Claude Mythos 5.1 vs GPT-5.3 Codex

Pricing verdict: Claude Mythos 5.1 vs GPT-5.3 Codex: GPT-5.3 Codex is cheaper for input-heavy usage ($1.75/M vs $10.00/M input tokens), while Claude Mythos 5.1 is better for long-context tasks (1,000,000 tokens).

Direct answer: choose GPT-5.3 Codex for lower token spend and choose Claude Mythos 5.1 when your workload needs longer context.

Compare API pricing, input and output token costs, context windows, and monthly estimates on one page so you can pick the right model fast.

Anthropic

Claude Mythos 5.1

OpenAI

GPT-5.3 Codex

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Claude Mythos 5.1 pricing page GPT-5.3 Codex pricing page Anthropic provider overview OpenAI provider overview

Cost Comparison (1000 input + 500 output tokens, 100 requests/day)

Claude Mythos 5.1

Per Request:$0.035

Daily:$3.50

Monthly:$105.00

Yearly:$1,277.50

GPT-5.3 Codex

Per Request:$0.008750

Daily:$0.875

Monthly:$26.25

Yearly:$319.375

Cost Differences

$0.02625

Per Request

$2.625

Daily

$78.75

Monthly

$958.125

Yearly

GPT-5.3 Codex costs less than Claude Mythos 5.1

Quick Recommendation

Winner for direct API pricing: GPT-5.3 Codex. At the default workload, GPT-5.3 Codex saves about $78.75/month ($958.125/year) versus Claude Mythos 5.1.

Claude Mythos 5.1 full pricing breakdown GPT-5.3 Codex full pricing breakdown Anthropic API pricing details OpenAI API pricing details Anthropic vs OpenAI API pricing GPT-6 Astra vs Codex Mini GPT-6 Astra vs o4-mini Deep Research

Feature Comparison

Feature	Claude Mythos 5.1	GPT-5.3 Codex
Provider	Anthropic	OpenAI
Input Price	$10.00/1M tokens	$1.75/1M tokens
Output Price	$50.00/1M tokens	$14.00/1M tokens
Context Window	1,000,000 tokens	256,000 tokens
Max Output	128,000 tokens	32,768 tokens
Category	flagship	coding
Capabilities	textvisionreasoningcode	textcode
Release Date	9/1/2026	3/1/2026

Claude Mythos 5.1 vs GPT-5.3 Codex: Which Should You Choose?

Choosing between Claude Mythos 5.1 and GPT-5.3 Codex depends on your priorities: cost efficiency, context length, or raw capability. GPT-5.3 Codex is the more affordable option at $1.75/1M input tokens — 83% cheaper than Claude Mythos 5.1. Meanwhile, Claude Mythos 5.1 offers a significantly larger context window at 1,000,000 tokens vs 256,000 for GPT-5.3 Codex.

These models come from different providers — Anthropic and OpenAI — which means different API ecosystems, SDKs, rate limits, and terms of service. If you're already integrated with Anthropic, switching to OpenAIinvolves migration effort beyond just pricing. Factor in your existing infrastructure when deciding.

These models target different tiers: Claude Mythos 5.1 is a flagship model while GPT-5.3 Codex is coding. This means they're optimized for different workloads. Claude Mythos 5.1 is built for complex tasks that require deeper reasoning, while GPT-5.3 Codex offers better value for routine operations.

Output costs matter too. Claude Mythos 5.1 charges $50.00/1M output tokens vs $14.00 for GPT-5.3 Codex. For generation-heavy workloads (content creation, code generation, summarization), output pricing often dominates your bill. GPT-5.3 Codex has the edge here at $14.00/1M output tokens.

Multimodal capabilities: Claude Mythos 5.1 supports vision (image inputs) while GPT-5.3 Codex is text-only. If your application needs image understanding, this narrows your choice.

Best Use Cases

Choose Claude Mythos 5.1 when:

• You need a larger context window (1,000,000 tokens)
• You need more capabilities (vision, reasoning)
• You need longer outputs (up to 128,000 tokens)
• You're already using Anthropic's API ecosystem

Choose GPT-5.3 Codex when:

• Budget is a primary concern
• You're already using OpenAI's API ecosystem

Pros and Caveats at a Glance

Claude Mythos 5.1

• Input pricing: $10.00/M tokens
• Output pricing: $50.00/M tokens
• Context window: 1,000,000 tokens
• Max output: 128,000 tokens

Watch out for

• Higher input cost than GPT-5.3 Codex
• Higher output cost than GPT-5.3 Codex

GPT-5.3 Codex

• Input pricing: $1.75/M tokens
• Output pricing: $14.00/M tokens
• Context window: 256,000 tokens
• Max output: 32,768 tokens

Watch out for

• Smaller context window than Claude Mythos 5.1

Try Different Scenarios

Use the calculator below to see how costs change with different usage patterns

Claude Mythos 5.1 (Anthropic)

Cost Calculator

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GPT-5.3 Codex (OpenAI)

Cost Calculator

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Frequently Asked Questions

Which is cheaper, Claude Mythos 5.1 or GPT-5.3 Codex?▼

GPT-5.3 Codex is cheaper for input tokens at $1.75 per million tokens vs $10.00 for Claude Mythos 5.1 — that's 83% savings on input costs.

What is the context window difference between Claude Mythos 5.1 and GPT-5.3 Codex?▼

Claude Mythos 5.1 supports 1,000,000 tokens while GPT-5.3 Codex supports 256,000 tokens — a difference of 744,000 tokens in favor of Claude Mythos 5.1.

Which model is better for AI Chatbot?▼

Both models support text. For ai chatbot, GPT-5.3 Codex is the lower-cost option, while Claude Mythos 5.1 offers a larger context window (1,000,000 vs 256,000 tokens). Choose GPT-5.3 Codex for budget sensitivity or Claude Mythos 5.1 for longer context tasks.

Which model has better overall pricing for heavy usage?▼

At 100 requests/day with 1,000 input and 500 output tokens each, Claude Mythos 5.1 costs about $105.00/month and GPT-5.3 Codex costs about $26.25/month. Overall, GPT-5.3 Codex has lower combined input + output rates ($1.75 in, $14.00 out) vs Claude Mythos 5.1.

Where can I compare Anthropic and OpenAI API pricing beyond this model matchup?▼

See the Anthropic vs OpenAI provider comparison page for lineup-level averages, then review each model page for exact per-token rates.