LLM Reference

Claude Sonnet 4.5 vs GPT-5.5 Instant

Claude Sonnet 4.5 (2025) and GPT-5.5 Instant (2026) are frontier reasoning models from Anthropic and OpenAI. Claude Sonnet 4.5 ships a 200k-token context window, while GPT-5.5 Instant ships a 400k-token context window. On MMMU Pro, GPT-5.5 Instant leads by 7.1 pts. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.

GPT-5.5 Instant is safer overall; choose Claude Sonnet 4.5 when reasoning depth matters.

Decision scorecard

Local evidence first
SignalClaude Sonnet 4.5GPT-5.5 Instant
Best forreasoning-heavy apps, multimodal apps, and tool-calling agentsmultimodal apps and tool-calling agents
Decision fitCoding, RAG, and AgentsCoding, RAG, and Agents
Context window200k400k
Cheapest output$15/1M tokens$30/1M tokens
Provider routes8 tracked1 tracked
Shared benchmarks1 sharedMMMU Pro leader

Decision tradeoffs

Choose Claude Sonnet 4.5 when...
  • Claude Sonnet 4.5 has the lower cheapest tracked output price at $15/1M tokens.
  • Claude Sonnet 4.5 has broader tracked provider coverage for fallback and procurement flexibility.
  • Claude Sonnet 4.5 uniquely exposes Reasoning in local model data.
  • Local decision data tags Claude Sonnet 4.5 for Coding, RAG, and Agents.
Choose GPT-5.5 Instant when...
  • GPT-5.5 Instant holds a shared-benchmark lead on MMMU Pro, ahead by 7.1 points.
  • GPT-5.5 Instant has the larger context window for long prompts, retrieval packs, or transcript analysis.
  • GPT-5.5 Instant uniquely exposes Code execution in local model data.
  • Local decision data tags GPT-5.5 Instant for Coding, RAG, and Agents.

Monthly cost at traffic

Estimate token spend from the cheapest tracked input and output route or tier on this page.

Lower estimate Claude Sonnet 4.5

Claude Sonnet 4.5

$6,150

Cheapest tracked route/tier: Microsoft Foundry

GPT-5.5 Instant

$11,500

Cheapest tracked route/tier: OpenAI API

Estimated monthly gap: $5,350. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.

Switch friction

Claude Sonnet 4.5 -> GPT-5.5 Instant
  • No overlapping tracked provider route is sourced for Claude Sonnet 4.5 and GPT-5.5 Instant; plan for SDK, billing, or endpoint changes.
  • GPT-5.5 Instant is $15/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
  • Check replacement coverage for Reasoning before moving production traffic.
  • GPT-5.5 Instant adds Code execution in local capability data.
GPT-5.5 Instant -> Claude Sonnet 4.5
  • No overlapping tracked provider route is sourced for GPT-5.5 Instant and Claude Sonnet 4.5; plan for SDK, billing, or endpoint changes.
  • Claude Sonnet 4.5 is $15/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
  • Check replacement coverage for Code execution before moving production traffic.
  • Claude Sonnet 4.5 adds Reasoning in local capability data.

Specs

Specification
Released2025-09-292026-05-05
Context window200k400k
Parameters——
ArchitectureDecoder OnlyDecoder Only
LicenseProprietaryProprietary
OpennessProprietaryProprietary
Commercial useCommercial use: conditionalCommercial use: conditional
Knowledge cutoff2025-122025-08

Pricing and availability

Pricing attributeClaude Sonnet 4.5GPT-5.5 Instant
Input price
0-200,001t
$3/1M tokens
200,001t+
$6/1M tokens
$5/1M tokens
Output price
0-200,001t
$15/1M tokens
200,001t+
$22.50/1M tokens
$30/1M tokens
Providers
Microsoft FoundryAnthropicSnowflake CortexGCP Vertex AIAWS BedrockReplicate API
OpenAI API

Capabilities

CapabilityClaude Sonnet 4.5GPT-5.5 Instant
VisionYesYes
MultimodalYesYes
ReasoningYesNo
Function callingYesYes
Tool useYesYes
Structured outputsYesYes
Code executionNoYes
IDE integrationNoNo
Computer useNoNo
Parallel agentsNoNo

Benchmarks

BenchmarkClaude Sonnet 4.5GPT-5.5 Instant
MMMU Pro68.976.0

Deep dive

On shared benchmark coverage, MMMU Pro has Claude Sonnet 4.5 at 68.9 and GPT-5.5 Instant at 76, with GPT-5.5 Instant ahead by 7.1 points. The largest visible gap is 7.1 points on MMMU Pro, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.

The capability footprint differs most on reasoning mode: Claude Sonnet 4.5 and code execution: GPT-5.5 Instant. Both models share vision, multimodal input, function calling, and tool use, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.

For cost, Claude Sonnet 4.5 lists tiered pricing: 0-200,001t is $3/1M input and $15/1M output; 200,001t+ is $6/1M input and $22.50/1M output, while GPT-5.5 Instant lists $5/1M input and $30/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Claude Sonnet 4.5 lower by about $5.90 per million blended tokens. For tiered rows, this cheapest-track view can understate interactive or fast-lane spend, so compare the tier you will actually use. Availability is 8 providers versus 1, so concentration risk also matters.

Choose Claude Sonnet 4.5 when reasoning depth, lower cheapest-tier input-token cost, and broader provider choice are central to the workload. Choose GPT-5.5 Instant when coding workflow support and larger context windows are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship.

FAQ

Which has a larger context window, Claude Sonnet 4.5 or GPT-5.5 Instant?

GPT-5.5 Instant supports 400k tokens, while Claude Sonnet 4.5 supports 200k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.

Which is cheaper, Claude Sonnet 4.5 or GPT-5.5 Instant?

Claude Sonnet 4.5 lists tiered pricing: 0-200,001t is $3/1M input and $15/1M output; 200,001t+ is $6/1M input and $22.50/1M output. GPT-5.5 Instant lists $5/1M input and $30/1M output tokens on the cheapest tracked provider. Compare the tier you will actually use; cheap async pricing can overstate savings for interactive workflows. Provider discounts or batch pricing can still change the final bill.

Is Claude Sonnet 4.5 or GPT-5.5 Instant open source?

Claude Sonnet 4.5 is listed under Proprietary. GPT-5.5 Instant is listed under Proprietary. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.

Which is better for vision, Claude Sonnet 4.5 or GPT-5.5 Instant?

Both Claude Sonnet 4.5 and GPT-5.5 Instant expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.

Which is better for multimodal input, Claude Sonnet 4.5 or GPT-5.5 Instant?

Both Claude Sonnet 4.5 and GPT-5.5 Instant expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.

Where can I run Claude Sonnet 4.5 and GPT-5.5 Instant?

Claude Sonnet 4.5 is available on Microsoft Foundry, Anthropic, Snowflake Cortex, GCP Vertex AI, and AWS Bedrock. GPT-5.5 Instant is available on OpenAI API. Provider coverage can affect latency, region availability, compliance posture, and fallback options.

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Last reviewed: 2026-06-29. Data sourced from public model cards and provider documentation.