Pick Claude Opus 5.5 for performs at roughly claude fable 5.1's level on most work, at 40% lower typical workload cost than opus 5 or anthropic reports it surpasses fable 5.1 on agentic coding, knowledge work, computer use, visual chart recognition, and multidisciplinary reasoning. Pick GPT-5.3-Codex for dedicated coding agent or cli and ide integration. On a tight budget at scale, GPT-5.3-Codex is the value pick.
Claude Opus 5.5 (Anthropic) and GPT-5.3-Codex (OpenAI) are two of the models people most often weigh against each other in 2026. Claude Opus 5.5 is anthropic's September 22, 2026 update: Fable 5.1-level performance at 40% lower cost than Opus 5, with faster output and cheaper caching. GPT-5.3-Codex is openAI's coding-specialized agent model for autonomous software engineering. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences
Price: GPT-5.3-Codex is about 2.3× cheaper on input ($1.75/$14 per 1M tokens vs $4/$20 per 1M tokens) — meaningful once you are processing millions of tokens a month.
Context window: Claude Opus 5.5 holds 2.5× more — 1M tokens (~1,500 pages) vs 400K (~600 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
Recency: Claude Opus 5.5 is the newer model by about 8 months (released September 22, 2026), usually meaning fresher training data and capabilities.
Specifications
Spec
Claude Opus 5.5
GPT-5.3-Codex
Provider
Anthropic (US)
OpenAI (US)
Released
September 22, 2026
February 5, 2026
Context window
1M tokens (~1,500 pages)
400K (~600 pages)
Price (in/out)
$4/$20 per 1M tokens
$1.75/$14 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, code
text, code
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Performs at roughly Claude Fable 5.1's level on most work, at 40% lower typical workload cost than Opus 5: Claude Opus 5.5 — Anthropic's September 22, 2026 update: Fable 5.1-level performance at 40% lower cost than Opus 5, with faster output and cheaper caching — and it carries the larger 1M tokens context.
Anthropic reports it surpasses Fable 5.1 on agentic coding, knowledge work, computer use, visual chart recognition, and multidisciplinary reasoning: Claude Opus 5.5 — GPT-5.3-Codex is comparatively weak here — coding-specialized, narrower general use
Pricing cut to $4/$20 per million tokens (20% below Opus 5's $5/$25), cache reads down 60% to $0.20/MTok: Claude Opus 5.5 — Its 1M tokens window holds about 2.5× more than GPT-5.3-Codex's 400K in a single prompt.
Dedicated coding agent: GPT-5.3-Codex — OpenAI's coding-specialized agent model for autonomous software engineering — and it runs cheaper at $1.75/$14 per 1M tokens.
CLI and IDE integration: GPT-5.3-Codex — GPT-5.3-Codex lists cLI and IDE integration among its strengths; Claude Opus 5.5 does not.
Autonomous software tasks: GPT-5.3-Codex — GPT-5.3-Codex lists autonomous software tasks among its strengths; Claude Opus 5.5 does not.
Lowest cost at scale: GPT-5.3-Codex — At $1.75/$14 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input: Claude Opus 5.5 — Its 1M tokens window is about 2.5× larger than GPT-5.3-Codex's 400K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume: GPT-5.3-Codex — At $1.75/$14 per 1M tokens it undercuts Claude Opus 5.5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases: Claude Opus 5.5 — Larger 1M tokens window fits more in one prompt.
Anyone whose priority is performs at roughly claude fable 5.1's level on most work, at 40% lower typical workload cost than opus 5: Claude Opus 5.5 — It is specifically built for that.
Anyone whose priority is dedicated coding agent: GPT-5.3-Codex — That is its strongest area.
Claude Opus 5.5: where it fits
Anthropic's September 22, 2026 update: Fable 5.1-level performance at 40% lower cost than Opus 5, with faster output and cheaper caching. Released September 22, 2026 by Anthropic, it is built for performs at roughly Claude Fable 5.1's level on most work, at 40% lower typical workload cost than Opus 5, anthropic reports it surpasses Fable 5.1 on agentic coding, knowledge work, computer use, visual chart recognition, and multidisciplinary reasoning, pricing cut to $4/$20 per million tokens (20% below Opus 5's $5/$25), cache reads down 60% to $0.20/MTok, and output speed increased over 30% versus Opus 5.
