Which has the larger context window, Claude Sonnet 5.5 and Grok 4.5?

Claude Sonnet 5.5 has the largest context window: Claude Sonnet 5.5 1,000,000 tokens and Grok 4.5 500,000 tokens.

Can I switch between Claude Sonnet 5.5 and Grok 4.5 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-sonnet-5.5, x-ai/grok-4.5).

Claude Sonnet 5.5 vs Grok 4.5

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

Claude Sonnet 5.5 Anthropicanthropic/claude-sonnet-5.5

Grok 4.5 xAIx-ai/grok-4.5

Creator

Anthropic

xAI

Released

Sep 28, 2026

Jul 8, 2026

Context window

500K

Max output

128K

500K

Input / 1MLowest provider price

$2.00

Output / 1MLowest provider price

$10.00

$6.00

Providers

IntelligenceArtificial Analysis index

56.0

38.8

CodingArtificial Analysis index

—

72.4

LatencyMedian time to first token

—

81s

ThroughputMedian tokens per second

—

<1 t/s

Accepts

Text, Image

Produces

Text

Tool calling

Yes

Structured output

Yes

Reasoning

Yes

Claude Sonnet 5.5 vs Grok 4.5: summary

Claude Sonnet 5.5 and Grok 4.5 are both available through FastRouter's OpenAI-compatible API, so switching between them is a change of model id, not a new integration.

Claude Sonnet 5.5, from Anthropic, has a 1,000,000-token context window, costs $2.00/1M input and $10.00/1M output tokens and scores 56.0 on the Artificial Analysis Intelligence Index.

Grok 4.5, from xAI, has a 500,000-token context window, costs $2.00/1M input and $6.00/1M output tokens and scores 38.8 on the Artificial Analysis Intelligence Index.

Claude Sonnet 5.5 has the largest context window and Claude Sonnet 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-sonnet-5.5", messages=[...]) # or client.chat.completions.create(model="x-ai/grok-4.5", messages=[...])

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Benchmark scores sourced from ArtificialAnalysis