Finally: A Mobile App That Works With Your OpenAI & Anthropic API Keys

October 5, 2025

You've got developer accounts at OpenAI and Anthropic. You're paying per token, not monthly subscriptions. You're using the Playground or Console because they give you actual control.

But here's the problem: Both are browser-only. Try using them on your iPhone and you'll want to throw it across the room. No mobile app. No offline access. No real solution for power users who want direct API access on mobile.

Until now.

The Problem: Power Users Are Stuck With Browser Tools

If you have OpenAI or Anthropic API keys, you've probably tried:

• OpenAI Playground - Great for testing, awful for actual work on mobile
• Claude Console - Same story, browser-only, no mobile app
• ChatGPT Plus/Claude Pro - You're paying monthly subscriptions for watered-down access when you already have API keys

It's fucking ridiculous. You're a power user with direct API access, and you're stuck using tools designed for developers to test APIs, not for people who want to actually work on their phone.

Every model from OpenAI and Anthropic, right on your iPhone. Choose GPT-5, Claude Sonnet 4.5, or any other flagship model. What you pick is what you get.

What You Actually Need in a Mobile OpenAI/Anthropic API Client

Let's be clear about what matters:

1. Native iOS App (Not a Browser Wrapper)

Browser tools don't work on mobile. You need:

• Native iPhone, iPad, and Mac apps
• Offline access to conversation history
• Real mobile UI, not a desktop interface crammed into a phone

2. Direct API Access With Your Developer Keys

You already have OpenAI and Anthropic developer accounts. You shouldn't need another subscription:

• No additional subscription fees
• No middleman markup
• Direct access to the exact model you select

3. All Models Available, Not Just the "Popular" Ones

Power users need access to all models:

• GPT-5, GPT-5 Turbo, o1, o1-mini
• Claude Sonnet 4.5, Claude Sonnet 4, Claude Opus 4.1
• Older models when needed for testing or cost management
• New models the day they're released

Long-press any message to edit it. Clean up context, fix mistakes, refine prompts. ChatGPT does not let you do this. We do.

Why Consumer AI Apps Don't Cut It For API Users

ChatGPT Plus and Claude Pro charge monthly subscriptions.

But if you already have API access, you know:

• API usage typically costs $2-10/month for normal use
• You get better models via API than consumer apps
• No artificial limits on usage
• Full parameter control (temperature, max tokens, etc.)

Consumer apps are built to extract maximum subscription revenue, not give you the best AI access. If you have API keys, you're paying monthly for a worse experience than what you already have access to.

Real workspace, not a messaging app. Edit responses inline, see full context, work with AI like a document instead of a text thread.

The Solution: Cumbersome for iOS

Cumbersome is the mobile app for OpenAI and Anthropic API users. Native iOS app. Your API keys. No subscription fees.

Here's what makes it different:

Direct API Integration

Add your OpenAI and Anthropic API keys once. The app connects directly to their APIs. We're not in the middle. We don't see your conversations. We don't charge you for API usage.

Every Model, No Restrictions

• OpenAI: GPT-5, GPT-5 Turbo, o1, o1-mini, and older models
• Anthropic: Claude Sonnet 4.5, Claude Sonnet 4, Claude Opus 4.1, Claude Opus 4, all older versions

Switch models mid-conversation. Try the same prompt on multiple models. Compare responses. No limitations.

iPhone, iPad, Mac. Your conversations follow you everywhere. We never see your data. Everything syncs via your personal iCloud, not our servers. Privacy by architecture.

Features That Actually Matter for Power Users

Face/Off Mode for Maximum Quality

Want the best possible response instead of mediocre outputs? Face/Off Mode generates three responses with different creativity levels, then uses AI to pick the winner. Get quality on the first try, not after multiple manual retries.

Conversation Editing

Edit any message in the conversation history (yours or the AI's). Why does this matter?

AI conversations send the ENTIRE chat history with each message. Bad context = bad responses. Editing lets you:

• Remove off-topic tangents that confuse the AI
• Fix typos in your prompts without starting over
• Refine AI responses to improve future context
• Create conversation templates for repeated tasks

ChatGPT and Claude don't let you edit history. We do.

Full Parameter Control

• Adjust temperature, top-p, frequency penalty
• Set max tokens per response
• Custom system prompts
• View raw API responses and metadata

Not hidden behind "simple" interfaces. Full control, like the API playgrounds, but actually usable on mobile.

Real-Time Cost Tracking

See exactly what each conversation costs. Down to the fraction of a cent. No surprises.

• Token counts (input + output)
• Cost per message
• Total conversation cost
• Model pricing transparency

You're paying per token anyway. Might as well see what you're spending.

Add your OpenAI and Anthropic developer API keys. No monthly fees. No hidden costs. Pay the AI providers directly at cost.

Cross-Device Sync That Actually Respects Privacy

Your conversations sync across iPhone, iPad, and Mac via your personal iCloud account. Not our servers. We literally cannot see your data because it never passes through our infrastructure.

• API keys sync via iCloud Keychain
• Conversations sync via iCloud Documents
• Settings sync via iCloud Key-Value Store

This isn't a privacy policy promise. It's architectural. We don't have a backend database. We can't see your data even if we wanted to.

Getting Started With Your API Keys

Here's how it works:

1. Create developer accounts at OpenAI and Anthropic
2. Add a payment method to each account
3. Generate API keys in their dashboards
4. Enter keys in Cumbersome (Settings → API Keys)
5. Start using GPT-5, Claude, and other flagship models on your iPhone

The app is free. You pay OpenAI and Anthropic directly for API usage. We're completely out of the money flow.

Who This Is For

This isn't for everyone. It's for:

• Developers who want API access on mobile without building their own app
• Researchers comparing model performance across providers
• Writers who need real workspace, not chat bubbles
• Power users who understand that complexity enables capability
• Anyone who already has OpenAI/Anthropic API keys and wants to use them on iPhone

If you want AI to "just work" and don't care about technical details, stick with ChatGPT Plus. This app assumes you know what API keys are, understand token pricing, and want direct access to flagship models.

Try It Free

Cumbersome is 100% free for iPhone, iPad, and Mac.

• Use your own OpenAI and Anthropic API keys
• Pay providers directly for API usage (typically $2-10/month)
• Built for power users who want direct API access on mobile