Opus 5.5 vs GPT-5.5 Pro: $4 vs $30 Pricing Compared

Published September 23, 2026 - San Francisco, California. Claude Opus 5.5 launched September 22, 2026 at $4 per million input tokens. GPT-5.5 Pro launched April 23, 2026 at $30 per million input tokens.

Opus 5.5 is the newer premium Anthropic flagship with adaptive thinking always on; GPT-5.5 Pro is the established OpenAI max-effort tier with slower but more thorough responses. The pricing gap is roughly 7.5x on input and 9x on output (Anthropic, September 2026; OpenAI API docs, April 2026).

At a glance

• Opus 5.5: $4 input / $20 output per million tokens; 1M context; cache reads $0.20.
• GPT-5.5 Pro: $30 input / $180 output per million tokens; 1.05M context; no cache discount.
• Opus 5.5 is 7.5x cheaper input, 9x cheaper output than GPT-5.5 Pro.
• Opus 5.5 launched Sep 22, 2026; GPT-5.5 Pro launched Apr 23, 2026.
• Opus 5.5 fast mode: up to 2.5x speed via Claude Code.
• GPT-5.5 Pro: some requests take minutes; max-effort design.
• Opus 5.5: Anthropic API, Bedrock, Vertex AI, Claude Code.
• GPT-5.5 Pro: OpenAI Responses API + Batch, ChatGPT Pro/Business/Enterprise.

Data last verified September 23, 2026 from Anthropic's announcement and API documentation, OpenAI's GPT-5.5 Pro model card, and the Claude pricing page.

Quick Answer

Claude Opus 5.5 is cheaper, faster on the fast mode, and more widely available; GPT-5.5 Pro is older, slower by design, and produces the most thorough responses on the hardest reasoning tasks.

The pricing gap is roughly 7.5x on input and 9x on output (Anthropic, September 2026; OpenAI API docs, April 2026).

For most agentic coding, document analysis, and tool-using workflows, Opus 5.5 matches GPT-5.5 Pro's quality at far lower cost. For research tasks where the answer correctness justifies a $30 input cost, GPT-5.5 Pro still leads on the hardest problems.

Pricing at a glance

Both models publish standard direct API rates in US dollars per million tokens:

Source: Anthropic pricing page (September 2026), OpenAI API docs (April 2026).

The cached-input pricing only applies to Opus 5.5. Anthropic also publishes 5-minute and 1-hour cache writes at $5 and $8 per million tokens respectively. GPT-5.5 Pro has no cache-discount tier (Anthropic pricing, September 2026).

Context windows

Opus 5.5 ships a 1,000,000-token context window with a 128,000-token standard output limit. GPT-5.5 Pro ships a slightly larger 1,050,000-token context window with the same 128K max output. The difference is marginal; both handle million-token codebases and long-document analysis (Anthropic API, September 2026; OpenAI API docs, April 2026).

On real-world long-context benchmarks, Opus 5.5's 1M context is reliable up to roughly 800K tokens for recall-heavy tasks. GPT-5.5 Pro's 1.05M context has similar recall behaviour. Both are at the frontier of usable long-context for the September 2026 timeframe.

Reasoning and effort controls

Opus 5.5 ships with adaptive thinking always on and a default reasoning effort of medium. Users can adjust per request via Anthropic API or Claude Code. The default effort changes the cost and latency of every response (Anthropic, September 2026).

GPT-5.5 Pro ships with explicit reasoning effort selection per request: medium, high, or xhigh. High is the default. The model uses more compute by design and some requests take minutes rather than seconds for the most thorough reasoning paths (OpenAI API docs, April 2026).

The two models occupy different positions on the cost-quality frontier. Opus 5.5 is positioned for everyday agentic work where adaptive thinking at moderate effort produces consistent results at low per-token cost. GPT-5.5 Pro is positioned for max-effort research where the answer correctness justifies the price premium.

Speed and latency

Opus 5.5 ships a fast mode at up to 2.5x speed via Claude Code and the Anthropic Platform. The fast mode applies to the standard output tier and requires explicit selection per request (Anthropic, September 2026).

GPT-5.5 Pro does not offer a fast mode. The model's positioning is thorough reasoning over raw latency. Production deployments typically use GPT-5.5 Pro for background research tasks or batch jobs where the multi-minute response is acceptable.

For interactive coding or chat where response latency matters, Opus 5.5 fast mode is closer to GPT-5.6 Sol than to GPT-5.5 Pro. For batch research where the answer quality matters more than when it arrives, GPT-5.5 Pro wins on the difficulty axis.

Where each model wins

Three workloads side-by-side:

• Agentic coding: Opus 5.5 at adaptive medium is competitive with GPT-5.5 Pro at high effort on Terminal-Bench 2.0 and SWE-bench-style scenarios. The cost gap is large; Opus 5.5 wins on price-performance for everyday agent work.
• Deep research: GPT-5.5 Pro at xhigh produces more thorough output on multi-document synthesis, factual accuracy, and long-horizon reasoning chains. The cost is justified when the research outcome is high-value.
• Long-context recall: Both models handle 800K+ token contexts effectively. On terminal-coder recall (search within million-token codebases), GPT-5.5 Pro tests slightly higher; Opus 5.5 follows closely.

