Aider is the original open-source AI pair programmer - terminal-only, Apache 2.0, BYOK over litellm. If you're looking for an alternative it's usually because you don't want to manage Anthropic + OpenAI + Google API keys, you don't want to watch multiple provider dashboards, you want native MCP without community plugins, or you want a free tier without bringing keys. This page covers cto CLI - a CLI that ships as an opencode plugin + provider, so the agent runs in your terminal but the LLM calls route through a managed gateway - and the broader alternatives if cto isn't the right fit.
TL;DR. cto CLI is the closest "Aider but no provider keys, free" swap. It's an opencode plugin + provider - the agent loop, file editing, plan mode, worktrees, hooks, skills, slash commands, and native MCP are all opencode (Apache 2.0); cto adds the cto.new gateway so you don't bring keys. Pick from 10+ frontier LLMs via opencode's /model slash command (Opus 4.8, GPT-5.5, Gemini 3.1 Pro, GPT-5.3 Codex, and more). Free forever, ad-supported, rolling 24h+7d limits. If you specifically want to stay BYOK with direct provider connections, Aider is still the right tool - this page is for the cases where you'd rather not.
What you stop dealing with on cto CLI
If you've been using Aider, this is the practical day-to-day difference:
| Aider | cto CLI |
|---|---|
| You sign up for Anthropic, OpenAI, Google, OpenRouter accounts | You sign in to cto.new with email or GitHub |
| You generate + rotate API keys per provider | No keys |
| You watch each provider's usage dashboard + bill | One rolling 24h+7d window, no bill on free |
| You pick the model via litellm config | Pick the model via opencode's /model |
| You configure MCP via community wrappers | Native MCP, account-wide config |
Aider's BYOK model is genuinely powerful - full control, direct provider connections, anything litellm supports. The trade is operational overhead. cto CLI moves that overhead to the gateway.
What cto CLI is
Install:
curl -fsSL https://cto.new/install | bash
cto ships as an opencode plugin + provider. The agent loop, file editing, plan mode, worktrees, hooks, skills, slash commands, LSP, and native MCP - all opencode (Apache 2.0), running locally in your terminal. cto's plugin adds the install/auth/upgrade layer and the ads layer; cto's provider is the cto.new gateway that handles LLM calls so you don't bring keys. You pick a model from the frontier menu via opencode's /model slash command.
Inside the TUI, /cto-login and /cto-logout let you re-auth without quitting. Sub-commands the wrapper doesn't recognize pass through to opencode.
The model menu
The cto.new gateway exposes Claude Opus 4.8 + Sonnet 4.6, GPT-5.5, GPT-5.3 Codex, Gemini 3.5 Flash + 3.1 Pro, GLM 5.1, Grok 4.20, Kimi K2.6, MiniMax M2.7. Pick whichever you want via opencode's /model slash command - the cto.new gateway handles provider auth so you don't bring keys.
Aider users will recognize the manual control pattern. The difference: you pick from a managed gateway menu instead of wiring litellm against your own keys.
MCP without the community-plugin layer
Aider's MCP support is inverted: there's no native client, but community projects like aider-mcp-server expose Aider's tools to MCP clients (Claude Desktop, Cursor IDE). That's useful but it's the inverse of what most CLIs mean by "MCP support" - agents calling external tools.
cto CLI has the standard direction via opencode's native MCP client. Configure your MCP servers in opencode's standard MCP config (stdio or streamable HTTP) and the agent picks them up. Whatever MCP server you want - Linear, Sentry, Notion, your own custom server - works the same way it would in vanilla opencode.
Pricing trade
Aider's CLI is free; provider costs are whatever you negotiate with Anthropic / OpenAI / Google / etc. If you're a heavy user, that adds up - typical solo developer on a Claude + OpenAI stack runs $50–$200/month in provider bills.
cto CLI is free forever on a rolling 24h + 7d window. Heavy users hit the window and either wait or upgrade to premium (raised limits, premium models). No per-token meter.
The arithmetic: if you'd otherwise be paying $50+/month in BYOK token costs, cto's free tier likely covers most of your usage without a bill. If you're a very heavy user, you'll bump the cap and the question becomes whether cto's premium is cheaper than your provider bills (it usually is).
When to stay on Aider
This is honest - Aider is still right for some cases:
- You want direct provider connections. You don't want the cto.new gateway sitting between you and Anthropic / OpenAI / Google; you'd rather pay providers directly.
- You're benchmarking models that aren't in cto's gateway. Aider via
litellmreaches every model anyone has ever wired. cto has 10+, but the catalog is curated. - You're running fully offline / on a local model. Aider with Ollama is mature. cto CLI requires the cto.new gateway, so it needs internet.
- You prefer open-source end-to-end. Aider is Apache 2.0; cto CLI is a proprietary wrapper around open-source opencode.
If none of these apply, cto CLI is the operational simplification.
Other CLIs in the same space
If neither Aider nor cto CLI fits:
- Claude Code - best Anthropic-native UX. Paid only.
- Cursor CLI - best frontier-model menu for Cursor editor users. Tied to Cursor's $20/mo Pro plan.
- GitHub Copilot CLI - best GitHub Actions integration. AI Credits billing from June 2026.
- Codex CLI - OpenAI's open-source terminal agent (Apache 2.0, Rust).
- Gemini CLI - generous bare-account free tier (1,000 req/day with a Google account).
FAQ
Is Aider free?
The Aider CLI itself is free and open-source (Apache 2.0). You pay providers directly per token. Free as in software cost, not free as in usage.
Does cto CLI require API keys?
No. The cto.new gateway handles provider auth. You sign in to cto with email or GitHub; the CLI inherits your account.
What's the relationship between cto CLI and opencode?
cto CLI ships as an opencode plugin + provider. opencode is the open-source TUI coding agent (Apache 2.0); cto's plugin layer adds the cto-specific auth/install/upgrade behavior and the ads layer; cto's provider is the cto.new gateway that handles LLM calls so you don't bring keys. Sub-commands cto doesn't recognize pass through to opencode.
Can I use cto CLI offline?
No - cto CLI requires the cto.new gateway. If you need offline, Aider with a local model (Ollama, vLLM) is the path.
Does cto CLI support local models?
Indirectly - via OpenRouter or compatible providers in the gateway. Native local-model support isn't a current feature. Aider is stronger here.
Can I migrate Aider's .aider.conf.yml to cto CLI?
There's no direct conversion. cto CLI's config is account-bound at cto.new (settings, MCP servers, default model preferences) rather than per-project YAML. Project-specific instructions can go in a project README or opencode-style rules file that the agent reads.