Harnesses are the next frontier of vendor lock-in. LiteLLM was built to swap across model providers easily. However, as the models get saturated, the next area for competition becomes the harnesses and managed agents. To make it easy to go across vendors at the harness layer, we're launching the Lite-Harness SDK. This is a simple TypeScript+Python SDK which allows developers to change harnesses, like they change models.
It exposes harnesses in a unified Claude Agents SDK spec. This means that if you wrote your app with the Claude Agents SDK, and want to try another harness (Pi AI, Hermes, Codex, OpenCode), you can do so without rewriting your code.
Today, it supports 3 harnesses - Claude Code, Codex, and Pi AI. Please file an issue here, if you want us to add another harness.
Here's how it works:
TypeScript Example
import { query } from "@lite-harness/sdk";
const prompt = "Fix the failing test";
for await (const message of query({
prompt,
options: { harness: "claude-code", model: "claude-opus-4-8" },
})) {
console.log(message);
}
for await (const message of query({
prompt,
options: { harness: "codex", model: "gpt-5.5" },
})) {
console.log(message);
}
Python Example
from lite_harness import query, AgentOptions
prompt = "Fix the failing test"
async for message in query(
prompt=prompt,
options=AgentOptions(harness="claude-code", model="claude-opus-4-8"),
):
print(message)
async for message in query(
prompt=prompt,
options=AgentOptions(harness="codex", model="gpt-5.5"),
):
print(message)
LiteLLM AI Gateway
Lite-Harness supports proxy'ing harnesses via LiteLLM AI Gateway. This enables easy model swapping, cost controls and logging.
Point Lite-Harness at your gateway by setting two environment variables:
export LITELLM_API_BASE=https://litellm.your-company.com/v1
export LITELLM_API_KEY=sk-litellm-...
Then call as usual — every underlying model request routes through the gateway:
from lite_harness import query, AgentOptions
prompt = "Fix the failing test"
async for message in query(
prompt=prompt,
options=AgentOptions(harness="claude-code", model="claude-opus-4-8"),
):
print(message)
async for message in query(
prompt=prompt,
options=AgentOptions(harness="codex", model="gpt-5.5"),
):
print(message)
Frequently Asked Questions
Do I have to use the LiteLLM AI Gateway?
No. lite-harness works standalone — point it at provider APIs with native keys. AI Gateway integration is opt-in for teams that want central key management, budgets, fallbacks, and a single audit log across every model call.
Does swapping harnesses change agent behavior?
Yes — that's the point. Each harness keeps its native loop, tool-calling semantics, and prompt format. lite-harness unifies how you invoke them, not how they run internally. Run the same prompt across all three to see which combo lands the task best.
Is this ready for production?
lite-harness is an early, experimental project. This is in public beta. Please join our discord, to help design it to your preference.
Is this available in LiteLLM OSS?
Yes. lite-harness is MIT-licensed at github.com/LiteLLM-Labs/lite-harness. LiteLLM Enterprise adds SSO/SCIM, air-gapped deployment, 24/7 SLA, and advanced guardrails on top of the AI Gateway it pairs with.
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