Choosing Your Coding Agent

CodeMantis supports two coding agent CLIs as first-class options: Claude Code and OpenAI Codex. You only need one installed to use the app, but having both unlocks per-task routing and lets you split workloads (and your subscription pool) across two vendors.

This page is a short decision guide.

The Short Version

Both, ideally. When both CLIs are installed and signed in, CodeMantis grows an Agent Picker in the Project Picker and a per-task routing table in Settings › Agents. You don't have to pick a side — you can split your work.

How They Differ Inside CodeMantis

The chat panel, activity feed, file viewer, terminals, SpecWriter, Implementation Guide, Self-Drive, MCP management, project templates, preview browser, and Multi-AI Assistants all work the same way regardless of which agent powers your session. Two things change:

1. The input toolbar. Claude Code sessions show the Mode Selector (Normal, Auto-Accept, Plan, Auto, Don't Ask, Bypass). Codex sessions show the Codex Policy Pill (sandbox: read-only / workspace-write / danger × approval-policy: untrusted / on-request / on-failure / never). Different model, same goal: control how much autonomy your agent has.
2. Authentication. Claude Code uses claude login (OAuth against your Anthropic account). Codex uses codex login (OAuth against your OpenAI account, credentials in ~/.codex/auth.json). Both are persisted between launches.

Per-Task Routing (v1.5.0)

Settings › Agents shows a Per-task Defaults table when both CLIs are installed and signed in. Categories:

• main_chat — the agent your main project sessions default to
• spec_writer — the agent SpecWriter hands off to when you click Implement
• assistant — the agent powering local-CLI assistant tabs in the right panel
• help — the agent powering the in-app Help assistant

Each row is a dropdown. Pick a specific agent, or leave it on "Use primary" to follow whichever agent you've made the default. The setting is persisted as a sparse map (defaultAgentByTask in settings).

A 7-day usage-split card at the bottom of the tab breaks down tokens and estimated cost per agent so you can see where your subscription pool actually goes.

Self-Drive is not a task category. Self-Drive always inherits the agent of the session it attaches to. If main_chat is routed to Codex, Self-Drive runs on Codex too. This is deliberate — Self-Drive's evidence vocabulary is calibrated per agent and mixing agents inside a single autonomous run would mean reasoning across two grammars.

A Worked Example

A common configuration:

• main_chat → Codex (cheaper subscription headroom for hot iterations on ChatGPT Pro)
• spec_writer → Claude Code (strong long-form spec reasoning)
• assistant → Use primary (follows your default)
• help → Use primary

You write a spec with SpecWriter; it routes to Claude; the spec is excellent. You click Implement and the resulting sessions land back on your main_chat agent, Codex, where you have plenty of headroom for the actual coding work. Self-Drive picks up Codex from the session and runs autonomously. The 7-day usage card shows the split so you can rebalance if either pool drains faster than expected.

Why CodeMantis Supports Both

Short version: CodeMantis is the interface, not the agent. The agent you bring is yours. We built the AgentAdapter abstraction in v1.2.0 so future CLIs are a config away, not a rewrite. v1.3.0 added Codex; v1.5.0 added per-task routing.

For the long version — including the Anthropic June 15, 2026 licensing change that made vendor optionality non-negotiable — see the blog post: Why CodeMantis Now Supports Two Coding Agents (and Soon More).

Next Steps

• Installing Claude Code — Set up the Anthropic CLI.
• Installing Codex — Set up the OpenAI CLI.
• Per-task agent routing — Full reference for the Settings › Agents tab.
• Session Modes Explained — Claude Code's mode model and Codex's policy model side by side.