Its trade-offs are real: not a reasoning-ceiling upgrade over Fable 5.1 — pitched as matching its performance at lower cost, not beating it outright, like Opus 5, the headline 1M-token context is not uniformly available across every platform and plan — some API paths default to a smaller window, and first model in the 5.5 line; Anthropic has signaled Sonnet 5.5 and Haiku 5.5 are still weeks away, so the lower tiers of the family aren't out yet. At $4 in / $20 out per million tokens, it sits in the mid price band.
GPT-5.3-Codex: where it fits
OpenAI's coding-specialized agent model for autonomous software engineering. Released February 5, 2026 by OpenAI, it is built for dedicated coding agent, cLI and IDE integration, autonomous software tasks, and tool calling.
Its trade-offs: coding-specialized, narrower general use, and retired in favor of GPT-5.5 Codex. At $1.75 in / $14 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Claude Opus 5.5 and GPT-5.3-Codex overlap enough that the right pick depends on your specific job. GPT-5.3-Codex costs less per token; Claude Opus 5.5 holds the larger context; and each leads in its own area — Claude Opus 5.5 for performs at roughly claude fable 5.1's level on most work, at 40% lower typical workload cost than opus 5, GPT-5.3-Codex for dedicated coding agent. Rather than crowning one, run the same hard task through both once and let the results decide.
Frequently asked questions
Is Claude Opus 5.5 or GPT-5.3-Codex better for coding?
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, Claude Opus 5.5 leans toward performs at roughly claude fable 5.1's level on most work, at 40% lower typical workload cost than opus 5 while GPT-5.3-Codex leans toward dedicated coding agent, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Opus 5.5 or GPT-5.3-Codex?
GPT-5.3-Codex is cheaper — $4/$20 per 1M tokens vs $1.75/$14 per 1M tokens, roughly 2.3× apart on input.
Which has the bigger context window?
Claude Opus 5.5 — 1M tokens vs 400K, about 2.5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both Claude Opus 5.5 and GPT-5.3-Codex together?
Yes — a multi-model platform like LumiChats gives you Claude Opus 5.5, GPT-5.3-Codex 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 Opus 5.5 or GPT-5.3-Codex?
Claude Opus 5.5 — released September 22, 2026, about 8 months after GPT-5.3-Codex.
Claude Opus 5.5 vs GPT-5.3-Codex
Anthropic · US | OpenAI · US · Updated June 2026
Quick verdict
Pick Claude Opus 5.5 for performs at roughly claude fable 5.1's level on most work, at 40% lower typical workload cost than opus 5 or anthropic reports it surpasses fable 5.1 on agentic coding, knowledge work, computer use, visual chart recognition, and multidisciplinary reasoning. Pick GPT-5.3-Codex for dedicated coding agent or cli and ide integration. On a tight budget at scale, GPT-5.3-Codex is the value pick.
Claude Opus 5.5 (Anthropic) and GPT-5.3-Codex (OpenAI) are two of the models people most often weigh against each other in 2026. Claude Opus 5.5 is anthropic's September 22, 2026 update: Fable 5.1-level performance at 40% lower cost than Opus 5, with faster output and cheaper caching. GPT-5.3-Codex is openAI's coding-specialized agent model for autonomous software engineering. They diverge most on price and context window — each quantified below from the models' real specs.
Key differences at a glance
▸Price: GPT-5.3-Codex is about 2.3× cheaper on input ($1.75/$14 per 1M tokens vs $4/$20 per 1M tokens) — meaningful once you are processing millions of tokens a month.
▸Context window: Claude Opus 5.5 holds 2.5× more — 1M tokens (~1,500 pages) vs 400K (~600 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
▸Recency: Claude Opus 5.5 is the newer model by about 8 months (released September 22, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
Spec
Claude Opus 5.5
GPT-5.3-Codex
Provider
Anthropic (US)
OpenAI (US)
Released
September 22, 2026
February 5, 2026
Context window
1M tokens (~1,500 pages)
400K (~600 pages)
Price (in/out)
$4/$20 per 1M tokens
$1.75/$14 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, code
text, code
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Performs at roughly Claude Fable 5.1's level on most work, at 40% lower typical workload cost than Opus 5
Claude Opus 5.5
Anthropic's September 22, 2026 update: Fable 5.1-level performance at 40% lower cost than Opus 5, with faster output and cheaper caching — and it carries the larger 1M tokens context.
