Which is cheaper, GPT-5.5 and GPT-6 Luna?

GPT-6 Luna has the lowest input price. Per 1M input tokens: GPT-5.5 from $5.50 and GPT-6 Luna from $0.10.

Which has the larger context window, GPT-5.5 and GPT-6 Luna?

GPT-5.5 has the largest context window: GPT-5.5 1,050,000 tokens and GPT-6 Luna 400,000 tokens.

Can I switch between GPT-5.5 and GPT-6 Luna without changing my code?

Yes. All of them are served through FastRouter's OpenAI-compatible API, so switching is a change of the model parameter (openai/gpt-5.5, openai/gpt-6-luna).

GPT-5.5 vs GPT-6 Luna

Side-by-side pricing per provider, context window, benchmark scores and speed, all on one OpenAI-compatible API.

GPT-5.5 OpenAIopenai/gpt-5.5

GPT-6 Luna OpenAIopenai/gpt-6-luna

Creator

OpenAI

Released

Apr 24, 2026

Sep 22, 2026

Context window

1.05M

400K

Max output

128K

Input / 1MLowest provider price

$5.50

$0.10

Output / 1MLowest provider price

$33.00

$0.50

Providers

IntelligenceArtificial Analysis index

38.4

38.1

CodingArtificial Analysis index

74.9

—

LatencyMedian time to first token

6.1s

—

ThroughputMedian tokens per second

<1 t/s

—

Accepts

Files, Image, Text

Produces

Text

Tool calling

Yes

Structured output

Yes

Reasoning

Yes

GPT-5.5 vs GPT-6 Luna: summary

GPT-5.5 and GPT-6 Luna are both available through FastRouter's OpenAI-compatible API, so switching between them is a change of model id, not a new integration.

GPT-5.5, from OpenAI, has a 1,050,000-token context window, costs from $5.50/1M input and $33.00/1M output tokens across 2 providers and scores 38.4 on the Artificial Analysis Intelligence Index.

GPT-6 Luna, from OpenAI, has a 400,000-token context window, costs $0.10/1M input and $0.50/1M output tokens and scores 38.1 on the Artificial Analysis Intelligence Index.

GPT-6 Luna is the cheapest on input, 55× cheaper than the next model, GPT-5.5 has the largest context window and GPT-5.5 scores highest for intelligence.

Switch with one line

client = OpenAI(base_url="https://api.fastrouter.ai/api/v1", api_key="<FASTROUTER_API_KEY>") client.chat.completions.create(model="openai/gpt-5.5", messages=[...]) # or client.chat.completions.create(model="openai/gpt-6-luna", messages=[...])

Full API docs

Frequently asked questions

More comparisons

Benchmark scores sourced from ArtificialAnalysis