied to Claude API calls.

Method 4: Use OpenRouter Free Models + Claude

OpenRouter lets you mix free models with paid Claude access. Use free models for routine tasks and save Claude Opus 4.5 for complex problems:

# Get an OpenRouter API key at openrouter.ai
# Free models available: Gemini Flash, Llama, Mistral

Step 2: Install OpenCode

Using Go Install

# Requires Go 1.22+
go install github.com/opencode-ai/opencode@latest

Using Homebrew

brew install opencode

Using the Install Script

# macOS/Linux
curl -fsSL https://opencode.ai/install.sh | sh

# Verify installation
opencode --version

Building from Source

git clone https://github.com/opencode-ai/opencode.git
cd opencode
go build -o opencode .
sudo mv opencode /usr/local/bin/

Step 3: Configure OpenCode for Claude Opus 4.5

Create a configuration file at ~/.config/opencode/config.json:

{
  "provider": "anthropic",
  "model": "claude-opus-4-5-20250514",
  "apiKey": "sk-ant-your-api-key-here",
  "maxTokens": 8192,
  "temperature": 0.7,
  "systemPrompt": "You are an expert software engineer. Write clean, well-tested code with proper error handling."
}

Using Environment Variables

# Add to your shell profile (~/.zshrc or ~/.bashrc)
export ANTHROPIC_API_KEY="sk-ant-your-api-key-here"
export OPENCODE_MODEL="claude-opus-4-5-20250514"

Using Amazon Bedrock (for AWS Free Tier)

{
  "provider": "bedrock",
  "model": "anthropic.claude-opus-4-5-20250514-v1:0",
  "region": "us-east-1",
  "profile": "default"
}

Make sure your AWS credentials are configured:

aws configure
# Enter your AWS Access Key, Secret Key, and region

Using OpenRouter

{
  "provider": "openrouter",
  "model": "anthropic/claude-opus-4-5",
  "apiKey": "sk-or-your-key-here",
  "baseUrl": "https://openrouter.ai/api/v1"
}

Step 4: Using OpenCode with Claude Opus 4.5

Interactive Mode

# Start OpenCode in your project directory
cd ~/projects/my-app
opencode

# You will see a terminal UI where you can chat and give tasks
> Analyze this project and suggest architectural improvements

Direct Commands

# Ask a question
opencode ask "How do I implement WebSocket authentication in Node.js?"

# Edit files
opencode edit "Add rate limiting middleware to src/server.ts"

# Run a complex task
opencode task "Refactor the database layer to use the repository pattern"

# Review code
opencode review src/auth/

Practical Examples

Generate a complete API endpoint:

opencode task "Create a new REST endpoint POST /api/v1/webhooks that:
1. Validates the webhook payload using Zod
2. Stores the webhook in PostgreSQL
3. Queues an async job to process it
4. Returns a 202 Accepted response
Follow the existing patterns in src/routes/"

Debug a failing test:

opencode task "The test in tests/auth.test.ts is failing with
'Expected 401 but received 200'. Investigate why and fix it."

Explain and document code:

opencode ask "Explain what the function processTransaction in src/billing/processor.ts
does step by step, and add JSDoc documentation to it"

Step 5: Maximize Your Free Credits

Claude Opus 4.5 is expensive, so every token matters when using free credits. Here are strategies to stretch your budget:

Use a Dual-Model Setup

Configure OpenCode to use a cheaper model by default and switch to Opus 4.5 only when needed:

{
  "provider": "anthropic",
  "model": "claude-sonnet-4-20250514",
  "apiKey": "sk-ant-your-key-here",
  "models": {
    "default": "claude-sonnet-4-20250514",
    "complex": "claude-opus-4-5-20250514"
  }
}

# Use Sonnet for routine tasks (5x cheaper)
opencode task "Format this code and add type annotations"

# Switch to Opus for complex reasoning
opencode --model complex task "Design a distributed caching strategy for this microservice"

Minimize Context Size

# Bad: sends entire project context
opencode task "Fix the bug"

# Good: targeted context saves tokens
opencode task "Fix the null pointer error in src/utils/parser.ts line 87.
The input can be undefined when the API returns an empty response."

Track Your Token Usage

# Check usage in OpenCode
opencode usage

# Or check directly in the Anthropic console
# https://console.anthropic.com/usage

Estimated Token Costs for Common Tasks

Task Type	Avg Input Tokens	Avg Output Tokens	Cost (Opus 4.5)
Quick question	500	1,000	~$0.08
Code review (1 file)	3,000	2,000	~$0.20
Bug fix (targeted)	5,000	3,000	~$0.30
Feature implementation	10,000	5,000	~$0.53
Full refactoring	20,000	10,000	~$1.05

With $5 in free credits, you can perform approximately 10-15 substantial coding tasks or 50+ quick questions with Claude Opus 4.5.

Troubleshooting

"Invalid API Key" Error

# Verify your key is set correctly
echo $ANTHROPIC_API_KEY

# Test the key directly
curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "content-type: application/json" \
  -H "anthropic-version: 2024-01-01" \
  -d '{"model":"claude-sonnet-4-20250514","max_tokens":100,"messages":[{"role":"user","content":"Hi"}]}'

"Insufficient Credits" Error

Your free credits may have expired (typically 30 days). Options:

Create a new Anthropic account with a different email
Switch to Amazon Bedrock or Google Cloud Vertex for their free tier credits
Use a cheaper model like Claude Sonnet 4

Slow Responses

Claude Opus 4.5 is inherently slower than Sonnet due to its larger size. For faster responses:

{
  "maxTokens": 4096,
  "temperature": 0.3
}

Lower maxTokens and temperature reduce generation time.

Frequently Asked Questions

Is this actually free? Yes, with limitations. New Anthropic accounts get $5 in free credits. AWS and GCP free tiers provide additional credits. After credits expire, you need to pay or create a new account.

How does OpenCode compare to Claude Code? OpenCode is open-source and supports multiple providers, while Claude Code is Anthropic's official tool that only works with Claude models. Claude Code has tighter integration with Anthropic's API but costs money to use.

Can I use Opus 4.5 in Cursor or Windsurf? Yes, you can add your Anthropic API key to Cursor or Windsurf settings. However, OpenCode lets you use it from the terminal with lower overhead.

Is there a completely free way to get Opus-level quality? The closest free alternatives are Gemini 2.5 Pro (free API tier from Google) and DeepSeek V3 (open source). Neither fully matches Opus 4.5, but they are competitive for most coding tasks.

Wrapping Up

Using Claude Opus 4.5 for free is possible through a combination of trial credits, cloud provider free tiers, and smart token management. OpenCode is the best open-source tool for the job because it gives you full control over which model and provider you use, with no subscription fees.

Start by claiming your $5 in Anthropic credits, install OpenCode, and focus your Opus 4.5 usage on the complex tasks where it truly outperforms cheaper models. For everything else, Claude Sonnet 4 or Gemini Flash will get the job done at a fraction of the cost.

If you are building applications that need AI-generated media, Hypereal AI offers pay-as-you-go API access to video generation, AI avatars, and image creation. Start with 35 free credits -- no API key juggling required.