Anthropic reports it surpasses Fable 5.1 on agentic coding, knowledge work, computer use, visual chart recognition, and multidisciplinary reasoning
Claude Opus 5.5
GPT-5.3-Codex is comparatively weak here — coding-specialized, narrower general use
Pricing cut to $4/$20 per million tokens (20% below Opus 5's $5/$25), cache reads down 60% to $0.20/MTok
Claude Opus 5.5
Its 1M tokens window holds about 2.5× more than GPT-5.3-Codex's 400K in a single prompt.
Dedicated coding agent
GPT-5.3-Codex
OpenAI's coding-specialized agent model for autonomous software engineering — and it runs cheaper at $1.75/$14 per 1M tokens.
CLI and IDE integration
GPT-5.3-Codex
GPT-5.3-Codex lists cLI and IDE integration among its strengths; Claude Opus 5.5 does not.
Autonomous software tasks
GPT-5.3-Codex
GPT-5.3-Codex lists autonomous software tasks among its strengths; Claude Opus 5.5 does not.
Lowest cost at scale
GPT-5.3-Codex
At $1.75/$14 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input
Claude Opus 5.5
Its 1M tokens window is about 2.5× larger than GPT-5.3-Codex's 400K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume
→ GPT-5.3-Codex
At $1.75/$14 per 1M tokens it undercuts Claude Opus 5.5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases
→ Claude Opus 5.5
Larger 1M tokens window fits more in one prompt.
Anyone whose priority is performs at roughly claude fable 5.1's level on most work, at 40% lower typical workload cost than opus 5
→ Claude Opus 5.5
It is specifically built for that.
Anyone whose priority is dedicated coding agent
→ GPT-5.3-Codex
That is its strongest area.
Claude Opus 5.5: where it fits
Anthropic's September 22, 2026 update: Fable 5.1-level performance at 40% lower cost than Opus 5, with faster output and cheaper caching. Released September 22, 2026 by Anthropic, it is built for performs at roughly Claude Fable 5.1's level on most work, at 40% lower typical workload cost than Opus 5, anthropic reports it surpasses Fable 5.1 on agentic coding, knowledge work, computer use, visual chart recognition, and multidisciplinary reasoning, pricing cut to $4/$20 per million tokens (20% below Opus 5's $5/$25), cache reads down 60% to $0.20/MTok, and output speed increased over 30% versus Opus 5.
Its trade-offs are real: not a reasoning-ceiling upgrade over Fable 5.1 — pitched as matching its performance at lower cost, not beating it outright, like Opus 5, the headline 1M-token context is not uniformly available across every platform and plan — some API paths default to a smaller window, and first model in the 5.5 line; Anthropic has signaled Sonnet 5.5 and Haiku 5.5 are still weeks away, so the lower tiers of the family aren't out yet. At $4 in / $20 out per million tokens, it sits in the mid price band.
GPT-5.3-Codex: where it fits
OpenAI's coding-specialized agent model for autonomous software engineering. Released February 5, 2026 by OpenAI, it is built for dedicated coding agent, cLI and IDE integration, autonomous software tasks, and tool calling.
Its trade-offs: coding-specialized, narrower general use, and retired in favor of GPT-5.5 Codex. At $1.75 in / $14 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Claude Opus 5.5 and GPT-5.3-Codex overlap enough that the right pick depends on your specific job. GPT-5.3-Codex costs less per token; Claude Opus 5.5 holds the larger context; and each leads in its own area — Claude Opus 5.5 for performs at roughly claude fable 5.1's level on most work, at 40% lower typical workload cost than opus 5, GPT-5.3-Codex for dedicated coding agent. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both Claude Opus 5.5 and GPT-5.3-Codex 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 Opus 5.5 or GPT-5.3-Codex better for coding?
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, Claude Opus 5.5 leans toward performs at roughly claude fable 5.1's level on most work, at 40% lower typical workload cost than opus 5 while GPT-5.3-Codex leans toward dedicated coding agent, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Opus 5.5 or GPT-5.3-Codex?
GPT-5.3-Codex is cheaper — $4/$20 per 1M tokens vs $1.75/$14 per 1M tokens, roughly 2.3× apart on input.
Which has the bigger context window?
Claude Opus 5.5 — 1M tokens vs 400K, about 2.5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both Claude Opus 5.5 and GPT-5.3-Codex together?
Yes — a multi-model platform like LumiChats gives you Claude Opus 5.5, GPT-5.3-Codex 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 Opus 5.5 or GPT-5.3-Codex?
Claude Opus 5.5 — released September 22, 2026, about 8 months after GPT-5.3-Codex.
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.