Free GPT-4 alternatives — open-source models via the OpenAI API

Correction, 2026-09-02 — pricing. An earlier version of this post said premium provider tokens are billed at the provider's rate with zero markup. That was not accurate: InferAll bills premium tokens at its own published per-token rates, which sit above the underlying provider cost. Current rates are on /pricing. The post has been corrected; nothing else about the models or the setup has changed.

GPT-4 and GPT-4o are excellent models — and at $2.50-$10/M tokens they add up fast. For developers building applications, testing ideas, or running high-volume workloads, there are genuinely capable open-source alternatives that cost $0.

All of these run on NVIDIA's DGX Cloud infrastructure (NVIDIA NIM), callable with the exact same code as OpenAI — just change two values.

---

Drop-in replacement: one base URL change

from openai import OpenAI

# Before (OpenAI)
# client = OpenAI(api_key="sk-...")

# After (free open-source models, no code changes)
client = OpenAI(
    base_url="https://api.inferall.ai/v1",
    api_key="ifu_your_key_here",  # get one at inferall.ai/keys — no card required
)

# Your existing code works unchanged
response = client.chat.completions.create(
    model="nvidia/nemotron-3-ultra-550b-a55b",  # swap in any free model
    messages=[{"role": "user", "content": "Summarize the history of the internet."}],
    max_tokens=500,
)
print(response.choices[0].message.content)

---

The best free alternatives to GPT-4

For general tasks (closest to GPT-4o):

# NVIDIA Nemotron 3 Ultra — large open model; current health probe is passing
model="nvidia/nemotron-3-ultra-550b-a55b"

# gpt-oss-20b — OpenAI's open-weight model, fast general tasks
model="openai/gpt-oss-20b"

For coding tasks (alternative to GPT-4o for code):

# GLM 5.3: general open model, good at code
model="z-ai/glm-5.3"

# Nemotron 3 Ultra: fast general model, good on code
model="nvidia/nemotron-3-ultra-550b-a55b"

For lightweight/fast tasks:

# Nemotron 3 Ultra: low-latency general/coding route
model="nvidia/nemotron-3-ultra-550b-a55b"

# gpt-oss-20b — OpenAI's open-weight model, fast on short replies
model="openai/gpt-oss-20b"

---

TypeScript / Node.js

import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.inferall.ai/v1",
  apiKey: process.env.INFERALL_API_KEY,
});

// Replace any OpenAI model with a free alternative
const response = await client.chat.completions.create({
  model: "nvidia/nemotron-3-ultra-550b-a55b",
  messages: [{ role: "user", content: "Explain quantum entanglement simply." }],
});

---

Honest tradeoffs

These models are genuinely impressive but not identical to GPT-4o:

Task	Current free NIM models	GPT-4o
General conversation	✅ Excellent	✅ Excellent
Summarization	✅ Excellent	✅ Excellent
Code generation	✅ Strong	✅ Strong
Complex multi-step reasoning	⚠️ Good	✅ Better
Instruction following	✅ Strong	✅ Strong
Context window	⚠️ Varies by model	✅ 128k
Cost	$0	$2.50-$10/M tokens

For most development, prototyping, and many production workloads, the free models are sufficient. Use GPT-4o when you specifically need its reasoning depth — InferAll routes to both from the same key. See InferAll's AI inference API for full provider and endpoint documentation.

---

Switching between models easily

The real advantage of InferAll: you can switch models without changing your integration. Test which model works best for your use case:

models_to_test = [
    "nvidia/nemotron-3-ultra-550b-a55b",
    "openai/gpt-oss-20b",
    "anthropic/claude-sonnet-4-6",  # paid — add a card for this
]

prompt = "Write a Python decorator that adds retry logic."

for model in models_to_test:
    resp = client.chat.completions.create(
        model=model,
        messages=[{"role": "user", "content": prompt}],
        max_tokens=300,
    )
    print(f"\n=== {model.split('/')[-1]} ===")
    print(resp.choices[0].message.content[:500])

---

Get started

inferall.ai/keys — sign up free and start calling (25 free NIM calls before any payment; the $5 starter pack unlocks ongoing use) at /billing. The $5 becomes spendable balance: 10+ open NIM models stay $0 in/out against it (within the free-plan daily request caps); premium providers (OpenAI, Anthropic, Google) bill at our published per-token rates.