Pick Claude Sonnet 4.5 for agentic coding — 77.2% on swe-bench verified, the best score any model had posted at its launch or computer use and gui automation (61.4% osworld at launch). Pick GPT-5.5 for terminal, cli and computer-use automation or long-horizon tool sequencing. On a tight budget at scale, Claude Sonnet 4.5 is the value pick.
Claude Sonnet 4.5 (Anthropic) and GPT-5.5 (OpenAI) are two of the models people most often weigh against each other in 2026. Claude Sonnet 4.5 is september 2025's coding state of the art at $3/$15 — still supported, but 200K-capped and twice superseded. GPT-5.5 is openAI's first fully retrained base since GPT-4.5 — the terminal and computer-use champion. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences
Price: Claude Sonnet 4.5 is about 1.7× cheaper on input ($3/$15 per 1M tokens vs $5/$30 per 1M tokens) — modest, but it adds up at steady volume.
Context window: GPT-5.5 holds 5× more — 1M (~1,500 pages) vs 200K (~300 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
Recency: GPT-5.5 is the newer model by about 7 months (released April 23, 2026), usually meaning fresher training data and capabilities.
Specifications
Spec
Claude Sonnet 4.5
GPT-5.5
Provider
Anthropic (US)
OpenAI (US)
Released
September 29, 2025
April 23, 2026
Context window
200K (~300 pages)
1M (~1,500 pages)
Price (in/out)
$3/$15 per 1M tokens
$5/$30 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, code
text, image, code
SWE-Bench Verified
77.2%
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Agentic coding — 77.2% on SWE-Bench Verified, the best score any model had posted at its launch: Claude Sonnet 4.5 — GPT-5.5 is comparatively weak here — trails Opus 4.8 on hardest coding benchmarks
Computer use and GUI automation (61.4% OSWorld at launch): Claude Sonnet 4.5 — September 2025's coding state of the art at $3/$15 — still supported, but 200K-capped and twice superseded — and it runs cheaper at $3/$15 per 1M tokens.
Long-horizon autonomy — Anthropic reported 30+ hours of sustained focus on multi-step tasks: Claude Sonnet 4.5 — Claude Sonnet 4.5 lists long-horizon autonomy — Anthropic reported 30+ hours of sustained focus on multi-step tasks among its strengths; GPT-5.5 does not.
Terminal, CLI and computer-use automation: GPT-5.5 — OpenAI's first fully retrained base since GPT-4.5 — the terminal and computer-use champion — and it carries the larger 1M context.
Long-horizon tool sequencing: GPT-5.5 — Its 1M window holds about 5× more than Claude Sonnet 4.5's 200K in a single prompt.
Strong agentic coding and reasoning: GPT-5.5 — OpenAI's first fully retrained base since GPT-4.5 — the terminal and computer-use champion — and it is the newer of the two.
Lowest cost at scale: Claude Sonnet 4.5 — At $3/$15 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input: GPT-5.5 — Its 1M window is about 5× larger than Claude Sonnet 4.5's 200K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume: Claude Sonnet 4.5 — At $3/$15 per 1M tokens it undercuts GPT-5.5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases: GPT-5.5 — Larger 1M window fits more in one prompt.
Anyone whose priority is agentic coding — 77.2% on swe-bench verified, the best score any model had posted at its launch: Claude Sonnet 4.5 — It is specifically built for that.
Anyone whose priority is terminal, cli and computer-use automation: GPT-5.5 — That is its strongest area.
Claude Sonnet 4.5: where it fits
September 2025's coding state of the art at $3/$15 — still supported, but 200K-capped and twice superseded. Released September 29, 2025 by Anthropic, it is built for agentic coding — 77.2% on SWE-Bench Verified, the best score any model had posted at its launch, computer use and GUI automation (61.4% OSWorld at launch), long-horizon autonomy — Anthropic reported 30+ hours of sustained focus on multi-step tasks, and tracking its own remaining token budget natively, which few models do.
Its trade-offs are real: superseded twice — Sonnet 4.6 and Sonnet 5 match or beat it at the same or lower price, capped at 200K since Anthropic retired its 1M beta in April 2026, while its successors ship 1M as standard, and missing the modern API surface: no adaptive thinking, no effort control, and half the max output of newer Sonnets. At $3 in / $15 out per million tokens, it sits in the mid price band.
