Harness encyclopedia
The harnesses, running on a server.
TeamDay runs the agentic harnesses developers already trust — server-side, around the clock. Pick a harness per agent. Mix them on a single mission. New models from each vendor light up the moment they ship — no integration sprint.
Anthropic
Claude Code
The harness for long-horizon, verifiable engineering work.
Anthropic's official agentic coding harness. Runs the Claude family — Sonnet 4.6, Opus 4.6, Opus 4.7. Strong on multi-hour missions, tool use, and self-verification.
Models
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OpenAI
Codex
The harness for unified multimodal and computer-use missions.
OpenAI's agentic harness. Runs the GPT-5 family — including GPT-5.5 and GPT-5.5 Pro. First-class computer use, browser automation, and a unified text/image/audio/video architecture.
Models
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Gemini CLI
The harness for huge-context reasoning and Google-stack work.
Google's agentic harness. Runs the Gemini family — Gemini 3.1 Pro, Gemini 2.5 Pro. Industry-leading 2M context window and tight integration with Google Workspace, Drive, and BigQuery.
Models
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On the roadmap
Coming next
opencode
soonOpen-source, model-agnostic. Runs any LLM you point it at. Good fit for teams that want a fully open stack.
opencode.ai
Pi
soonProgrammable harness for tight, scripted workflows. Good fit when you want explicit control over each agent step.
pi.dev
Forge
soonProduction-shaped coding harness from forgecode.dev. Modeled around features, branches, and code review.
forgecode.dev
The roster grows whenever a credible new harness ships. Want yours added? Drop us a note.
Side-by-side
Capability matrix
What each harness actually ships, verified against the upstream source. Updated April 2026.
| Capability | Claude Code | Codex | Gemini CLI | opencode | Pi | Forge |
|---|---|---|---|---|---|---|
| Sub-agents | yes | yes (spawn_agent) | yes | yes | yes | yes (Forge/Sage/Muse) |
| Skills | yes | yes | yes | yes (SKILL.md) | yes | yes |
| MCP client | yes | yes (+ MCP server) | yes | yes | yes | yes |
| Hooks | rich lifecycle | notify only | richest lifecycle | rich plugin hooks | yes | event flag only |
| Slash / custom cmds | yes | yes | yes (TOML) | yes | yes | yes (:prefix) |
| Permissions / sandbox | fine-grained | OS-level (seatbelt/landlock) | Policy Engine | per-agent rulesets | gates + path protect | worktree sandbox |
| Plugins | marketplace | marketplace | extensions | plugin SDK | TS extensions | — |
| Multi-model | Anthropic + Bedrock + Vertex + Foundry | OpenAI + Bedrock + Ollama + custom | Gemini only | 12+ providers | 15+ providers | 8+ providers |
| Sessions | --resume, /branch, Remote | SQLite, ephemeral | checkpoints + git snap, /restore | LLM-summary compaction | tree-structured (branchable) | resume + :compact / :clone |
| Surfaces | CLI/VS Code/JetBrains/Desktop/Web/iOS | TUI/CLI/Web/Desktop/IDE/AppServer | TUI/VS Code/GH Actions | TUI/web/desktop/IDE | TUI/JSON/RPC/SDK | TUI/ZSH/CLI |
| Headless / SDK | Agent SDK (TS+Py) | codex exec + AppServer + SDKs | -p, JSONL, @google/gemini-cli-sdk | createOpencodeServer/Client (HTTP) | 4 modes incl. SDK | CLI only |
| License | proprietary engine | Apache 2.0 | Apache 2.0 | MIT | OSS | Apache 2.0 |
Sourced from each upstream repo (Claude Code, openai/codex, google-gemini/gemini-cli, sst/opencode, badlogic/pi-mono, antinomyhq/forge).
How harnesses fit in TeamDay
Each agent on the roster has a harness, a set of MCP servers, and a mission. The harness handles reasoning, planning, and tool calls. The MCP servers expose your data, your platforms, and visual models like Seedance 2.0 and gpt-image-2. The mission tells the agent what success looks like.