GPT-5.5 vs Claude Opus 4.7 vs Gemini 3.1 Pro (May 2026)

The April 2026 model wave is settled, and the picture is more interesting than the headlines. OpenAI shipped GPT-5.5 in April with a major Codex upgrade. Anthropic shipped Claude Opus 4.7 the same week. Google’s Gemini 3.1 Pro had landed in March. By May 1, 2026, three weeks of real-world testing makes the actual split clear — and it isn’t what most major outlets reported.

Last verified: May 1, 2026

The headline split

• Claude Opus 4.7 wins on coding, careful reasoning, hallucination rate, and long-context retrieval.
• GPT-5.5 wins on autonomous agent tasks, computer use, tool orchestration in long pipelines, and absolute Terminal-Bench 2.0.
• Gemini 3.1 Pro wins on multimodal (especially video and image-heavy reasoning), long-form research synthesis, and price for context-heavy workloads.

It’s a 6-4 split benchmark-by-benchmark on capability, with OpenAI winning the harness-and-tools layer and Anthropic winning the model layer. Outlets that report a single overall winner are either summing benchmarks the writer thinks matter or quoting the vendor.

The benchmark numbers

Benchmark	Opus 4.7	GPT-5.5	Gemini 3.1 Pro
SWE-bench Verified	87.6%	~75%	~72%
Terminal-Bench 2.0 (model)	69.4%	82.7% (with Codex harness)	68.5%
Graphwalks BFS 256k	wins	second	third
Graphwalks parents 256k	wins	second	third
Graphwalks parents 1M	wins	second	third
GDPval (research workflows)	54.7%	52.2%	51.4%
ECI (Epoch Capabilities Index)	second	first (GPT-5.4 Pro tops)	third
Hallucination rate (Artificial Analysis)	lowest	medium	medium
Computer use / autonomous agent tasks	second	best	third
Multimodal video reasoning	third	second	best

Reading this table: Opus 4.7 has more first-place finishes on capability benchmarks. GPT-5.5 has more first-place finishes on agentic and tool-orchestration benchmarks. Gemini 3.1 Pro is the multimodal winner.

Why the headlines say “GPT-5.5 wins”

Two reasons. First, OpenAI marketed GPT-5.5 around “AI you can delegate to,” which framed reviews around agentic delegation tasks — a category GPT-5.5 actually wins. Second, the Terminal-Bench 2.0 number reviewers cite for GPT-5.5 (82.7%) is the harness score running GPT-5.5 inside the Codex CLI, not the bare model score. The bare model lands closer to 75% on Terminal-Bench 2.0; the Codex harness is where the extra ~8 points come from. That’s still a real win, but it’s a Codex win, not a model win.

When Opus 4.7 runs inside Claude Code with the equivalent harness, the gap narrows. On the bare model side of Terminal-Bench 2.0, Opus 4.7 leads.

Where each model genuinely wins

Claude Opus 4.7 — the careful reasoning model

Best for:

• Production-grade coding (highest SWE-bench Verified score in May 2026).
• Long documents, large codebases, deep research synthesis where retrieval accuracy matters.
• Anything trust-sensitive — legal, medical, financial — because of the lowest measured hallucination rate.
• Working inside Claude Code on real engineering work.

Pricing: Claude Pro $20/mo, Claude Max $100/mo; API $15/$75 per million input/output tokens.

GPT-5.5 — the agent model

Best for:

• Computer use — Codex CLI, Codex Cloud, OpenAI Operator-style automation.
• Long autonomous pipelines (instruction persistence over many steps was the headline GPT-5.5 improvement).
• Multi-tool orchestration where the model has to chain calls reliably.
• ChatGPT-native workflows — voice mode, custom GPTs, the broader OpenAI ecosystem.

Pricing: ChatGPT Plus $20/mo, Pro $200/mo; API competitive with Anthropic’s, slightly cheaper on input.

Gemini 3.1 Pro — the multimodal model

Best for:

• Video understanding and long-form video reasoning (the only one of the three with native multi-hour video context).
• Long-form research synthesis where you’re feeding 500k+ tokens.
• Image-heavy workflows and Google Workspace integrations.
• Cost — Gemini 3.1 Pro is the cheapest on long-context tokens.

Pricing: Google AI Pro $20/mo; Ultra plan with extended Gemini 3.1 Pro at $250/mo; very competitive per-token API pricing.

What changed in late April 2026

Three things shifted the picture in the last two weeks:

1. Anthropic shipped Opus 4.7 mid-April with major gains on GDPval (research workflows) and hallucination reduction — the latter especially visible on Artificial Analysis tracking.
2. OpenAI shipped GPT-5.5 + Codex updates late April with cloud agents, parallel work, and persistent computer-use sessions. The agent layer is OpenAI’s clear differentiator now.
3. Independent reviewers spent April benchmarking with neutral harnesses, which is when the 6-4 capability split surfaced — versus the vendor-flavored ‘overall winner’ framing that dominated launch coverage.

Decision tree for May 2026

• You write a lot of code → Claude Opus 4.7 (Claude Code or Cursor 3 with Anthropic backend).
• You delegate long autonomous tasks → GPT-5.5 + Codex Cloud.
• You work with video, large multimodal docs, or research synthesis → Gemini 3.1 Pro.
• You want one for everything → Claude Opus 4.7 is the safest default in May 2026, with the trade-off that you’ll occasionally wish for stronger agentic chains; in those cases hop to GPT-5.5.
• You’re budget-constrained → Gemini 3.1 Pro for context-heavy work, GPT-5.5 mini for everyday chat.

Does Claude Mythos change this?

Not yet. Claude Mythos Preview, gated through Project Glasswing, is reportedly stronger than Opus 4.7 on cybersecurity, autonomous coding, and long-running agents. As of May 1, 2026 it is not on the API and not in Claude.ai for general users. Watch the Q3 2026 timeframe — if Anthropic widens access, the picture shifts again. For now, don’t make a buying decision based on Mythos.

Bottom line

The May 2026 frontier-model picture is a split, not a sweep. Claude Opus 4.7 leads on capability and careful work, GPT-5.5 leads on agents and computer use, Gemini 3.1 Pro leads on multimodal and price. Match the model to the workload — and budget for two subscriptions if your work straddles two of these axes, because the gap between “best fit” and “second best” is meaningful for productive work.

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