By Sagar Shankaran, Founder of CallSphere
Sandbox, harness, code mode, and async subagents are Python-only as of April 2026. Here is the actual parity matrix and how to architect around it.
Key takeaways
TL;DR — As of April 2026, OpenAI's "next evolution" features (sandbox, harness, code mode, subagents) shipped in the Python SDK only. The TypeScript SDK has the core (agents, handoffs, guardrails, tools, sessions, tracing) and is maintained, but the new toys are Python-first with no announced TS timeline.
flowchart LR
Repo[GitHub repo] --> CI[GitHub Actions]
CI --> Eval[Agent eval suite · PromptFoo]
Eval -->|pass| Deploy[Deploy]
Eval -->|fail| Block[Block PR]
Deploy --> Prod[Production agent]
Prod --> Trace[(LangSmith trace)]
Trace --> Eval| Feature | Python | TypeScript |
|---|---|---|
| Agents, handoffs, guardrails, tools | yes | yes |
| Sessions + memory | yes | yes |
| Tracing (OpenAI dashboard) | yes | yes |
| Voice agents (Realtime) | yes | yes |
| Sandbox (managed code execution) | yes | not yet |
| Harness (declarative agent runtime) | yes | not yet |
| Code mode (model writes Python) | yes | not yet |
| Subagents (built-in delegation) | yes | "in progress" |
| MCP client + server | yes | yes |
Both SDKs share core features like agents, handoffs, guardrails, tools, human-in-the-loop, sessions, and tracing. OpenAI is working to bring code mode and subagents to TypeScript, but the company's April 2026 update was clear that the new harness and sandbox capabilities are launching first in Python, with TypeScript "planned for a future release" with no specific timeline.
Two structural reasons:
For teams shipping in 2026, this means: if your stack is TypeScript-first, you should either (a) accept that you'll be 1-2 quarters behind on net-new features, or (b) split your worker tier to a Python service for the bleeding-edge features and call it from your TS frontend.
CallSphere's voice runtime is TypeScript end-to-end (Next.js 15 App Router, Node serverless workers, OpenAI Realtime over WebRTC). Our 37 agents and 90+ tools live in TS because the voice loop demands it.
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But our batch and offline agents — GTM lead scoring, SEO content generation, affiliate-fraud detection, after-hours triage rollups — are Python. That's where we use the new harness, sandbox, and subagents features. The boundary is a Postgres-backed job table and a small RPC layer; the TS app enqueues, the Python workers execute.
This split is the same one most production teams are settling on in 2026: TS for online, Python for offline. The OpenAI Agents SDK feature gap accelerates rather than causes that pattern.
Python:
from agents import Agent, Runner, function_tool
@function_tool
def lookup_account(phone: str) -> dict:
return {"plan": "Growth", "mrr": 499}
agent = Agent(
name="Triage",
instructions="Route inbound calls.",
tools=[lookup_account],
)
result = await Runner.run(agent, "+18453884261 just called")
TypeScript:
import { Agent, run, tool } from "@openai/agents";
import { z } from "zod";
const lookupAccount = tool({
name: "lookup_account",
description: "Look up a CallSphere account by phone.",
parameters: z.object({ phone: z.string() }),
execute: async ({ phone }) => ({ plan: "Growth", mrr: 499 }),
});
const agent = new Agent({
name: "Triage",
instructions: "Route inbound calls.",
tools: [lookupAccount],
});
const result = await run(agent, "+18453884261 just called");
The shape is identical. The difference shows up only when you reach for sandbox/harness — those imports simply don't exist in JS yet.
Even with the gap, both SDKs share a strong common core:
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CallSphere ships complete AI voice agents per industry — 14 tools for healthcare, 10 agents for real estate, 4 specialists for salons. See how it actually handles a call before you book a demo.
If your project doesn't need code mode or sandbox, JS is genuinely fine. We've shipped 30+ production agents on the JS SDK and the gaps are visible only when you go looking for them.
Here's what we recommend for new builds, by team profile:
CallSphere has a demo showing this exact split if you want to see it live, and we offer pilot deployments at $149 Starter / $499 Growth / $1499 Scale with a 14-day trial.
When will TypeScript catch up? OpenAI has not given a date. April 2026 messaging used "future release" without a timeline.
Is the JS SDK going to be deprecated? No. It's actively maintained, the Realtime voice path is JS-first, and the core agent surface ships features in both languages.
Can I use the Python SDK from a Next.js app? Not directly. Stand up a Python service and call it.
Should I rewrite my JS agent in Python? Almost never. Wrap the Python service instead.
Written by
Sagar Shankaran· Founder, CallSphere
Sagar Shankaran is the founder of CallSphere, where he builds production AI voice and chat agents deployed across healthcare, hospitality, real estate, and home services. He writes about agentic AI, LLM engineering, and shipping voice agents that handle real calls in production.
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