GPT-5.5: where it fits
OpenAI's first fully retrained base since GPT-4.5 — the terminal and computer-use champion. Released April 23, 2026 by OpenAI, it is built for terminal, CLI and computer-use automation, long-horizon tool sequencing, strong agentic coding and reasoning, and browser-driving agents.
Its trade-offs: trails Opus 4.8 on hardest coding benchmarks, and tiered long-context pricing above 272K tokens. At $5 in / $30 out per million tokens, it sits in the premium price band.
The bottom line for this matchup
Claude Sonnet 4.5 and GPT-5.5 overlap enough that the right pick depends on your specific job. Claude Sonnet 4.5 costs less per token; GPT-5.5 holds the larger context; and each leads in its own area — Claude Sonnet 4.5 for agentic coding — 77.2% on swe-bench verified, the best score any model had posted at its launch, GPT-5.5 for terminal, cli and computer-use automation. Rather than crowning one, run the same hard task through both once and let the results decide.
Frequently asked questions
Is Claude Sonnet 4.5 or GPT-5.5 better for coding?
Public SWE-Bench figures are not available for GPT-5.5, so the honest test is your own repository — run an identical real bug through both. By design, Claude Sonnet 4.5 leans toward agentic coding — 77.2% on swe-bench verified, the best score any model had posted at its launch while GPT-5.5 leans toward terminal, cli and computer-use automation, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Sonnet 4.5 or GPT-5.5?
Claude Sonnet 4.5 is cheaper — $3/$15 per 1M tokens vs $5/$30 per 1M tokens, roughly 1.7× apart on input.
Which has the bigger context window?
GPT-5.5 — 1M vs 200K, about 5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both Claude Sonnet 4.5 and GPT-5.5 together?
Yes — a multi-model platform like LumiChats gives you Claude Sonnet 4.5, GPT-5.5 and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, Claude Sonnet 4.5 or GPT-5.5?
GPT-5.5 — released April 23, 2026, about 7 months after Claude Sonnet 4.5.
Claude Sonnet 4.5 vs GPT-5.5
Anthropic · US | OpenAI · US · Updated June 2026
Quick verdict
Pick Claude Sonnet 4.5 for agentic coding — 77.2% on swe-bench verified, the best score any model had posted at its launch or computer use and gui automation (61.4% osworld at launch). Pick GPT-5.5 for terminal, cli and computer-use automation or long-horizon tool sequencing. On a tight budget at scale, Claude Sonnet 4.5 is the value pick.
Claude Sonnet 4.5 (Anthropic) and GPT-5.5 (OpenAI) are two of the models people most often weigh against each other in 2026. Claude Sonnet 4.5 is september 2025's coding state of the art at $3/$15 — still supported, but 200K-capped and twice superseded. GPT-5.5 is openAI's first fully retrained base since GPT-4.5 — the terminal and computer-use champion. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences at a glance
▸Price: Claude Sonnet 4.5 is about 1.7× cheaper on input ($3/$15 per 1M tokens vs $5/$30 per 1M tokens) — modest, but it adds up at steady volume.
▸Context window: GPT-5.5 holds 5× more — 1M (~1,500 pages) vs 200K (~300 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
▸Recency: GPT-5.5 is the newer model by about 7 months (released April 23, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
Spec
Claude Sonnet 4.5
GPT-5.5
Provider
Anthropic (US)
OpenAI (US)
Released
September 29, 2025
April 23, 2026
Context window
200K (~300 pages)
1M (~1,500 pages)
Price (in/out)
$3/$15 per 1M tokens
$5/$30 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, code
text, image, code
SWE-Bench Verified
77.2%
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Agentic coding — 77.2% on SWE-Bench Verified, the best score any model had posted at its launch
Claude Sonnet 4.5
GPT-5.5 is comparatively weak here — trails Opus 4.8 on hardest coding benchmarks
Computer use and GUI automation (61.4% OSWorld at launch)
Claude Sonnet 4.5
September 2025's coding state of the art at $3/$15 — still supported, but 200K-capped and twice superseded — and it runs cheaper at $3/$15 per 1M tokens.
