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 route 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
WeightsNot releasedNot released
CodeUnknownUnknown
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
JSON / Tool useYesYes
Structured outputsYesYes
Code executionNoYes
IDE integrationNoNo
Computer useNoNo
Parallel agentsNoNo

Benchmarks

BenchmarkClaude Sonnet 4.5GPT-5.5 Instant
MMMU Pro68.976.0

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Model pages
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Last reviewed: 2026-07-26. Data sourced from public model cards and provider documentation.