Which is cheaper, Claude Opus 5.5 and Gemini 3.8 Flash?

Gemini 3.8 Flash has the lowest input price. Per 1M input tokens: Claude Opus 5.5 from $4.00 and Gemini 3.8 Flash from $0.75.

Which has the larger context window, Claude Opus 5.5 and Gemini 3.8 Flash?

Gemini 3.8 Flash has the largest context window: Claude Opus 5.5 1,000,000 tokens and Gemini 3.8 Flash 1,048,576 tokens.

Which is smarter, Claude Opus 5.5 and Gemini 3.8 Flash?

Claude Opus 5.5 scores highest on the Artificial Analysis Intelligence Index: Claude Opus 5.5 57.6 and Gemini 3.8 Flash 40.9.

Can I switch between Claude Opus 5.5 and Gemini 3.8 Flash 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 (anthropic/claude-opus-5.5, google/gemini-3.8-flash).

Claude Opus 5.5 vs Gemini 3.8 Flash

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

Claude Opus 5.5 Anthropicanthropic/claude-opus-5.5

Gemini 3.8 Flash Googlegoogle/gemini-3.8-flash

Creator

Anthropic

Google

Released

Sep 22, 2026

Sep 2, 2026

Context window

1.05M

Max output

128K

66K

Input / 1MLowest provider price

$4.00

$0.75

Output / 1MLowest provider price

$20.00

$3.75

Providers

IntelligenceArtificial Analysis index

57.6

40.9

CodingArtificial Analysis index

—

76.3

Accepts

Text, Image, Files

Text, Image, Audio, Video, Files

Produces

Text

Tool calling

Yes

Structured output

Yes

Reasoning

Yes

Claude Opus 5.5 vs Gemini 3.8 Flash: summary

Claude Opus 5.5 and Gemini 3.8 Flash are both available through FastRouter's OpenAI-compatible API, so switching between them is a change of model id, not a new integration.

Claude Opus 5.5, from Anthropic, has a 1,000,000-token context window, costs $4.00/1M input and $20.00/1M output tokens and scores 57.6 on the Artificial Analysis Intelligence Index.

Gemini 3.8 Flash, from Google, has a 1,048,576-token context window, costs from $0.75/1M input and $3.75/1M output tokens across 2 providers and scores 40.9 on the Artificial Analysis Intelligence Index.

Gemini 3.8 Flash is the cheapest on input, 5.3× cheaper than the next model, Gemini 3.8 Flash has the largest context window and Claude Opus 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="anthropic/claude-opus-5.5", messages=[...]) # or client.chat.completions.create(model="google/gemini-3.8-flash", messages=[...])

Full API docs

Frequently asked questions

More comparisons

Benchmark scores sourced from ArtificialAnalysis