Long-horizon autonomy — Anthropic reported 30+ hours of sustained focus on multi-step tasks
Claude Sonnet 4.5
Claude Sonnet 4.5 lists long-horizon autonomy — Anthropic reported 30+ hours of sustained focus on multi-step tasks among its strengths; GPT-5.5 does not.
Terminal, CLI and computer-use automation
GPT-5.5
OpenAI's first fully retrained base since GPT-4.5 — the terminal and computer-use champion — and it carries the larger 1M context.
Long-horizon tool sequencing
GPT-5.5
Its 1M window holds about 5× more than Claude Sonnet 4.5's 200K in a single prompt.
Strong agentic coding and reasoning
GPT-5.5
OpenAI's first fully retrained base since GPT-4.5 — the terminal and computer-use champion — and it is the newer of the two.
Lowest cost at scale
Claude Sonnet 4.5
At $3/$15 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input
GPT-5.5
Its 1M window is about 5× larger than Claude Sonnet 4.5's 200K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume
→ Claude Sonnet 4.5
At $3/$15 per 1M tokens it undercuts GPT-5.5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases
→ GPT-5.5
Larger 1M window fits more in one prompt.
Anyone whose priority is agentic coding — 77.2% on swe-bench verified, the best score any model had posted at its launch
→ Claude Sonnet 4.5
It is specifically built for that.
Anyone whose priority is terminal, cli and computer-use automation
→ GPT-5.5
That is its strongest area.
Claude Sonnet 4.5: where it fits
September 2025's coding state of the art at $3/$15 — still supported, but 200K-capped and twice superseded. Released September 29, 2025 by Anthropic, it is built for agentic coding — 77.2% on SWE-Bench Verified, the best score any model had posted at its launch, computer use and GUI automation (61.4% OSWorld at launch), long-horizon autonomy — Anthropic reported 30+ hours of sustained focus on multi-step tasks, and tracking its own remaining token budget natively, which few models do.
Its trade-offs are real: superseded twice — Sonnet 4.6 and Sonnet 5 match or beat it at the same or lower price, capped at 200K since Anthropic retired its 1M beta in April 2026, while its successors ship 1M as standard, and missing the modern API surface: no adaptive thinking, no effort control, and half the max output of newer Sonnets. At $3 in / $15 out per million tokens, it sits in the mid price band.
GPT-5.5: where it fits
OpenAI's first fully retrained base since GPT-4.5 — the terminal and computer-use champion. Released April 23, 2026 by OpenAI, it is built for terminal, CLI and computer-use automation, long-horizon tool sequencing, strong agentic coding and reasoning, and browser-driving agents.
Its trade-offs: trails Opus 4.8 on hardest coding benchmarks, and tiered long-context pricing above 272K tokens. At $5 in / $30 out per million tokens, it sits in the premium price band.
The bottom line for this matchup
Claude Sonnet 4.5 and GPT-5.5 overlap enough that the right pick depends on your specific job. Claude Sonnet 4.5 costs less per token; GPT-5.5 holds the larger context; and each leads in its own area — Claude Sonnet 4.5 for agentic coding — 77.2% on swe-bench verified, the best score any model had posted at its launch, GPT-5.5 for terminal, cli and computer-use automation. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both Claude Sonnet 4.5 and GPT-5.5 without two subscriptions? LumiChats gives you these plus 40+ models under one ₹69/day pass (about $1/day) — draft with one, cross-check with the other.
Is Claude Sonnet 4.5 or GPT-5.5 better for coding?
Public SWE-Bench figures are not available for GPT-5.5, so the honest test is your own repository — run an identical real bug through both. By design, Claude Sonnet 4.5 leans toward agentic coding — 77.2% on swe-bench verified, the best score any model had posted at its launch while GPT-5.5 leans toward terminal, cli and computer-use automation, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Sonnet 4.5 or GPT-5.5?
Claude Sonnet 4.5 is cheaper — $3/$15 per 1M tokens vs $5/$30 per 1M tokens, roughly 1.7× apart on input.
Which has the bigger context window?
GPT-5.5 — 1M vs 200K, about 5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both Claude Sonnet 4.5 and GPT-5.5 together?
Yes — a multi-model platform like LumiChats gives you Claude Sonnet 4.5, GPT-5.5 and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, Claude Sonnet 4.5 or GPT-5.5?
GPT-5.5 — released April 23, 2026, about 7 months after Claude Sonnet 4.5.
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.