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GPT-4.1 vs Claude Fable 5.1: Which AI Model Should You Choose?

Pricing, context windows, latency, capabilities, and a one-line code switch — everything you need to pick the right model.

OpenAI
Text & Chat
vs
Anthropic
Text & Chat
Verdict

Choose GPT-4.1 for cost-sensitive workloads — it is roughly 5.0× cheaper on input tokens. Choose Claude Fable 5.1 when you need its broader capabilities or stronger benchmarks.

Side-by-side specs

SpecGPT-4.1Claude Fable 5.1
ProviderOpenAIAnthropic
CategoryText & ChatText & Chat
Input cost / 1M tokens$2.40$12.00
Output cost / 1M tokens$9.60$60.00
Context window1.0M tokens1.0M tokens
Max output tokens32,768128,000
Avg. latency2.5s—
FeaturedYesYes
NewYesYes
Capabilities—
text
image

Pricing example

A typical chat workload of 100,000 input tokens plus 50,000 output tokens.

GPT-4.1
$0.72

100K in × $2.40 + 50K out × $9.60

Claude Fable 5.1
$4.20

100K in × $12.00 + 50K out × $60.00

For this workload, GPT-4.1 is cheaper than Claude Fable 5.1 by $3.48 per request.

Switch in one line

Both models live behind Railwail's OpenAI-compatible endpoint. Replace the model string and you are done.

JavaScript / TypeScript
import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.RAILWAIL_API_KEY,
  baseURL: "https://railwail.com/v1",
});

// Before — using GPT-4.1
let r = await client.chat.completions.create({
  model: "gpt-4.1",
  messages: [{ role: "user", content: "Hello" }],
});

// After — switched to Claude Fable 5.1
r = await client.chat.completions.create({
  model: "claude-fable-5-1",
  messages: [{ role: "user", content: "Hello" }],
});
Python
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["RAILWAIL_API_KEY"],
    base_url="https://railwail.com/v1",
)

# Before — using GPT-4.1
r = client.chat.completions.create(
    model="gpt-4.1",
    messages=[{"role": "user", "content": "Hello"}],
)

# After — switched to Claude Fable 5.1
r = client.chat.completions.create(
    model="claude-fable-5-1",
    messages=[{"role": "user", "content": "Hello"}],
)
cURL
# Before — using GPT-4.1
curl https://railwail.com/v1/chat/completions \
  -H "Authorization: Bearer $RAILWAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-4.1",
    "messages": [{"role": "user", "content": "Hello"}]
  }'

# After — switched to Claude Fable 5.1
curl https://railwail.com/v1/chat/completions \
  -H "Authorization: Bearer $RAILWAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-fable-5-1",
    "messages": [{"role": "user", "content": "Hello"}]
  }'

Which one wins for...

Quick verdicts derived from public specs. Always validate on your own workload.

Coding
GPT-4.1

Higher coding category match or larger context wins.

Writing
GPT-4.1

Bigger context window helps maintain long-form coherence.

Long documents
GPT-4.1

The larger context window is the deciding factor.

Vision
Claude Fable 5.1

Multimodal/vision support is required for image inputs.

Real-time chat
GPT-4.1

Lower average latency wins for interactive UX.

Cost-sensitive
GPT-4.1

The model with the lower input-token price wins.

Frequently asked questions

Which is cheaper, GPT-4.1 or Claude Fable 5.1?
GPT-4.1 is cheaper. On a 100K input + 50K output example, GPT-4.1 costs about $0.72 versus $4.20 for Claude Fable 5.1 — a saving of $3.48.
Which has more context, GPT-4.1 or Claude Fable 5.1?
GPT-4.1 and Claude Fable 5.1 have similar context windows (1.0M tokens vs 1.0M tokens).
Is GPT-4.1 better than Claude Fable 5.1 for coding?
For coding-heavy workloads we lean toward GPT-4.1 on this comparison — it scores higher on the relevant heuristics (category, tags, or context window). Both models are usable for code via Railwail's OpenAI-compatible endpoint, so the safest path is to A/B test on your own prompts.
Can I use both GPT-4.1 and Claude Fable 5.1 via Railwail?
Yes. Both GPT-4.1 and Claude Fable 5.1 are accessible through a single Railwail API key and the OpenAI-compatible /v1/chat/completions endpoint. You only change the "model" parameter to switch between them — no SDK swap, no separate billing.
How do I switch from GPT-4.1 to Claude Fable 5.1?
Replace the model identifier "gpt-4.1" with "claude-fable-5-1" in your request payload. Everything else — API key, base URL, request shape — stays the same. See the code example on this page for the exact one-line change.

Try GPT-4.1 and Claude Fable 5.1 side by side

One API key, one endpoint, both models. Start free — no credit card required.

Get Started FreeView GPT-4.1View Claude Fable 5.1