For most workloads, Opus 5.5 is the better default - it is cheap, fast, available on the Anthropic API plus Bedrock and Vertex AI, and produces Opus 5.1-tier results. Reach for GPT-5.5 Pro when the question is hard enough that cost-per-answer matters less than answer quality.

Where to access each

Opus 5.5 ships on the Anthropic API (Claude Platform), Amazon Bedrock, Google Vertex AI, and Claude Code 2.1.280+. Third-party model routers can bill at provider cost. API model ID is `claude-opus-5-5` (Anthropic API, September 2026).

GPT-5.5 Pro ships only on OpenAI's Responses API and Batch API - not the Chat Completions endpoint. Default snapshot is `gpt-5.5-pro-2026-04-23`. The model is also available through ChatGPT Pro, Business, and Enterprise plans (OpenAI API docs, April 2026).

For Chat Completions endpoint users, GPT-5.5 Pro is the redirect target when a request exceeds the limit of GPT-5.6 Sol or GPT-6 Sol. For Responses API users, GPT-5.5 Pro is the explicit reasoning-effort selection.

Common alternatives to consider

Two recent models overlap with both Opus 5.5 and GPT-5.5 Pro at lower cost:

• OpenAI GPT-6 Sol (Sep 22, 2026): $5 input, $30 output, 1.05M context. Same $5/$30 tier as Opus 5.5 but with cheaper cached input at $0.20 per million. Best for new agentic-coding workflows.
• Anthropic Claude Fable 5.1 (Sep 1, 2026): $10 input, $50 output, 1M context. Anthropic's top tier above Opus 5.5; for the hardest research questions where cost is secondary.

Models at the other end - GPT-6 Luna, Claude Haiku 4.5, and Grok 4.7 - are cheaper and faster but lower-capability substitutes for everyday high-volume work.

What to do today

Three actions for the September 23 decision window:

• If you were using Opus 5 (the prior tier), migrate to Opus 5.5 by changing the model id to `claude-opus-5-5`. Pricing drops 40%; behaviour is largely the same with adaptive thinking now on by default.
• If you were using GPT-5.5 Pro for everyday coding, route the same traffic to Opus 5.5 at roughly 7.5x cost savings and accept Opus 5.5's adaptive thinking as the new default reasoning strategy.
• If you are choosing between the two models for a new deployment, start with Opus 5.5 fast mode for interactive work and add GPT-5.5 Pro for explicit max-effort research where the cost is justified.

The Anthropic migration guide for Opus 5.4 → Opus 5.5 is published on docs.anthropic.com; the change is non-breaking for most workloads.

Frequently Asked Questions

Is Opus 5.5 better than GPT-5.5 Pro for coding?

On price-performance, Opus 5.5 wins for everyday agentic coding - you get within a few points of GPT-5.5 Pro on Terminal-Bench 2.0 at less than 15% of the per-token cost.

On raw accuracy at the very hardest coding benchmarks, GPT-5.5 Pro at xhigh still leads (Anthropic, September 2026; OpenAI, April 2026).

Does Opus 5.5 have cached input pricing?

Yes - cached input reads on Opus 5.5 cost $0.20 per million tokens, 5% of the standard $4 input rate.

GPT-5.5 Pro does not have a cached-input discount tier. For workflows that benefit from prompt caching, the Opus 5.5 effective price drops further than the headline 7.5x gap (Anthropic pricing, September 2026).

Can I use the OpenAI Chat Completions endpoint with GPT-5.5 Pro?

No - GPT-5.5 Pro only ships on the OpenAI Responses API and Batch API.

The Chat Completions endpoint serves GPT-5.5 (non-Pro) and the GPT-6 series. Customers needing the Chat Completions interface with max-effort reasoning should use GPT-6 Sol at the same $5/$30 tier as a substitute (OpenAI API docs, April 2026).

Which model has the better knowledge cutoff?

Opus 5.5 inherits Claude's 2026 training scope. Anthropic publishes model cards with the cutoff at training time.

GPT-5.5 Pro was trained with a December 1, 2025 cutoff per the OpenAI API docs - five months older than the typical Anthropic cutoff for Opus-class models. For time-sensitive factual tasks, Opus 5.5 has the newer knowledge base (OpenAI API docs, April 2026; Anthropic, September 2026).

Does Opus 5.5 support voice input?

No - Opus 5.5 is text-in / text-out like most frontier LLMs. For voice workflows, both Anthropic and OpenAI ship voice-specific models. Anthropic routes through Claude's SDK; OpenAI offers the Realtime API for low-latency voice. The frontier text models are unrelated (Anthropic, September 2026).

Is GPT-5.5 Pro being deprecated?

Not as of September 2026 - GPT-5.5 Pro remains OpenAI's established max-effort tier.

The GPT-6 series (Astra, Sol, Luna) sits one tier lower in pricing and one tier newer in training. For workloads where GPT-5.5 Pro's reasoning profile is the established fixture, the model continues to ship (OpenAI API docs, April 2026; aireleasetracker.com, September 2026).