Pick Claude Sonnet 5 for agentic workflows that plan, use tools, and run autonomously or multi-step coding, debugging, and tool use. 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 Sonnet 5 (Anthropic) and GPT-5.3-Codex (OpenAI) are two of the models people most often weigh against each other in 2026. Claude Sonnet 5 is anthropic's most agentic Sonnet, with near-Opus-4.8 performance at Sonnet prices; the default model on Free and Pro. 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 1.7× cheaper on input ($1.75/$14 per 1M tokens vs $3/$15 per 1M tokens) — modest, but it adds up at steady volume.
Context window: Claude Sonnet 5 holds 2.5× more — 1M (~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 Sonnet 5 is the newer model by about 4 months (released June 30, 2026), usually meaning fresher training data and capabilities.
Specifications
Spec
Claude Sonnet 5
GPT-5.3-Codex
Provider
Anthropic (US)
OpenAI (US)
Released
June 30, 2026
February 24, 2026
Context window
1M (~1,500 pages)
400K (~600 pages)
Price (in/out)
$3/$15 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
Agentic workflows that plan, use tools, and run autonomously: Claude Sonnet 5 — A core design strength of Claude Sonnet 5.
Multi-step coding, debugging, and tool use: Claude Sonnet 5 — A core design strength of Claude Sonnet 5.
Everyday professional and knowledge work: Claude Sonnet 5 — A core design strength of Claude Sonnet 5.
Dedicated coding agent: GPT-5.3-Codex — A core design strength of GPT-5.3-Codex.
CLI and IDE integration: GPT-5.3-Codex — A core design strength of GPT-5.3-Codex.
Autonomous software tasks: GPT-5.3-Codex — A core design strength of GPT-5.3-Codex.
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 Sonnet 5 — Its 1M window is about 2.5× larger, 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 Sonnet 5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases: Claude Sonnet 5 — Larger 1M window fits more in one prompt.
Anyone whose priority is agentic workflows that plan, use tools, and run autonomously: Claude Sonnet 5 — It is specifically built for that.
Anyone whose priority is dedicated coding agent: GPT-5.3-Codex — That is its strongest area.
Claude Sonnet 5: where it fits
Anthropic's most agentic Sonnet, with near-Opus-4.8 performance at Sonnet prices; the default model on Free and Pro. Released June 30, 2026 by Anthropic, it is built for agentic workflows that plan, use tools, and run autonomously, multi-step coding, debugging, and tool use, everyday professional and knowledge work, and long-document analysis and reasoning.
Its trade-offs are real: lower peak accuracy than Opus 4.8 on the hardest tasks, and an updated tokenizer that can use 1.0-1.35x more tokens for the same text. At $3 in / $15 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 24, 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 Sonnet 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 Sonnet 5 holds the larger context; and each leads in its own area — Claude Sonnet 5 for agentic workflows that plan, use tools, and run autonomously, 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 Sonnet 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 Sonnet 5 leans toward agentic workflows that plan, use tools, and run autonomously 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 Sonnet 5 or GPT-5.3-Codex?
GPT-5.3-Codex is cheaper — $3/$15 per 1M tokens vs $1.75/$14 per 1M tokens, roughly 1.7× apart on input.
Which has the bigger context window?
Claude Sonnet 5 — 1M 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 Sonnet 5 and GPT-5.3-Codex together?
Yes — a multi-model platform like LumiChats gives you Claude Sonnet 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 Sonnet 5 or GPT-5.3-Codex?
Claude Sonnet 5 — released June 30, 2026, about 4 months after GPT-5.3-Codex.
Claude Sonnet 5 vs GPT-5.3-Codex
Anthropic · US | OpenAI · US · Updated June 2026
Quick verdict
Pick Claude Sonnet 5 for agentic workflows that plan, use tools, and run autonomously or multi-step coding, debugging, and tool use. 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 Sonnet 5 (Anthropic) and GPT-5.3-Codex (OpenAI) are two of the models people most often weigh against each other in 2026. Claude Sonnet 5 is anthropic's most agentic Sonnet, with near-Opus-4.8 performance at Sonnet prices; the default model on Free and Pro. 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 1.7× cheaper on input ($1.75/$14 per 1M tokens vs $3/$15 per 1M tokens) — modest, but it adds up at steady volume.
▸Context window: Claude Sonnet 5 holds 2.5× more — 1M (~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 Sonnet 5 is the newer model by about 4 months (released June 30, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
Spec
Claude Sonnet 5
GPT-5.3-Codex
Provider
Anthropic (US)
OpenAI (US)
Released
June 30, 2026
February 24, 2026
Context window
1M (~1,500 pages)
400K (~600 pages)
Price (in/out)
$3/$15 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
Agentic workflows that plan, use tools, and run autonomously
Claude Sonnet 5
A core design strength of Claude Sonnet 5.
Multi-step coding, debugging, and tool use
Claude Sonnet 5
A core design strength of Claude Sonnet 5.
Everyday professional and knowledge work
Claude Sonnet 5
A core design strength of Claude Sonnet 5.
Dedicated coding agent
GPT-5.3-Codex
A core design strength of GPT-5.3-Codex.
CLI and IDE integration
GPT-5.3-Codex
A core design strength of GPT-5.3-Codex.
Autonomous software tasks
GPT-5.3-Codex
A core design strength of GPT-5.3-Codex.
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 Sonnet 5
Its 1M window is about 2.5× larger, 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 Sonnet 5, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases
→ Claude Sonnet 5
Larger 1M window fits more in one prompt.
Anyone whose priority is agentic workflows that plan, use tools, and run autonomously
→ Claude Sonnet 5
It is specifically built for that.
Anyone whose priority is dedicated coding agent
→ GPT-5.3-Codex
That is its strongest area.
Claude Sonnet 5: where it fits
Anthropic's most agentic Sonnet, with near-Opus-4.8 performance at Sonnet prices; the default model on Free and Pro. Released June 30, 2026 by Anthropic, it is built for agentic workflows that plan, use tools, and run autonomously, multi-step coding, debugging, and tool use, everyday professional and knowledge work, and long-document analysis and reasoning.
Its trade-offs are real: lower peak accuracy than Opus 4.8 on the hardest tasks, and an updated tokenizer that can use 1.0-1.35x more tokens for the same text. At $3 in / $15 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 24, 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 Sonnet 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 Sonnet 5 holds the larger context; and each leads in its own area — Claude Sonnet 5 for agentic workflows that plan, use tools, and run autonomously, 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 Sonnet 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 Sonnet 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 Sonnet 5 leans toward agentic workflows that plan, use tools, and run autonomously 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 Sonnet 5 or GPT-5.3-Codex?
GPT-5.3-Codex is cheaper — $3/$15 per 1M tokens vs $1.75/$14 per 1M tokens, roughly 1.7× apart on input.
Which has the bigger context window?
Claude Sonnet 5 — 1M 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 Sonnet 5 and GPT-5.3-Codex together?
Yes — a multi-model platform like LumiChats gives you Claude Sonnet 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 Sonnet 5 or GPT-5.3-Codex?
Claude Sonnet 5 — released June 30, 2026, about 4 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.